[Tiger Luck]

For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the far lower
right of the schematic, just above the separate, isolated schematic of the 15 volt
regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the cap was
correct. The corresponding cap in the other channel does not blow. Both caps have
the negative connected to the same source from the power supply and both have their
positives connected to ground. In other words, the negs of both caps are connected
together to the negative rail from the power supply and both positives are grounded,
yet one cap blows and the other doesn't. The cap blew with a sharp crack and the
rubber plug at the bottom blew out. The cap that blew is not shorted. It still acts
like a cap should when measured with an analog ohm meter. I installed another, new
cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two

[Chris Hornbeck]

On Wed, 10 Sep 2008 18:29:26 -0700, Tiger Luck
wrote:

The cap that blows is C313.

Any insights?

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

All the best fortune,
Chris Hornbeck

[Tiger Luck]

Chris Hornbeck wrote:
On Wed, 10 Sep 2008 18:29:26 -0700, Tiger Luck
wrote:

The cap that blows is C313.

Any insights?

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

All the best fortune,
Chris Hornbeck

Not a chance... cap installed correctly and worked for years.

Found at least one shorted tranny, maybe two.

Looking for equivalent to 2n5087 amongst my junk. NTE site says NTE159, but I have
only NTE99 and NTE 290A. Not sure if they swap so I have to put my joy to bed until
parts house opens manana.

--
Einstein forgot to carry the two

[Chris Hornbeck]

On Wed, 10 Sep 2008 21:23:45 -0700, Tiger Luck
wrote:

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

Not a chance... cap installed correctly and worked for years.

Are you saying that *ONE* capacitor has failed? Not
a series of replacements? The thing's 30 years old - *all*
of the electrolytic cap's are bad now. That's life.

Replace *all* of the electrolytics and move on. They're
*all* bad. Parts are cheap.


BTW, if your question had been about repeated failures,
the diagnosis would be: the cap got too hot. It got too
hot because it was defective, or it was exposed to too
high a voltage, or it was exposed to reverse voltage,
or it was cooked by ESR.

So, for future troubleshooting, eliminate these four
and you'll have only a mystery remaining!


Good fortune,
Chris Hornbeck

[Tiger Luck]

Chris Hornbeck wrote:
On Wed, 10 Sep 2008 21:23:45 -0700, Tiger Luck
wrote:

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

Not a chance... cap installed correctly and worked for years.

Are you saying that *ONE* capacitor has failed? Not
a series of replacements? The thing's 30 years old - *all*
of the electrolytic cap's are bad now. That's life.

Replace *all* of the electrolytics and move on. They're
*all* bad. Parts are cheap.

I replaced all the electro caps less than two years ago. Amp worked fine up until
now. Polarity was and is correct. After cap blew today, new replacement cap over
heated. I shut off power before it blew out.



BTW, if your question had been about repeated failures,
the diagnosis would be: the cap got too hot. It got too
hot because it was defective, or it was exposed to too
high a voltage,

I checked voltage across cap terminals with cap out. It read correctly.

or it was exposed to reverse voltage,

Trust me. Polarity was correct.

or it was cooked by ESR.

Equivalent series resistance? Is that a measure of quality?

Caps are no-names, both from the same parts house. hmm...


So, for future troubleshooting, eliminate these four
and you'll have only a mystery remaining!



Good fortune,
Chris Hornbeck


--
Einstein forgot to carry the two

[Chris Hornbeck]

On Wed, 10 Sep 2008 22:32:23 -0700, Tiger Luck
wrote:

I replaced all the electro caps less than two years ago. Amp worked fine up until
now. Polarity was and is correct. After cap blew today, new replacement cap over
heated. I shut off power before it blew out.

Cool. Leaves two main possibilities: the cap's simply defective,
or something's changed in its external world.

Defective is easy to test - fresh different batch cap.

The external world could include voltage (do you dare to
measure terminal voltages? - stick a big plastic cap in
temporarily for safety) and current (difficult to measure
directly, but can be inferred with a scope. More below.


I checked voltage across cap terminals with cap out. It read correctly.

Very cool. Also implies that the amp channel is not
oscillating. Maybe.


Trust me. Polarity was correct.

Oh, I trust you. It's me that I don't trust. (Never personally
been wrong, but there's always a first time. Actually, that
was personally some time before Kindergarten and I'm over it now).
But mistakes are part of Humanity - embrace errors. Arf!


or it was cooked by ESR.

Equivalent series resistance? Is that a measure of quality?
Caps are no-names, both from the same parts house. hmm...

All caps are slightly imperfect and must dissipate some actual
power with applied voltage. They leak some DC, but they also
"leak" some AC, so must dissipate some of the charging and
discharging currents.

An earlier poster has already suggested that the failure
of a "main" biggie electrolytic might have added stress to
this bypass cap, and charging/discharging currents would be
the medium. Your tests seem to have eliminated this as a
prime candidate, but... Can you measure ripple on the
supply lines? Might be interesting. A scope here is worth
a thousand words, fersure.

Any scope indication of any high frequency signal on the
supply line(s) is also worth effort. The bypass capacitor's
gig in life is to keep the amplifier happy at high frequencies.
But conversely, an unhappy amplifier can generate high
frequency currents that can damage a nearby capacitor (through
ESR (resistive)) losses. Like the bypass cap - could happen...


ps: I'm a big fan of the little Advent 300. Breathtaking
engineering. When I find the little snot that stole mine
(much modified and easily identifiable) I'm gonna make him
wish his momma had raised him better.

All the best fortune,
Chris Hornbeck

[[email protected]]

Tiger Luck wrote:
Chris Hornbeck wrote:
On Wed, 10 Sep 2008 21:23:45 -0700, Tiger Luck
wrote:

The best odds-on bet is that despite everything posted
the cap is reversed. Sorry, but that's the main line.

Not a chance... cap installed correctly and worked for years.

Are you saying that *ONE* capacitor has failed? Not
a series of replacements? The thing's 30 years old - *all*
of the electrolytic cap's are bad now. That's life.

At work we buy 100uF 25 volt caps in bags of 1000 and have so far
installed 2500 in 20 year old gear, mostly Sony. But we also have some
Ampex 2" quad machines built in 1978 with _all_ the orignal
electrolytics and the machines are in cherry condition. 30 years is
not necessarily the end point for caps.


Replace *all* of the electrolytics and move on. They're
*all* bad. Parts are cheap.

I replaced all the electro caps less than two years ago. Amp worked
fine up until
now. Polarity was and is correct. After cap blew today, new
replacement cap over
heated. I shut off power before it blew out.

What do you see with a scope? Something definitely funny going on. Is
the transformer heating up too?




BTW, if your question had been about repeated failures,
the diagnosis would be: the cap got too hot. It got too
hot because it was defective, or it was exposed to too
high a voltage,

I checked voltage across cap terminals with cap out. It read
correctly.

or it was exposed to reverse voltage,

Trust me. Polarity was correct.

or it was cooked by ESR.

Equivalent series resistance? Is that a measure of quality?

Oh yeah, ESR is a big deal.


Caps are no-names, both from the same parts house. hmm...


For little ( 1-4700 uF) caps we were using Panasonic FC series but
after reading some Hydrogenaudio forum posts, I found that the FM
series caps are even lower in ESR, longer llife (2000 vs 1000 hrs at
105 C) and they cost a little less. ($57.54 vs $61 / 1000 for 100uF
25V)


So, for future troubleshooting, eliminate these four
and you'll have only a mystery remaining!



Good fortune,
Chris Hornbeck

Definitely want to hear how this shakes out.

G²

[DC[_3_]]

"Tiger Luck" wrote in message
...
snip
Caps are no-names, both from the same parts house. hmm...
snip


Well, this may not be your problem, but things have deteriorated in the
electronic component area over the last few years. Many manufacturers have
out sourced production to China. Most if not all capacitor failures I have
seen in recent years have made in China - or no brand. Try to find something
that says made in Japan!!

Cheers

Dave

[William Sommerwerck]

I replaced all the electro caps less than two years ago. Amp
worked fine up until now. Polarity was and is correct. After
cap blew today, new replacement cap over heated. I shut off
power before it blew out.

It's remotely possible the replacement was defective. If the voltage across
the cap's location is correct in level and polarity, then that can't be the
problem.

Question... How safe is it -- other than the cap blowing -- to operate the
amp? I think you need to put a 'scope on a number of points and see what's
happening.

I don't mean to hassle you on the question of polarity, but... Japanese caps
generally have a black line on one side pointing toward the negative lead.

[Kevin McMurtrie[_2_]]

In article ,
Tiger Luck wrote:

For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the far
lower
right of the schematic, just above the separate, isolated schematic of the 15
volt
regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the cap
was
correct. The corresponding cap in the other channel does not blow. Both caps
have
the negative connected to the same source from the power supply and both have
their
positives connected to ground. In other words, the negs of both caps are
connected
together to the negative rail from the power supply and both positives are
grounded,
yet one cap blows and the other doesn't. The cap blew with a sharp crack and
the
rubber plug at the bottom blew out. The cap that blew is not shorted. It
still acts
like a cap should when measured with an analog ohm meter. I installed
another, new
cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?

Part of the circuit might have failed so that it oscillates or pulses.
For example - R313, C305, D301, C309, R335, or any of that bias circuit.
Drag the leads of a big foil capacitor across the leads of C313. It
should spark once to charge it. If it keeps sparking (or smokes),
there's AC current there.

The great thing about stereo amps is that you can put a voltmeter
between the matching parts of each side to find faults.

--
Google is a pro-spamming service. I will not see your reply if you use Google.

[Franc Zabkar]

On Wed, 10 Sep 2008 18:29:26 -0700, Tiger Luck
put finger to keyboard and composed:

For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the far lower
right of the schematic, just above the separate, isolated schematic of the 15 volt
regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the cap was
correct. The corresponding cap in the other channel does not blow. Both caps have
the negative connected to the same source from the power supply and both have their
positives connected to ground. In other words, the negs of both caps are connected
together to the negative rail from the power supply and both positives are grounded,
yet one cap blows and the other doesn't. The cap blew with a sharp crack and the
rubber plug at the bottom blew out. The cap that blew is not shorted. It still acts
like a cap should when measured with an analog ohm meter. I installed another, new
cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?

Maybe the trace from that channel to the -22V rail is partially open
(ie resistive), allowing C313 to be reverse charged from the +22V rail
via Q317 ???

Just for testing purposes, try running two hookup wires between the
caps in both channels.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

[Arfa Daily]

"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the
far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not blow.
Both caps have the negative connected to the same source from the power
supply and both have their positives connected to ground. In other words,
the negs of both caps are connected together to the negative rail from the
power supply and both positives are grounded, yet one cap blows and the
other doesn't. The cap blew with a sharp crack and the rubber plug at the
bottom blew out. The cap that blew is not shorted. It still acts like a
cap should when measured with an analog ohm meter. I installed another,
new cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two

In many years of repairing this stuff, and replacing electrolytics that have
failed any way from passively to explosively, I have only ever found three
things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail, and
the one for the other channel, which is also connected to the same place for
all intents and purposes, it's hard to see how there could be excessive ac
across one of them on its own. Have you tried running the amp without the
offending cap in ? It should almost certainly run normally without it, as
small caps in that position are usually just for 'belt and braces'
decoupling purposes.

I know that you have stated several times that the cap is in correctly, but
are you *absolutely totally completely and without question* sure ? Noted
that you replaced the caps a couple of years back and have not had trouble
in the intervening period, but that is not necessarily an indication that
all was well. I have seen equipment where caps have been fitted backwards by
the manufacturers, and have lasted a long time before finally failing. If
you are basing your latest replacements which are failing, on the way you
took out the first failed one - or even based on the way that the board is
marked, because I've seen them silkscreened backwards as well - I would say
please check very very carefully, go away and have a cup of coffee, then
come back and check again. It's easy to convince yourself that you are
seeing something you actually aren't. It has happened to me many times over
the years ...

I too would like to know what you eventually find, as the circumstances you
are describing are a bit of a conundrum. If it does come down to something
you have done, please tell us. I'm sure no-one will think any the less of
you. If we're honest, we've all been there d;~}

Arfa

[Mark D. Zacharias[_3_]]

"Arfa Daily" wrote in message
...

"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter
cap connecting the negative rail in the lower channel to ground. It is on
the far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not
blow. Both caps have the negative connected to the same source from the
power supply and both have their positives connected to ground. In other
words, the negs of both caps are connected together to the negative rail
from the power supply and both positives are grounded, yet one cap blows
and the other doesn't. The cap blew with a sharp crack and the rubber
plug at the bottom blew out. The cap that blew is not shorted. It still
acts like a cap should when measured with an analog ohm meter. I
installed another, new cap of equal value and it started heating up, so I
cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two

In many years of repairing this stuff, and replacing electrolytics that
have failed any way from passively to explosively, I have only ever found
three things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail,
and the one for the other channel, which is also connected to the same
place for all intents and purposes, it's hard to see how there could be
excessive ac across one of them on its own. Have you tried running the amp
without the offending cap in ? It should almost certainly run normally
without it, as small caps in that position are usually just for 'belt and
braces' decoupling purposes.

I know that you have stated several times that the cap is in correctly,
but are you *absolutely totally completely and without question* sure ?
Noted that you replaced the caps a couple of years back and have not had
trouble in the intervening period, but that is not necessarily an
indication that all was well. I have seen equipment where caps have been
fitted backwards by the manufacturers, and have lasted a long time before
finally failing. If you are basing your latest replacements which are
failing, on the way you took out the first failed one - or even based on
the way that the board is marked, because I've seen them silkscreened
backwards as well - I would say please check very very carefully, go away
and have a cup of coffee, then come back and check again. It's easy to
convince yourself that you are seeing something you actually aren't. It
has happened to me many times over the years ...

I too would like to know what you eventually find, as the circumstances
you are describing are a bit of a conundrum. If it does come down to
something you have done, please tell us. I'm sure no-one will think any
the less of you. If we're honest, we've all been there d;~}

Arfa


The matching cap on the other channel may now be open, thus not exploding
from a shorted rectifier in the power supply putting AC across the cap,
which would explain the original cap failure also, and would also go a long
way toward explaining the heating on the other channel.

The multiple failure does suggest to me that you are getting AC to that
negative rail. This would explain the voltage regulator failure, and I'll
bet the main transformer is getting hot as well.

More than once I've been misled by DC voltages only to find that it was an
AC problem, either line-related or HF oscillation.

Wouldn't be surprised if the main filter on that negative rail were bad also
(or maybe it just hasn't exploded yet from the AC !).

Too bad the schematic is not complete - I would have liked to have a full
PDF on this model.


Mark Z.

[Tiger Luck]

Mark D. Zacharias wrote:
"Arfa Daily" wrote in message
...
"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter
cap connecting the negative rail in the lower channel to ground. It is on
the far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not
blow. Both caps have the negative connected to the same source from the
power supply and both have their positives connected to ground. In other
words, the negs of both caps are connected together to the negative rail
from the power supply and both positives are grounded, yet one cap blows
and the other doesn't. The cap blew with a sharp crack and the rubber
plug at the bottom blew out. The cap that blew is not shorted. It still
acts like a cap should when measured with an analog ohm meter. I
installed another, new cap of equal value and it started heating up, so I
cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two
In many years of repairing this stuff, and replacing electrolytics that
have failed any way from passively to explosively, I have only ever found
three things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail,
and the one for the other channel, which is also connected to the same
place for all intents and purposes, it's hard to see how there could be
excessive ac across one of them on its own. Have you tried running the amp
without the offending cap in ? It should almost certainly run normally
without it, as small caps in that position are usually just for 'belt and
braces' decoupling purposes.

I know that you have stated several times that the cap is in correctly,
but are you *absolutely totally completely and without question* sure ?
Noted that you replaced the caps a couple of years back and have not had
trouble in the intervening period, but that is not necessarily an
indication that all was well. I have seen equipment where caps have been
fitted backwards by the manufacturers, and have lasted a long time before
finally failing. If you are basing your latest replacements which are
failing, on the way you took out the first failed one - or even based on
the way that the board is marked, because I've seen them silkscreened
backwards as well - I would say please check very very carefully, go away
and have a cup of coffee, then come back and check again. It's easy to
convince yourself that you are seeing something you actually aren't. It
has happened to me many times over the years ...

I too would like to know what you eventually find, as the circumstances
you are describing are a bit of a conundrum. If it does come down to
something you have done, please tell us. I'm sure no-one will think any
the less of you. If we're honest, we've all been there d;~}

Arfa


The matching cap on the other channel may now be open, thus not exploding
from a shorted rectifier in the power supply putting AC across the cap,
which would explain the original cap failure also, and would also go a long
way toward explaining the heating on the other channel.

The multiple failure does suggest to me that you are getting AC to that
negative rail. This would explain the voltage regulator failure, and I'll
bet the main transformer is getting hot as well.

More than once I've been misled by DC voltages only to find that it was an
AC problem, either line-related or HF oscillation.

Wouldn't be surprised if the main filter on that negative rail were bad also
(or maybe it just hasn't exploded yet from the AC !).

Too bad the schematic is not complete - I would have liked to have a full
PDF on this model.


Mark Z.

Mark, here is the other PDF. It includes the power supply and the tuner:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

Here are two sites devoted to this receiver. Schematics came from the latter:

http://home.netcarrier.com/%7Erstevens/advent.html
http://www.davidreaton.com/Model_300..._main_page.htm



--
Einstein forgot to carry the two

[William Sommerwerck]

I was partly right once, so perhaps the luck (ahem) will continue.

Barring a bad part, it sounds -- as someone else suggested -- that there's
something wrong with the board, or a solder joint.

Lemme tell you a story...

Back in 1980, I assembled an Integrex kit and had problems with one of the
op amps overheating. I spend almost an hour checking voltages, resistances,
etc, trying to figure out exactly what was causing the problem.

It then occurred to me to turn the board over and look carefully. Viola! Two
traces had a solder bridge. (Integrex was cheap and didn't provide a solder
mask.)

[Eeyore]

Arfa Daily wrote:

In many years of repairing this stuff, and replacing electrolytics that have
failed any way from passively to explosively, I have only ever found three
things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on.

An HF fault causing high local ripple ?

Graham

[Tiger Luck]

Arfa Daily wrote:
"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the
far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not blow.
Both caps have the negative connected to the same source from the power
supply and both have their positives connected to ground. In other words,
the negs of both caps are connected together to the negative rail from the
power supply and both positives are grounded, yet one cap blows and the
other doesn't. The cap blew with a sharp crack and the rubber plug at the
bottom blew out. The cap that blew is not shorted. It still acts like a
cap should when measured with an analog ohm meter. I installed another,
new cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two

In many years of repairing this stuff, and replacing electrolytics that have
failed any way from passively to explosively, I have only ever found three
things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail, and
the one for the other channel, which is also connected to the same place for
all intents and purposes, it's hard to see how there could be excessive ac
across one of them on its own. Have you tried running the amp without the
offending cap in ? It should almost certainly run normally without it, as
small caps in that position are usually just for 'belt and braces'
decoupling purposes.

I know that you have stated several times that the cap is in correctly, but
are you *absolutely totally completely and without question* sure ? Noted
that you replaced the caps a couple of years back and have not had trouble
in the intervening period, but that is not necessarily an indication that
all was well. I have seen equipment where caps have been fitted backwards by
the manufacturers, and have lasted a long time before finally failing. If
you are basing your latest replacements which are failing, on the way you
took out the first failed one - or even based on the way that the board is
marked, because I've seen them silkscreened backwards as well - I would say
please check very very carefully, go away and have a cup of coffee, then
come back and check again. It's easy to convince yourself that you are
seeing something you actually aren't. It has happened to me many times over
the years ...

I too would like to know what you eventually find, as the circumstances you
are describing are a bit of a conundrum. If it does come down to something
you have done, please tell us. I'm sure no-one will think any the less of
you. If we're honest, we've all been there d;~}

Arfa

Arfa, an update as requested and as promised.

First, a repost of my reply to William Sommerwerck posted today, 9/11/08 at 2:11pm
so that everything is in one post:
----------------------------------

Both output pairs are pulled.

I am reading 20 volts AC to ground on each of the stepped down leads from the
transformer and 40 volts AC between them.

The positive rail is reading 26.3 volts DC to ground and the negative rail is
reading 26.7 volts DC to ground after going through the bridge rectifier and the
filter caps. They are reading 53 volts between them. The replacement for the electro
cap that blew is reading 26.7 volts across its terminals. It connects the negative
rail to ground. Positive side is grounded. It is no longer heating up when power is on.

With power on and about to take some voltage readings across the empty output tranny
terminals on the CB, I noticed some tiny sparking going on at the edges of the trace
leading to the collector terminal of Q317, with occasional tiny puffs of smoke (see
schematics):

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

I removed as much solder as possible from the traces around all output terminals
with a solder wick and cleaned up the board with switch cleaner. Sparking appears to
have stopped.

Began taking various voltage measurements at same points in right and left channels.
Discovered huge variation on voltage across C-E terminals with output transistors
removed. Right side had about 26 to 27 volts across the C-E terminals of each
output transistor. The left side had no voltage across C-E terminals of one output
transistor and about 52 to 54 volts across the C-E terminals of the other output
transistor.

Also had different readings across C-E terminals of the two pairs of differential
transistors at the input. Right side had about 26-27 volts across C-E terminals of
each transistor and the left side had about 7 volts across the same terminals.
Disconnecting the base of Q302 resulted in both differential transistors on the left
reading identical to the right side across the C-E terminals. I traced it down to
where D304 connects to the base of Q302 thru a 20K resistor, R336. I reconnected the
base of Q302 and disconnecting the cathode side of D304 and got the same results as
disconnecting the base of Q302. Now it's just a matter of going through the same
procedure until I find the faulty component.

Disconnecting the base of Q302 had no effect on the voltage measurements of the
output transistors in the left channel, but disconnecting D304 did. Reading across
the C-E terminals of one output tranny on the right channel with D304 disconnected,
the digital meter read about 27 volts and then began drifting steadily lower,
similar to reading a large cap with an ohmmeter. When I switched the meter to the
C-E terminals of the other output tranny on the right side, it read higher than 27
volts by as much as the first tranny's voltage diminished when it was read.

And that's where it stands. Sorry for not reading and replying to every post, but
when I got enough insight from what I did read to see where I needed to go, I
stopped reading and went to work. Will report all findings and methods used.
--------------------------------------

Update:

Narrowed down the search to the upper section of the right channel as seen on the
schematics at the link above. Following the logic outlined above, I reconnected
everything and disconnected the base of Q308 and turned the power on to check
voltages discrepancies outlined above. With the unit on its side and probing the
underside of the circuit board, smoke began rising from the top side opposite me. I
cut power and found the following fried components:

Q308
Q310
R326
R328
R324

Pulled all the fried components and checked. Q308, Q310, R326 and R328 were toast
and I replaced them. R324 was still good, but replaced it. Everything except the
output trannies are in place and the voltage discrepancies between the two channels
have disappeared. I will now install the output trannies and give it a go.


--
Einstein forgot to carry the two

[Tiger Luck]

Tiger Luck wrote:
Arfa Daily wrote:
"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the
far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not blow.
Both caps have the negative connected to the same source from the power
supply and both have their positives connected to ground. In other words,
the negs of both caps are connected together to the negative rail from the
power supply and both positives are grounded, yet one cap blows and the
other doesn't. The cap blew with a sharp crack and the rubber plug at the
bottom blew out. The cap that blew is not shorted. It still acts like a
cap should when measured with an analog ohm meter. I installed another,
new cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two
In many years of repairing this stuff, and replacing electrolytics that have
failed any way from passively to explosively, I have only ever found three
things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail, and
the one for the other channel, which is also connected to the same place for
all intents and purposes, it's hard to see how there could be excessive ac
across one of them on its own. Have you tried running the amp without the
offending cap in ? It should almost certainly run normally without it, as
small caps in that position are usually just for 'belt and braces'
decoupling purposes.

I know that you have stated several times that the cap is in correctly, but
are you *absolutely totally completely and without question* sure ? Noted
that you replaced the caps a couple of years back and have not had trouble
in the intervening period, but that is not necessarily an indication that
all was well. I have seen equipment where caps have been fitted backwards by
the manufacturers, and have lasted a long time before finally failing. If
you are basing your latest replacements which are failing, on the way you
took out the first failed one - or even based on the way that the board is
marked, because I've seen them silkscreened backwards as well - I would say
please check very very carefully, go away and have a cup of coffee, then
come back and check again. It's easy to convince yourself that you are
seeing something you actually aren't. It has happened to me many times over
the years ...

I too would like to know what you eventually find, as the circumstances you
are describing are a bit of a conundrum. If it does come down to something
you have done, please tell us. I'm sure no-one will think any the less of
you. If we're honest, we've all been there d;~}

Arfa

Arfa, an update as requested and as promised.

First, a repost of my reply to William Sommerwerck posted today, 9/11/08 at 2:11pm
so that everything is in one post:
----------------------------------

Both output pairs are pulled.

I am reading 20 volts AC to ground on each of the stepped down leads from the
transformer and 40 volts AC between them.

The positive rail is reading 26.3 volts DC to ground and the negative rail is
reading 26.7 volts DC to ground after going through the bridge rectifier and the
filter caps. They are reading 53 volts between them. The replacement for the electro
cap that blew is reading 26.7 volts across its terminals. It connects the negative
rail to ground. Positive side is grounded. It is no longer heating up when power is on.

With power on and about to take some voltage readings across the empty output tranny
terminals on the CB, I noticed some tiny sparking going on at the edges of the trace
leading to the collector terminal of Q317, with occasional tiny puffs of smoke (see
schematics):

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

I removed as much solder as possible from the traces around all output terminals
with a solder wick and cleaned up the board with switch cleaner. Sparking appears to
have stopped.

Began taking various voltage measurements at same points in right and left channels.
Discovered huge variation on voltage across C-E terminals with output transistors
removed. Right side had about 26 to 27 volts across the C-E terminals of each
output transistor. The left side had no voltage across C-E terminals of one output
transistor and about 52 to 54 volts across the C-E terminals of the other output
transistor.

Also had different readings across C-E terminals of the two pairs of differential
transistors at the input. Right side had about 26-27 volts across C-E terminals of
each transistor and the left side had about 7 volts across the same terminals.
Disconnecting the base of Q302 resulted in both differential transistors on the left
reading identical to the right side across the C-E terminals. I traced it down to
where D304 connects to the base of Q302 thru a 20K resistor, R336. I reconnected the
base of Q302 and disconnecting the cathode side of D304 and got the same results as
disconnecting the base of Q302. Now it's just a matter of going through the same
procedure until I find the faulty component.

Disconnecting the base of Q302 had no effect on the voltage measurements of the
output transistors in the left channel, but disconnecting D304 did. Reading across
the C-E terminals of one output tranny on the right channel with D304 disconnected,
the digital meter read about 27 volts and then began drifting steadily lower,
similar to reading a large cap with an ohmmeter. When I switched the meter to the
C-E terminals of the other output tranny on the right side, it read higher than 27
volts by as much as the first tranny's voltage diminished when it was read.

And that's where it stands. Sorry for not reading and replying to every post, but
when I got enough insight from what I did read to see where I needed to go, I
stopped reading and went to work. Will report all findings and methods used.
--------------------------------------

Update:

Narrowed down the search to the upper section of the right channel as seen on the
schematics at the link above. Following the logic outlined above, I reconnected
everything and disconnected the base of Q308 and turned the power on to check
voltages discrepancies outlined above. With the unit on its side and probing the
underside of the circuit board, smoke began rising from the top side opposite me. I
cut power and found the following fried components:

Q308
Q310
R326
R328
R324

Pulled all the fried components and checked. Q308, Q310, R326 and R328 were toast
and I replaced them. R324 was still good, but replaced it. Everything except the
output trannies are in place and the voltage discrepancies between the two channels
have disappeared. I will now install the output trannies and give it a go.

Output trannies are back in. Speakers hooked up. Tuner tuned in.

Fingers crossed.

And here goes... power up... power down, got smoke.

Output trannies on the left side got hot, but held.

The drama continues. Will pull output trannies on left side and check right side for
okayness.

--
Einstein forgot to carry the two

[Tiger Luck]

Tiger Luck wrote:
Tiger Luck wrote:
Arfa Daily wrote:
"Tiger Luck" wrote in message
...
For the record, the amp is in an Advent 300, which I refuse to let die.

Here's a PDF of the schematics:

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

The cap that blows is C313. It is a 100mfd 35volt cap It is the filter cap
connecting the negative rail in the lower channel to ground. It is on the
far lower right of the schematic, just above the separate, isolated
schematic of the 15 volt regulator circuit.

The voltage on the negative rail is as it should be. The polarity of the
cap was correct. The corresponding cap in the other channel does not blow.
Both caps have the negative connected to the same source from the power
supply and both have their positives connected to ground. In other words,
the negs of both caps are connected together to the negative rail from the
power supply and both positives are grounded, yet one cap blows and the
other doesn't. The cap blew with a sharp crack and the rubber plug at the
bottom blew out. The cap that blew is not shorted. It still acts like a
cap should when measured with an analog ohm meter. I installed another,
new cap of equal value and it started heating up, so I cut the power.

I'm not a pro tech, but fairly knowledgeable and good at logic and such.

Any insights?



--
Einstein forgot to carry the two
In many years of repairing this stuff, and replacing electrolytics that have
failed any way from passively to explosively, I have only ever found three
things which cause their demise in the way you have described.

1) Excess voltage across them
2) Incorrect polarity of voltage across them
3) Excess current through them

3) is obviously the most difficult to diagnose, as it really requires a
'scope to see what's going on. However, given that this cap is effectively
in parallel with the main filter cap for the output stage negative rail, and
the one for the other channel, which is also connected to the same place for
all intents and purposes, it's hard to see how there could be excessive ac
across one of them on its own. Have you tried running the amp without the
offending cap in ? It should almost certainly run normally without it, as
small caps in that position are usually just for 'belt and braces'
decoupling purposes.

I know that you have stated several times that the cap is in correctly, but
are you *absolutely totally completely and without question* sure ? Noted
that you replaced the caps a couple of years back and have not had trouble
in the intervening period, but that is not necessarily an indication that
all was well. I have seen equipment where caps have been fitted backwards by
the manufacturers, and have lasted a long time before finally failing. If
you are basing your latest replacements which are failing, on the way you
took out the first failed one - or even based on the way that the board is
marked, because I've seen them silkscreened backwards as well - I would say
please check very very carefully, go away and have a cup of coffee, then
come back and check again. It's easy to convince yourself that you are
seeing something you actually aren't. It has happened to me many times over
the years ...

I too would like to know what you eventually find, as the circumstances you
are describing are a bit of a conundrum. If it does come down to something
you have done, please tell us. I'm sure no-one will think any the less of
you. If we're honest, we've all been there d;~}

Arfa
Arfa, an update as requested and as promised.

First, a repost of my reply to William Sommerwerck posted today, 9/11/08 at 2:11pm
so that everything is in one post:
----------------------------------

Both output pairs are pulled.

I am reading 20 volts AC to ground on each of the stepped down leads from the
transformer and 40 volts AC between them.

The positive rail is reading 26.3 volts DC to ground and the negative rail is
reading 26.7 volts DC to ground after going through the bridge rectifier and the
filter caps. They are reading 53 volts between them. The replacement for the electro
cap that blew is reading 26.7 volts across its terminals. It connects the negative
rail to ground. Positive side is grounded. It is no longer heating up when power is on.

With power on and about to take some voltage readings across the empty output tranny
terminals on the CB, I noticed some tiny sparking going on at the edges of the trace
leading to the collector terminal of Q317, with occasional tiny puffs of smoke (see
schematics):

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

I removed as much solder as possible from the traces around all output terminals
with a solder wick and cleaned up the board with switch cleaner. Sparking appears to
have stopped.

Began taking various voltage measurements at same points in right and left channels.
Discovered huge variation on voltage across C-E terminals with output transistors
removed. Right side had about 26 to 27 volts across the C-E terminals of each
output transistor. The left side had no voltage across C-E terminals of one output
transistor and about 52 to 54 volts across the C-E terminals of the other output
transistor.

Also had different readings across C-E terminals of the two pairs of differential
transistors at the input. Right side had about 26-27 volts across C-E terminals of
each transistor and the left side had about 7 volts across the same terminals.
Disconnecting the base of Q302 resulted in both differential transistors on the left
reading identical to the right side across the C-E terminals. I traced it down to
where D304 connects to the base of Q302 thru a 20K resistor, R336. I reconnected the
base of Q302 and disconnecting the cathode side of D304 and got the same results as
disconnecting the base of Q302. Now it's just a matter of going through the same
procedure until I find the faulty component.

Disconnecting the base of Q302 had no effect on the voltage measurements of the
output transistors in the left channel, but disconnecting D304 did. Reading across
the C-E terminals of one output tranny on the right channel with D304 disconnected,
the digital meter read about 27 volts and then began drifting steadily lower,
similar to reading a large cap with an ohmmeter. When I switched the meter to the
C-E terminals of the other output tranny on the right side, it read higher than 27
volts by as much as the first tranny's voltage diminished when it was read.

And that's where it stands. Sorry for not reading and replying to every post, but
when I got enough insight from what I did read to see where I needed to go, I
stopped reading and went to work. Will report all findings and methods used.
--------------------------------------

Update:

Narrowed down the search to the upper section of the right channel as seen on the
schematics at the link above. Following the logic outlined above, I reconnected
everything and disconnected the base of Q308 and turned the power on to check
voltages discrepancies outlined above. With the unit on its side and probing the
underside of the circuit board, smoke began rising from the top side opposite me. I
cut power and found the following fried components:

Q308
Q310
R326
R328
R324

Pulled all the fried components and checked. Q308, Q310, R326 and R328 were toast
and I replaced them. R324 was still good, but replaced it. Everything except the
output trannies are in place and the voltage discrepancies between the two channels
have disappeared. I will now install the output trannies and give it a go.

Output trannies are back in. Speakers hooked up. Tuner tuned in.

Fingers crossed.

And here goes... power up... power down, got smoke.

Output trannies on the left side got hot, but held.

The drama continues. Will pull output trannies on left side and check right side for
okayness.

Spoke too soon. Three of the output trannies fried and the fourth probably would
have if I had left the power on longer.

I have never given up on a piece of gear until now. It almost seems like the power
supply might be the problem seeing as how the outputs on both channels fried, but
who knows. It reads okay.

I've been at this thing for about four days straight now and I am totally fried
behind it. I've resurrected stuff the local vintage stereo store has given up on,
but this took me to my limits and left me out to dry.

If anyone wants this pup, with schematics, minus a couple of output trannies, for
the price of postage, email me at jack6128 at gmail dot com

Je suis fini.


--
Einstein forgot to carry the two

[William Sommerwerck]

I've been at this thing for about four days straight now and
I am totally fried behind it. I've resurrected stuff the local
vintage stereo store has given up on, but this took me to
my limits and left me out to dry.

Be patient. Put the unit aside for few days and come back to it. Don't
expect to solve every problem instantly. When your mind is fresh again,
you're likely to figure it out.

[Arfa Daily]

snip


Output trannies are back in. Speakers hooked up. Tuner tuned in.

Fingers crossed.

And here goes... power up... power down, got smoke.

Output trannies on the left side got hot, but held.

The drama continues. Will pull output trannies on left side and check
right side for okayness.

Spoke too soon. Three of the output trannies fried and the fourth probably
would have if I had left the power on longer.

I have never given up on a piece of gear until now. It almost seems like
the power supply might be the problem seeing as how the outputs on both
channels fried, but who knows. It reads okay.

I've been at this thing for about four days straight now and I am totally
fried behind it. I've resurrected stuff the local vintage stereo store has
given up on, but this took me to my limits and left me out to dry.

If anyone wants this pup, with schematics, minus a couple of output
trannies, for the price of postage, email me at jack6128 at gmail dot
com

Je suis fini.


--
Einstein forgot to carry the two

I do sympathise old boy. In years past, I never gave up on anything either,
but I must admit that these days, sometimes I do, out of both a need to be
commercial and keep the wife off my back for not earning any money, and out
of sheer frustration. I think that latter condition is something that creeps
up on you with age. Suddenly, some things are more important than not
letting some inanimate object beat you ...

That said, I reckon that this baby has got to be worth one more go if - and
*only* if - you can lay hands on a variac, so you can wind up the input
power to make the rails just high enough to take sensible measurements, but
low enough to stop the ouput trannies releasing their magic smoke ...

As William says, give it a break over the weekend, then come back to it with
fresh eyes (and a variac !!) on Monday. If you do, carry on keeping us
updated. It's an interesting saga, if a little frustrating for you.

Arfa

[Chris Hornbeck]

On Thu, 11 Sep 2008 17:51:45 -0700, Tiger Luck
wrote:


Spoke too soon. Three of the output trannies fried and the fourth probably would
have if I had left the power on longer.

Even a variac doesn't save output transistors in some cases
(but helps a lot in others).

An old-fashioned solution is to wire an incandescent
120 volt good old Edison lamp in series with the power
transformer's primary. Folks would wire up a contraption
with a lamp socket and male and female AC plugs/jacks.

The series lamp has two beauties: its cold resistance
is high enough to save some situations but its hot
resistance is higher, and can sometimes save others.
And, it gives a visual indication of current drain!


The other (and essential!) ingredient of amplifier trouble-
shooting is a current-vs.-voltage curve-tracer. This is
made with a single resistor, two test probes, a (usually 6 volts
or so) AC transformer as a signal source, and a dual-trace
X-Y-able scope.

The scope can be made from a computer sound card. Works
just fine at line frequency, and common grounds are not
an issue for this use.

With an I/V curve tracer, you simply walk your two test
probes through the (unpowered) circuit, observing and
comparing to experience and/or a known-good circuit.

Resistors look like a straight like of slope 1/R; diodes
(and transistors) look like an "L"; capacitors look like
elipses; etc. When you see something strange, you're in the
ballpark. Very fast and non-invasive.

I always include a couple of different resistor values,
switch selected for best inpedance match to the local
circuit. A K Ohm is a good middle value to begin with.


All good fortune, and don't give up. You have several
problems, probably lightning (overvoltage) related, but
they're all solvable.

Chris Hornbeck

[Eeyore]

Tiger Luck wrote:

Both caps have
the negative connected to the same source from the power supply and both have their
positives connected to ground. In other words, the negs of both caps are connected
together to the negative rail from the power supply and both positives are grounded,

Which is WRONG ! Read the diagram !

The negative of C311 should be grounded together with the POSITIVE of C313

Possibly a pcb legend error. I've known it happen.

Graham

[Franc Zabkar]

On Thu, 11 Sep 2008 13:51:27 +0100, Eeyore
put finger to keyboard and
composed:

Tiger Luck wrote:

Both caps have
the negative connected to the same source from the power supply and both have their
positives connected to ground. In other words, the negs of both caps are connected
together to the negative rail from the power supply and both positives are grounded,

Which is WRONG ! Read the diagram !

The negative of C311 should be grounded together with the POSITIVE of C313

Possibly a pcb legend error. I've known it happen.

Graham

The OP wrote that "the corresponding cap in the other *channel* [C312]
does not blow", not the other *rail*.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

[Ancient_Hacker]

if the -22 supply has failed, due to a blown diode or fuse, and if the
output transistors have shorted, then the -22 rail will be pulled
positive and that will blow the capacitor.

Also note that the schematic has errors on it, for instance the output
transistors have emitter and collectors reversed!

Hope you didnt wire the new ones in like the schematic!!

[[email protected]]

Ancient_Hacker wrote:
if the -22 supply has failed, due to a blown diode or fuse, and if
the
output transistors have shorted, then the -22 rail will be pulled
positive and that will blow the capacitor.

Also note that the schematic has errors on it, for instance the
output
transistors have emitter and collectors reversed!

Hope you didnt wire the new ones in like the schematic!!

I thought that at first too but if you zoom to 300% you'll see the
emitter marks where they belong and the 'squiggles' on the collectors
may be a 1970's version of heatsink. You'll see the same marks on the
collector of Q312 indicating it is thermally coupled to the heatsink
with the outputs.

Way back in the days when I worked on stereo gear I had a unit with
very bizarre distortion. It turned out to be a transistor with a
'leak' which on a curve tracer showed up as a transistor in parallel
with a resistor from E to C. If Tiger has a similar quirky part it may
explain why he's having such a bad time with that amp - which is
pretty straightforward and decent for it's day.

G²