[jim]

Hello all,
I have recently aqcuired a Sony TA-88 with a tuner from ebay.
As i have explained in the subject title, one of the internal fuses on
the brown wire, a 315mAT keeps blowing. At first I thought it would
just be an old fuse. Sometimes just after a few minutes. Sometimes
after a few hours, or even a days playing. I can see no dark areas on
the circuit boards or anything burnt, or smell anthing untoward from
the back.

I got my replacement fuses from Matalan, the box reads 630mA-6,3A then
a backward looking RU125V
on the other side of the box it reads, 10ESKA G-Sicherungseinsatze 250V
DIN EN 60127-2-3
and then handwritten over the top GL54

I have changed the power lead, (kettle type) - no difference.

Any advice would be nice.

Jim

[jim]

I have just opened the back to find that this time it was the fuse on
the white wire!!!
This is not evven consistant.
help please.....jim

[jim]

I have just opened the back to find that this time it was the fuse on
the white wire!!!
This is not evven consistant.
help please.....jim

[jim]

I have just opened the back to find that this time it was the fuse on
the white wire!!!
This is not evven consistant.
help please.....jim

[jim]

I have just replaced this fuse and left the cover off whlst it is
runing. i notice that the power light is flickering slightly now and
then. I have flexed the power lead at its fittings and there is no
difference, leading me to believe that the power lead is not to
fault.....jim

[jim]

I presume that putting in a higher tolerance fuse is not going to be a
good idea as it may burn something further along the way....jim

[Scott Dorsey]

jim wrote:
I have just opened the back to find that this time it was the fuse on
the white wire!!!

Honestly, this gear really isn't worth anyone's time to repair it. It's
designed to be disposable.

But if it were on my bench, I'd get the service manual, I would go through it
and look first for leaky electrolytic caps and then for biasing issues.
I am assuming you're blowing the low level fuses and not the fuses to
the output stage.

For the most part, anything from this era probably ought to have all the
electrolytic caps replaced proactively, before they all blow up. I won't
touch this stuff until I've shotgunned them all out to begin with.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

I presume that putting in a higher tolerance fuse is not going to be a
good idea as it may burn something further along the way....jim

You mean a higher-value fuse.

If you can find an AC ammeter, you should find out how much current the unit
is drawing.

[jakdedert]

jim wrote:
I presume that putting in a higher tolerance fuse is not going to be a
good idea as it may burn something further along the way....jim


No. You're over your head here. Some fault is making the fuses blow.
continuing to power that faulty component by replacing--even with the
proper-sized fuse--is likely causing further damage.

If you value this relic, stop now and take it to someone with some
technical expertise. You have demonstrated that you do not have the
qualifications.

jak

[jim]

very true perhaps, but you need to start somewhere. i don't suppose you
messed with devices as a child. not that i'm a child, some things need
to be dabbled before handing them over.

[jim]

hello scott
yes its the low level fuses which are blowing.
just had another look and I can not see any problems with the
capacitors, no bloating, leakage or any visible sign of anything
untoward.
I have not got access unfortunately to the service manual, i should
imagine its a fairly rare peice of literature.
I understand that this is old gear and was probably designed with its
lifes longevity in mind, but to look at it is a fantastic period
design. i did not buy it to thump out crazy decibels. just to sit and
play soft radio whilst being admired.
What else is there to look for or can be tested by the fearless novice?
Jim


Scott Dorsey wrote:
jim wrote:
I have just opened the back to find that this time it was the fuse on
the white wire!!!

Honestly, this gear really isn't worth anyone's time to repair it. It's
designed to be disposable.

But if it were on my bench, I'd get the service manual, I would go through it
and look first for leaky electrolytic caps and then for biasing issues.
I am assuming you're blowing the low level fuses and not the fuses to
the output stage.

For the most part, anything from this era probably ought to have all the
electrolytic caps replaced proactively, before they all blow up. I won't
touch this stuff until I've shotgunned them all out to begin with.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

What else is there to look for or can be tested by the fearless novice?

There's one other thing you might try...

Back in 1980 I had to repair a ReVox tape deck that was blowing fuses. There
was nothing wrong with the machine that I could find. However, I noticed
when I turned it on that the initial capacitor-charge surge caused the fuse
wire to expand. This weakened the wire, and after a few turn-ons, it broke.
I switched to a slo-blo-type fuse, and the problem stopped. The deck
continued to work properly, without further problems.

In short (no pun intended) -- the unit might have the wrong-type fuses.

[Scott Dorsey]

jim wrote:
hello scott
yes its the low level fuses which are blowing.

Okay, you need to find where the current is leaking.

just had another look and I can not see any problems with the
capacitors, no bloating, leakage or any visible sign of anything
untoward.

They are all bad. Every single one of them. They may not look bad,
but I guarantee not a single one of them meets factory spec.

I have not got access unfortunately to the service manual, i should
imagine its a fairly rare peice of literature.

It's not. Sony still has manuals in stock for their 1950s equipment.
They are very good at keeping manuals available. Call their manual
guys and order one.

I understand that this is old gear and was probably designed with its
lifes longevity in mind, but to look at it is a fantastic period
design. i did not buy it to thump out crazy decibels. just to sit and
play soft radio whilst being admired.
What else is there to look for or can be tested by the fearless novice?

You have something that is pulling more current than it should be. It
is either a bad cap or something misbiased. Since all the caps are probably
bad by now, I wouldn't touch the thing without shotgunning them all out
and replacing them with modern Panasonics. Then I'd rebias the output
stage, clean all the contracts with Cramolin and then burn it in for a
couple days and see if it's still blowing fuses. THEN I'd go one stage
at a time and measure voltages across emitter resistors and seeing that
they are in the ballpark with the voltages in the manual.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jim]

Thanks again scott
i have the two boards out again. The smaller board has 3 blue caps, all
about 1/2" and 3/4" long. There is also 8 smaller orange caps.
The larger board has 7 varied 1/2" to 3/4" blue caps and two large blue
ones. Both nearly 2" in length and 3/4" in diameter. These both have
25V and 2200uF stamped on the side.
I have a soldering iron and feel that I could replace any of these.
But i am not sure about biasing. forward-reverse, it all sound a bit to
do with flat green bowls to me. I did Modular technology at school,
making boards - deaf-mans doorbell and such like, but as someone
pointed out, to recognise when i am out of my depth is to admit defeat.
never.
Would replacing any/all of the capacitors be a good starting place?
Jim

[Scott Dorsey]

jim wrote:
Thanks again scott
i have the two boards out again. The smaller board has 3 blue caps, all
about 1/2" and 3/4" long. There is also 8 smaller orange caps.
The larger board has 7 varied 1/2" to 3/4" blue caps and two large blue
ones. Both nearly 2" in length and 3/4" in diameter. These both have
25V and 2200uF stamped on the side.

There are more than that in there. There should be a bunch of little
decoupling caps too. All you care about are the electrolytics... don't
worry about anything else.

I have a soldering iron and feel that I could replace any of these.

You will also need a solder-sucker, and some braid. You want a good hot
iron, not some 25W radio shack crap. You want to work hot and work fast.
Practice on some old PC power supply boards.

But i am not sure about biasing. forward-reverse, it all sound a bit to
do with flat green bowls to me. I did Modular technology at school,
making boards - deaf-mans doorbell and such like, but as someone
pointed out, to recognise when i am out of my depth is to admit defeat.

Okay, you can think of a transistor as being like a valve. It opens and
closes, allowing different amounts of current to flow through it, depending
on the current flowing into the base pin, which acts to control the valve.

If there is a transistor which has the incorrect static voltage on the base,
it will be turned on too much and pull too much current.

The service manual has a procedure for setting the bias for the output
stage, which is adjustable with a pot. Everything else is set with fixed
resistors, so if one transistor is pulling too much current you will have
to change a resistor or transistor to fix it.

Would replacing any/all of the capacitors be a good starting place?

Yes, you have to do that before you even begin to diagnose any of the
problems. If they are all radial types, try the Panasonic FC series
from Digi-Key. Digi-Key also carries the BC Components brand ASM021
and AML138 radials which are good substitutes.

You will need the service manual before doing anything. Call Sony and get
it. 816-891-7550 is what the number was a couple years ago.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jim]

Thanks once again Scott.
will get a better iron and have found this place http://www.heweb.co.uk
to get a service manual for £4.
Are the electrolytic caps all radial and are they signified by the blue
casing? I need not bother with the orange ones?
One step at a time, I will replace the capacitors and then start
thinking about which transistor is pulling too much power and if i need
to replace it or a resistor.
thanks for your time good man.
Jim


Scott Dorsey wrote:
jim wrote:
Thanks again scott
i have the two boards out again. The smaller board has 3 blue caps, all
about 1/2" and 3/4" long. There is also 8 smaller orange caps.
The larger board has 7 varied 1/2" to 3/4" blue caps and two large blue
ones. Both nearly 2" in length and 3/4" in diameter. These both have
25V and 2200uF stamped on the side.

There are more than that in there. There should be a bunch of little
decoupling caps too. All you care about are the electrolytics... don't
worry about anything else.

I have a soldering iron and feel that I could replace any of these.

You will also need a solder-sucker, and some braid. You want a good hot
iron, not some 25W radio shack crap. You want to work hot and work fast.
Practice on some old PC power supply boards.

But i am not sure about biasing. forward-reverse, it all sound a bit to
do with flat green bowls to me. I did Modular technology at school,
making boards - deaf-mans doorbell and such like, but as someone
pointed out, to recognise when i am out of my depth is to admit defeat.

Okay, you can think of a transistor as being like a valve. It opens and
closes, allowing different amounts of current to flow through it, depending
on the current flowing into the base pin, which acts to control the valve.

If there is a transistor which has the incorrect static voltage on the base,
it will be turned on too much and pull too much current.

The service manual has a procedure for setting the bias for the output
stage, which is adjustable with a pot. Everything else is set with fixed
resistors, so if one transistor is pulling too much current you will have
to change a resistor or transistor to fix it.

Would replacing any/all of the capacitors be a good starting place?

Yes, you have to do that before you even begin to diagnose any of the
problems. If they are all radial types, try the Panasonic FC series
from Digi-Key. Digi-Key also carries the BC Components brand ASM021
and AML138 radials which are good substitutes.

You will need the service manual before doing anything. Call Sony and get
it. 816-891-7550 is what the number was a couple years ago.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Scott Dorsey]

jim wrote:
Thanks once again Scott.
will get a better iron and have found this place http://www.heweb.co.uk
to get a service manual for =A34.
Are the electrolytic caps all radial and are they signified by the blue
casing? I need not bother with the orange ones?

I don't remember. It's been 25 years since I had one of those apart.
But if it's not a ceramic disc cap, it probably is an electrolytic and
needs to be replaced. Anything marked "electrolytic" or "tantalum" on
the parts list needs to go. If it's marked "ceramic," "mylar," "film"
or the like, it's probably okay.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Andre Majorel]

On 2007-01-23, jim wrote:

Are the electrolytic caps all radial

If it's a post-seventies device, probably.

and are they signified by the blue casing? I need not bother
with the orange ones?

For low voltages (10~35 V), if it's = 1 µF, it's probably an
electrolytic.

Radial electrolytics look like beer cans with two pins coming
out of the constricted end. If it's a box, a square plate, a
disc, it's probably not an electrolytic.

There are cylindrical caps that are NOT electrolytics. You can
tell because the can is transparent or opaque yellow plastic
molded around a roll of silvery film... And the capacity / size
ratio is much, much lower than for electrolytics. I reckon a 1
µF film cap would be about as big as a 10,000 µF electrolytic.

--
André Majorel URL:http://www.teaser.fr/~amajorel/
(Counterfeit: )
First rule of Usenet : if we don't have an answer, it's not a
good question.

[jim]

Hello again Scott,

I have bought a photocopied Service Manual for the Amp. Made in 1972,
a good year, my year of birth. It does not seem to mention anywhere
about setting the bias or how to test the flow to resistors and
transistors.

I can see where the power transistors are on the diagrams, there are
4. I could just replace these 4 if it would do it any good.

2 are described as: Driver transistors which operate as emitter-
followers to provide the current swings demanded at the output stages
and the necessary phase inversion. Phase inversion is performed by
using PNP and NPN type transistor.
The other two are the Power transistors connected directly to the
power supply of about +-23V. One supplies power to the load during the
positive half cycle and the other the negative. All stages are
directly coupled and are designed to obtain zero potential at the
output terminal. The large coupling capacitor at the output is
eliminated.

Please rephrase to me if you can.

I have noticed on the top of one cap there is a marker pen mark,
could this be the offending cap which has been replaced before now?
Doing this is maybe a way of showing to other sparkies that this has
been fettled with?

There is a list of components defining which are electrolytic caps
which will help.

I seem to remember having an earth strap from the unit to the bench
whilst working with electrics, is this going to be necessary, i
presume some of the caps will maintain a whack of voltage still,
before i go replacing and soldering anything what precautions need to
be made. Obviously i will not have it plugged in to the power supply!!

There is also a list of technical specifications, Dynamic Power,
RMS Power, Rated Power, etc.

Any more words of wisdom.

Jim

[Scott Dorsey]

jim wrote:

I have bought a photocopied Service Manual for the Amp. Made in 1972,
a good year, my year of birth. It does not seem to mention anywhere
about setting the bias or how to test the flow to resistors and
transistors.

No, all these things are on the schematic. Somewhere on the schematic
there is a voltage value across the emitter resistors. You adjust the
trimpots on the base of the output stage transistors to get the right
voltage value across the resistor.

I can see where the power transistors are on the diagrams, there are
4. I could just replace these 4 if it would do it any good.

No, invariably that will make any problems worse. If the output stage
isn't biased right, changing transistors will just change the bias point
it's set to, but probably not improve it.

2 are described as: Driver transistors which operate as emitter-
followers to provide the current swings demanded at the output stages
and the necessary phase inversion. Phase inversion is performed by
using PNP and NPN type transistor.
The other two are the Power transistors connected directly to the
power supply of about +-23V. One supplies power to the load during the
positive half cycle and the other the negative. All stages are
directly coupled and are designed to obtain zero potential at the
output terminal. The large coupling capacitor at the output is
eliminated.

Please rephrase to me if you can.

This is the standard output stage everybody has used for years and years
now. It is called a "push-pull amplifier" and it is discussed in a good
introduction to electronics (like Horowitz and Hill, or the ARRL Radio
Amateur's Handbook).

However, your problem isn't the output stage. If it were, you'd have
the output stage fuses blowing. The output stage _should_ be rebiased
as part of the usual service, but that's low on the priority list.

I have noticed on the top of one cap there is a marker pen mark,
could this be the offending cap which has been replaced before now?
Doing this is maybe a way of showing to other sparkies that this has
been fettled with?

Who knows? Is it the same brand cap? Invariably all the electrolytics
are going to be bad todey.

There is a list of components defining which are electrolytic caps
which will help.

That is important. And, of course, be sure to put them in the right
way.

I seem to remember having an earth strap from the unit to the bench
whilst working with electrics, is this going to be necessary, i
presume some of the caps will maintain a whack of voltage still,
before i go replacing and soldering anything what precautions need to
be made. Obviously i will not have it plugged in to the power supply!!

Not really. None of this stuff is as static sensitive as modern MOS
stuff. You should still touch something grounded before you sit down
and work, though.

There is also a list of technical specifications, Dynamic Power,
RMS Power, Rated Power, etc.

All these numbers come out of someone's ass in the marketing department
and can be freely ignored.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

You sure ask a lot of questions for someone from New Jersey, don't you?

It's good you have the service manual, but without someone who's
knowledgable about servicing equipment, it's going to be rough going.


I can see where the power transistors are on the diagrams, there
are 4. I could just replace these 4 if it would do it any good.

You can't just replace the output transistors on the assumption they're the
problem. The fact the amp works properly (other than blowing fuses) suggests
that they probably aren't the source of the problem. And if you did replace
the transistors, you'd probably have to rebias the driver and output stages,
which is not a task for someone with little service experience.

I'd suggest replacing all the electrolytic caps, particularly those in the
power supply. As these normally deteriorate over the years, "it couldn't
hurt". And you'll learn something about removing parts, soldering in the new
ones, etc.


2 are described as: Driver transistors which operate as emitter-
followers to provide the current swings demanded at the output stages
and the necessary phase inversion. Phase inversion is performed by
using PNP and NPN type transistor.

The other two are the power transistors connected directly to the
power supply of about +-23V. One supplies power to the load during
the positive half cycle and the other the negative. All stages are
directly coupled and are designed to obtain zero potential at the
output terminal. The large coupling capacitor at the output is
eliminated.

Please rephrase to me if you can.

They're simply saying this is a balanced circuit with no net DC at the
output -- hence, no output capacitor is needed to block the DC -- because
there isn't any that needs blockin. (If there were a net DC output, the
woofer would at the very least be offset, and at worst, damaged.)

[jim]

No, all these things are on the schematic. Somewhere on the
schematic
there is a voltage value across the emitter resistors. You adjust
the
trimpots on the base of the output stage transistors to get the right
voltage value across the resistor.

You're right sir, I have the schematic, the 'Emitter Follower' they
are described on the diagram show one side with -08V (-0.8V) and the
other with 12.5V.

To adjust using a trimpot would seem to be a problem. To be honest I
can not see one. I believe trimpots (from what i have seen) to be a
componant that can vary in shape, but all should have either a knob or
dial of some nature to adjust. All of the componants in this amp would
appear to be fixed. Is it possible it was not fitted with a trimpot?
or can a trimpot sometimes be a componant that you can bridge yourself
on a terminal? Then again, i presume as soon as you removed it, the
flow would return to its original flow rate.



I'm not sure where william got the idea that i was from New Jersey,
I'm from Wolverhampton, eclipsing London as the new 1st city in the
UK, the hub of all technology, similar to your silicon valley. The
central place to prosper and go wild like the osmonds song 'crazy
horses'. I take it people from New Jersey do not ask questions.

[William Sommerwerck]

To adjust using a trimpot would seem to be a problem. To be honest I
can not see one. I believe trimpots (from what i have seen) to be a
componant that can vary in shape, but all should have either a knob or
dial of some nature to adjust. All of the componants in this amp would
appear to be fixed. Is it possible it was not fitted with a trimpot?
or can a trimpot sometimes be a componant that you can bridge yourself
on a terminal? Then again, i presume as soon as you removed it, the
flow would return to its original flow rate.

I urge you not to start fooling with the output bias (other than checking
the voltage to see if it's correct), until you've determined why the unit is
blowing fuses. Replacing the electrolytics seems like a good first step in
restoring this unit.


I'm not sure where William got the idea I was from New Jersey...

It was one of Roseanne Rosannadanna's catchphrases: "You sure ask a lot of
questions for someone from New Jersey."

http://www.answers.com/topic/roseanne-roseannadanna

If you never saw the early SNLs, this won't mean much. Regardless, I meant
it as a joke. Nothing derogatory was intended.

[Deputy Dumbya Dawg]

"William Sommerwerck"
wrote in message news:EK-
:
: I'm not sure where William got the idea I was from
New Jersey...
:
: It was one of Roseanne Rosannadanna's catchphrases:
"You sure ask a lot of
: questions for someone from New Jersey."
:
: http://www.answers.com/topic/roseanne-roseannadanna
:
: If you never saw the early SNLs, this won't mean
much. Regardless, I meant
: it as a joke. Nothing derogatory was intended.

Hey:

roseanne-roseannadanna used to sit right behind me in
high school

Peace
Hernando-Roseannadando

[jim]

It's ok, no offence taken.

I have just gone to www.cpc.co.uk to order the replacement caps, I
noticed that there was a life expectancy listed next to each
componant. Mostly between 1000 & 2000 hours, this seems very short! I
sometimes leave the radio on in the house for days to keep the dog
company. At this rate I should imagine the device would only work for
a few weeks!

Unfortunately the Physics dept. at the University I work at no longer
has a lab. The IT guys are always too busy to get involved, so am
stuck on my own with this one.

I have just identified that the white wire 315mA fuse which was
blowing on the power supply board, bridges between the power
transformer and the voltage changeover block. Is all of this not prior
to the caps in the direction of current? Maybe the transformer is
faulty?

Jim

[William Sommerwerck]

I have just gone to www.cpc.co.uk to order the replacement caps,
I noticed that there was a life expectancy listed next to each
componant. Mostly between 1000 & 2000 hours, this seems very short! I
sometimes leave the radio on in the house for days to keep the dog
company. At this rate I should imagine the device would only work for
a few weeks!

You misread. It's 10000 hours, about 15 months.

And that's a ridiculous rating, anyway. Electrolytic caps can -- and do --
last for years, if not decades. Unless they're electrically abused (by
excessive voltage), their principal failure mode is drying out.

I don't know what sort of a company CPC is (anything like Radio Shack?), but
some of the prices look at bit on the high side. You might want to check
electronic-component wholesalers as well. (In the US, these are companies
such as Allied, MCM, Mouser, etc).

[Richard Crowley]

"jim" wrote ...
I have just gone to www.cpc.co.uk to order the replacement caps, I
noticed that there was a life expectancy listed next to each
componant. Mostly between 1000 & 2000 hours, this seems very short! I
sometimes leave the radio on in the house for days to keep the dog
company. At this rate I should imagine the device would only work for
a few weeks!

You are correct, those numbers are silly. Either you
read them wrong, or your source is incorrect. They
appear to be missing an order of magnitude (or 2).

Unfortunately the Physics dept. at the University I work at no longer
has a lab. The IT guys are always too busy to get involved, so am
stuck on my own with this one.

You are already in over your head without a service
manual, or AT LEAST a schematic diagram. No
competent technician would think of adjusting the
bias of an amplifier with no data.

I have just identified that the white wire 315mA fuse which was
blowing on the power supply board, bridges between the power
transformer and the voltage changeover block. Is all of this not prior
to the caps in the direction of current? Maybe the transformer is
faulty?

Much more likey something DOWNstream from the
fuse, not UPstream.

[Scott Dorsey]

jim wrote:

I have just gone to www.cpc.co.uk to order the replacement caps, I
noticed that there was a life expectancy listed next to each
componant. Mostly between 1000 & 2000 hours, this seems very short! I
sometimes leave the radio on in the house for days to keep the dog
company. At this rate I should imagine the device would only work for
a few weeks!

Those ratings are at the maximum temperature, and at normal temperatures
the capacitors will last far longer. But you should know that electrolytics
are rated specifically because they are items that fail and should be
considered wear items.

The Panasonic FC types that I recommended are designed for switching
supply use, and so have very good high frequency characteristics. They
are rated for 105'C use. The capacitor life drops dramatically with
operating temperature, so the higher the rating and the cooler you keep
them, the longer they will live.

Caps rated for 85'C use (which are probably what was originally in that
amp) will not last anywhere near as long as ones rated for 105'C use.
BCC/Philips makes some super-long-life and high temperature types as well,
but they are far more expensive.

I have just identified that the white wire 315mA fuse which was
blowing on the power supply board, bridges between the power
transformer and the voltage changeover block. Is all of this not prior
to the caps in the direction of current? Maybe the transformer is
faulty?

This is before _everything_. The power goes to the transformer, then to
the electronics. ANYTHING, ANYWHERE can cause that fuse to blow.

Transformers fail every once in a while, but hardly ever. Anything anywhere
in the circuit after the transformer will cause that fuse to blow.

Since you know all the caps in it are bad, that would be the first step.
Then I'd check the output stage bias, then break it in on the bench for
a couple days. If the fuse still blows, THEN it's time to do actual
diagnosis because THEN you have got yourself to the point where you can
actually do diagnosis.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jim]

Ok, well done all, i miss read it. 10,000 to 20,000 hours as you say.

I have ordered the caps. I had guessed about the temperature ratings
and ordered them as high as possible.

Unfortunately Panasonic only did some of the replacement caps, they
did not supply all at the ratings that were in there originally.

And Richard, I do have a Schematic and a Service Manual, if you read
through the history of this post, this is my first time dabbling at
this level. I understand that if i balls it up, there is nobody to
blame but myself (plus i have learned a bit along the way), but then
again, if it works, I will be a happy man. 'If yow dow ask questions,
yow aye gonna learn' - a classic Wolverhampton proverb.

To be honest, I am going to replace the caps & if the fuse still
blows, i may just leave it alone.

It makes sense that if you have a Trimpot, you can adjust something,
but if you don't, as in this case..... well it seems like leading a
blind man down a dark alley. Defeat is hard to swallow, but I may just
manage it, i can imagine some of the larger componants might be a
little hard without cutting them into smaller pieces.

[JohnO]

I have just identified that the white wire 315mA fuse which was
blowing on the power supply board, bridges between the power
transformer and the voltage changeover block. Is all of this not prior
to the caps in the direction of current? Maybe the transformer is
faulty?

Look in the other direction...that voltage changeover block...is it a
group of four diodes? On the schematic diodes will be black triangles
with lines at one point. If yes, that circuit is called a rectifier,
it converts the AC voltage into a variable DC voltage, which is made
into a nice and steady DC by the caps in that circuit. Those diodes
can get leaky and fail, allowing lots of current to flow...and blowing
fuses in the process. They're easy to test with an old analog
ohmmeter...google "test diodes". They're only slightly harder to test
with a digital meter.

-John O

[jim]

Thanks for the reply,
Yesterday i replaced all of the capacitors, fired it up, and within
10mins one of the fuses had blown again.The brown one. Doh!
Looking at the schematic, the fuses are prior to the bridge rectifier,
they are both between the voltage changeover block and the power
transformer. I have scanned in the diagram if anyone would care to
look.
As before, the power light on the front does seem to flicker
sometimes, giving me the impression that the power is not consistent.
Jim

[Scott Dorsey]

jim wrote:
Thanks for the reply,
Yesterday i replaced all of the capacitors, fired it up, and within
10mins one of the fuses had blown again.The brown one. Doh!

Okay, NOW you can start doing real diagnostic work. What is this "brown"
fuse, and does it go to the output stage or to the low-level stages?

Looking at the schematic, the fuses are prior to the bridge rectifier,
they are both between the voltage changeover block and the power
transformer. I have scanned in the diagram if anyone would care to
look.

Yes, this is the way all amplifiers are.

As before, the power light on the front does seem to flicker
sometimes, giving me the impression that the power is not consistent.

Does it flicker with signal level? If so, that usually indicates a
capacitor issue.

Now would be a good time to measure the voltages on the output stage and
see that they match up with the ones in the manual.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[William Sommerwerck]

Now would be a good time to measure the voltages on the output
stage and see that they match up with the ones in the manual.

And check the output bias -- indirectly -- by measuring the voltage across
the emitter resistors.

[JohnO]

On Feb 9, 9:31 am, "William Sommerwerck"
wrote:
Now would be a good time to measure the voltages on the output
stage and see that they match up with the ones in the manual.

And check the output bias -- indirectly -- by measuring the voltage across
the emitter resistors.


....IMO he should first seek out the power supply outputs and measure
each of them...then get back to us with the results. Just sayin, given
his experience level.

-John O

[jim]

Hello all,
This is just it, i may need a little more than ' this is the time to
diagnose'. The brown and the white (both with fuses) seem to both go
into the power transformer.
The brown goes via the power switch on the front. to the output or low
level, take your pick - the white does not seem to come out again.
I am going to to need some guidance to measure the the voltages, I
have a meter which would appear to measure Amps, Voltage, Ohms &
Continuity.
Like I say, please allow me to show you the Schematics if this enables
you to make a more informed direction. (spelling it out in pigeon
english for me as a simple man with limited knowledge of your field).
There are 8 other caps that have not been replaced on the preamp
board. All have been replaced on the power supply board.
thanks for your patience everyone.
Jim

[Scott Dorsey]

jim wrote:
There are 8 other caps that have not been replaced on the preamp
board. All have been replaced on the power supply board.

What are they and are they electrolytics?

I agree, you need to make sure all the caps are changed out, then check
the power supply voltages and make sure they agree with the ones on
the schematic, then check the output stage voltages and make sure they
also agree with the ones on the schematic.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[jim]

Anyone want to see the schematic? please send me your email address to
and i will forward a scanned version.

i am slightly nervous to start poking around in there trying the find
voltages with the power supply turned on. the last thing i want is to
fry something unnecessarily, and maybe myself in the process.

[JohnO]

On Feb 12, 10:07 am, "jim" wrote:
Anyone want to see the schematic? please send me your email address to
and i will forward a scanned version.

i am slightly nervous to start poking around in there trying the find
voltages with the power supply turned on. the last thing i want is to
fry something unnecessarily, and maybe myself in the process.


This is probably the time to find someone who can help in person. Your
safety is the most important thing. Telling you how to do something
like this, given your limited experience and your reluctance, isn't
such a good idea over the Internet.

You can certainly handle this if someone can *show* you how to do it
and be safe.

-John O

[jim]

I have a slightly different outlook today, ive got me rubber shoes on!
lets have it.

Jim

[William Sommerwerck]

Got your voltmeter? Following the schematic, measure the voltages. They
should be within 10% or so of the marked values.

Even more important, note the differences between voltages. For example,
most of the transistors show about 0.5V between the emitter (the arrow) and
the base. If the measured difference is not close, something is wrong.