repairing a Parasound HCA-2200ii

[Robert Morein]

I just fixed my Parasound HCA-2200ii, a John Curl design, 225 wpc Class A up
to 6 watts.

A power rail bypass smoked, and took afew others with it. The rail bypass is
etched for a bunch of three caps in parallel, of indefinite size and shape.
It was populated with three tubulars, piggybacked with three low ESR "block"
film caps, three of each, varying between .01 and .2 ufd. One of the blocks
caught on fire, damaging two neighbors. While I had the amp apart, I found a
similar arrangement, deeper in circuitry; the tubular was smoked.

I called up Parasound. They didn't have anything like the originals,
offering instead to sell me .22ufd caps to make a wholesale replacement.
Anxious to see if the amp stil worked, I salvaged one undamaged cap off the
board, and reached into my junkbox for some old Cornell "CDR" yellow tubular
film caps. One of the low ESR caps on the bank survived. The amp now works
fine, and I really don't know if I'm missing anything or not.

What are opinions about the choice of caps? How do very old film caps, say
from the 70's, compare to modern low ESR caps? Should I take the amp apart
again and replace the bank with something "better" ?

[Richard Crowley]

"Robert Morein" wrote ...
>I just fixed my Parasound HCA-2200ii, a John Curl design, 225 wpc Class
>A up to 6 watts.
>
> A power rail bypass smoked, and took afew others with it. The rail
> bypass is etched for a bunch of three caps in parallel, of indefinite
> size and shape. It was populated with three tubulars, piggybacked with
> three low ESR "block" film caps, three of each, varying between .01
> and .2 ufd. One of the blocks caught on fire, damaging two neighbors.
> While I had the amp apart, I found a similar arrangement, deeper in
> circuitry; the tubular was smoked.
>
> I called up Parasound. They didn't have anything like the originals,
> offering instead to sell me .22ufd caps to make a wholesale
> replacement. Anxious to see if the amp stil worked, I salvaged one
> undamaged cap off the board, and reached into my junkbox for some old
> Cornell "CDR" yellow tubular film caps. One of the low ESR caps on the
> bank survived. The amp now works fine, and I really don't know if I'm
> missing anything or not.
>
> What are opinions about the choice of caps? How do very old film caps,
> say from the 70's, compare to modern low ESR caps? Should I take the
> amp apart again and replace the bank with something "better" ?

If it is power rail bypass capacitance, you can add as many
microfarads of whatever type you wish with virtual impugnity.
The ideal would be to have rock-solid rails that never move,
and the more capacitance you add, the closer you approach
the ideal.

I'd be tempted to poke the rails with an oscilloscope probe
and see how much droop or AC there was. (Not enough to
matter, I'd suspect.)

[Robert Morein]

"Richard Crowley" > wrote in message
...
> "Robert Morein" wrote ...
>>I just fixed my Parasound HCA-2200ii, a John Curl design, 225 wpc Class A
>>up to 6 watts.
>>
>> A power rail bypass smoked, and took afew others with it. The rail bypass
>> is etched for a bunch of three caps in parallel, of indefinite size and
>> shape. It was populated with three tubulars, piggybacked with three low
>> ESR "block" film caps, three of each, varying between .01 and .2 ufd. One
>> of the blocks caught on fire, damaging two neighbors. While I had the amp
>> apart, I found a similar arrangement, deeper in circuitry; the tubular
>> was smoked.
>>
>> I called up Parasound. They didn't have anything like the originals,
>> offering instead to sell me .22ufd caps to make a wholesale replacement.
>> Anxious to see if the amp stil worked, I salvaged one undamaged cap off
>> the board, and reached into my junkbox for some old Cornell "CDR" yellow
>> tubular film caps. One of the low ESR caps on the bank survived. The amp
>> now works fine, and I really don't know if I'm missing anything or not.
>>
>> What are opinions about the choice of caps? How do very old film caps,
>> say from the 70's, compare to modern low ESR caps? Should I take the amp
>> apart again and replace the bank with something "better" ?
>
> If it is power rail bypass capacitance, you can add as many
> microfarads of whatever type you wish with virtual impugnity.
> The ideal would be to have rock-solid rails that never move,
> and the more capacitance you add, the closer you approach
> the ideal.
>
I think that Curl's concern was that the speed of the capacitors is also
important. It's not simply a matter of capacity. This is why electrolytics
are frequently bypassed by small caps with low ESR.

[Sander deWaal]

"Robert Morein" > said:

>I think that Curl's concern was that the speed of the capacitors is also
>important. It's not simply a matter of capacity. This is why electrolytics
>are frequently bypassed by small caps with low ESR.


This used to be so.

Modern electrolytics, selected from a good brand low ESR 105 deg.
range, are so astoundingly good, that bypassing is IMHO not necessary.

Please do replace the remaining old capacitors, apparently they are
prone to shorting.

Measure the supply rails, due to a slowly rising mains voltage over
the years, they may be somewhat too high for the old caps.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

[Robert Morein]

"Sander deWaal" > wrote in message
...
> "Robert Morein" > said:
>
>>I think that Curl's concern was that the speed of the capacitors is also
>>important. It's not simply a matter of capacity. This is why electrolytics
>>are frequently bypassed by small caps with low ESR.
>
>
> This used to be so.
>
> Modern electrolytics, selected from a good brand low ESR 105 deg.
> range, are so astoundingly good, that bypassing is IMHO not necessary.
>
What about the old CDR tubular foil caps I used? How good are they?


> Please do replace the remaining old capacitors, apparently they are
> prone to shorting.
>
Apparently. The next time one shorts, I'll do the rest.


> Measure the supply rails, due to a slowly rising mains voltage over
> the years, they may be somewhat too high for the old caps.
>
Voltage here is stable at 112-113, measured with a Kill-A-Watt.

[Richard Crowley]

"Robert Morein" > wrote in message
...
>
> "Richard Crowley" > wrote in message
> ...
>> "Robert Morein" wrote ...
>>>I just fixed my Parasound HCA-2200ii, a John Curl design, 225 wpc
>>>Class A up to 6 watts.
>>>
>>> A power rail bypass smoked, and took afew others with it. The rail
>>> bypass is etched for a bunch of three caps in parallel, of
>>> indefinite size and shape. It was populated with three tubulars,
>>> piggybacked with three low ESR "block" film caps, three of each,
>>> varying between .01 and .2 ufd. One of the blocks caught on fire,
>>> damaging two neighbors. While I had the amp apart, I found a similar
>>> arrangement, deeper in circuitry; the tubular was smoked.
>>>
>>> I called up Parasound. They didn't have anything like the originals,
>>> offering instead to sell me .22ufd caps to make a wholesale
>>> replacement. Anxious to see if the amp stil worked, I salvaged one
>>> undamaged cap off the board, and reached into my junkbox for some
>>> old Cornell "CDR" yellow tubular film caps. One of the low ESR caps
>>> on the bank survived. The amp now works fine, and I really don't
>>> know if I'm missing anything or not.
>>>
>>> What are opinions about the choice of caps? How do very old film
>>> caps, say from the 70's, compare to modern low ESR caps? Should I
>>> take the amp apart again and replace the bank with something
>>> "better" ?
>>
>> If it is power rail bypass capacitance, you can add as many
>> microfarads of whatever type you wish with virtual impugnity.
>> The ideal would be to have rock-solid rails that never move,
>> and the more capacitance you add, the closer you approach
>> the ideal.
>>
> I think that Curl's concern was that the speed of the capacitors is
> also important. It's not simply a matter of capacity. This is why
> electrolytics are frequently bypassed by small caps with low ESR.

Go for it. Find some nice low ESR microwave-quality
chip caps and heat up your soldering iron.

[Richard Crowley]

"Robert Morein" wrote...

> What about the old CDR tubular foil caps I used? How good are they?

If you are that concerned about the electrolytics in your
equipment going bad, you might investigate getting a
capacitance/ESR meter. I believe there are some low-
cost (relatively) solutions.

[ScottW]

"Robert Morein" > wrote in message
...
>
> "Sander deWaal" > wrote in message
> ...
>> "Robert Morein" > said:
>>
>>>I think that Curl's concern was that the speed of the capacitors is also
>>>important. It's not simply a matter of capacity. This is why
>>>electrolytics
>>>are frequently bypassed by small caps with low ESR.
>>
>>
>> This used to be so.
>>
>> Modern electrolytics, selected from a good brand low ESR 105 deg.
>> range, are so astoundingly good, that bypassing is IMHO not necessary.
>>
> What about the old CDR tubular foil caps I used? How good are they?
>
>
>> Please do replace the remaining old capacitors, apparently they are
>> prone to shorting.
>>
> Apparently. The next time one shorts, I'll do the rest.
>

Personally, I wouldn't wait. A small electrolytic shorted in a printer
at work in a locked office and it took a while to figure out what that
stench
was and where it was coming from. One tiny cap and about 10,000
sq feet of office space stank for days.. and the office was unocuppiable
for over a week. It would be awful to have that happen at home.
BTW... the printer wasn't on... the power supply was always hot when
plugged in. No switch on the AC.
My kids Lexmark with a brick on back was the same way and that thing
melted on us but luckily didn't smoke.
I'm kind of surprised U/L lets em get away with that.
You leave the house for a few days and you think turning crap off is good
enough...think again.

ScottW

[Robert Morein]

"ScottW" > wrote in message
news:8ZgTf.138823$0G.62321@dukeread10...
>
> "Robert Morein" > wrote in message
> ...
>>
>> "Sander deWaal" > wrote in message
>> ...
>>> "Robert Morein" > said:
>>>
>>>>I think that Curl's concern was that the speed of the capacitors is also
>>>>important. It's not simply a matter of capacity. This is why
>>>>electrolytics
>>>>are frequently bypassed by small caps with low ESR.
>>>
>>>
>>> This used to be so.
>>>
>>> Modern electrolytics, selected from a good brand low ESR 105 deg.
>>> range, are so astoundingly good, that bypassing is IMHO not necessary.
>>>
>> What about the old CDR tubular foil caps I used? How good are they?
>>
>>
>>> Please do replace the remaining old capacitors, apparently they are
>>> prone to shorting.
>>>
>> Apparently. The next time one shorts, I'll do the rest.
>>
>
> Personally, I wouldn't wait. A small electrolytic shorted in a printer
> at work in a locked office and it took a while to figure out what that
> stench
> was and where it was coming from. One tiny cap and about 10,000
> sq feet of office space stank for days.. and the office was unocuppiable
> for over a week. It would be awful to have that happen at home.
> BTW... the printer wasn't on... the power supply was always hot when
> plugged in. No switch on the AC.
> My kids Lexmark with a brick on back was the same way and that thing
> melted on us but luckily didn't smoke.
> I'm kind of surprised U/L lets em get away with that.
> You leave the house for a few days and you think turning crap off is good
> enough...think again.
>
> ScottW
The electrolytics aren't the ones that smoked.
These are tiny film caps. They are dry. No odor was detected.

[ScottW]

"Robert Morein" > wrote in message
...
>
> "ScottW" > wrote in message
> news:8ZgTf.138823$0G.62321@dukeread10...
>>
>> "Robert Morein" > wrote in message
>> ...
>>>
>>> "Sander deWaal" > wrote in message
>>> ...
>>>> "Robert Morein" > said:
>>>>
>>>>>I think that Curl's concern was that the speed of the capacitors is
>>>>>also
>>>>>important. It's not simply a matter of capacity. This is why
>>>>>electrolytics
>>>>>are frequently bypassed by small caps with low ESR.
>>>>
>>>>
>>>> This used to be so.
>>>>
>>>> Modern electrolytics, selected from a good brand low ESR 105 deg.
>>>> range, are so astoundingly good, that bypassing is IMHO not necessary.
>>>>
>>> What about the old CDR tubular foil caps I used? How good are they?
>>>
>>>
>>>> Please do replace the remaining old capacitors, apparently they are
>>>> prone to shorting.
>>>>
>>> Apparently. The next time one shorts, I'll do the rest.
>>>
>>
>> Personally, I wouldn't wait. A small electrolytic shorted in a
>> printer
>> at work in a locked office and it took a while to figure out what that
>> stench
>> was and where it was coming from. One tiny cap and about 10,000
>> sq feet of office space stank for days.. and the office was unocuppiable
>> for over a week. It would be awful to have that happen at home.
>> BTW... the printer wasn't on... the power supply was always hot when
>> plugged in. No switch on the AC.
>> My kids Lexmark with a brick on back was the same way and that thing
>> melted on us but luckily didn't smoke.
>> I'm kind of surprised U/L lets em get away with that.
>> You leave the house for a few days and you think turning crap off is good
>> enough...think again.
>>
>> ScottW
> The electrolytics aren't the ones that smoked.
> These are tiny film caps. They are dry. No odor was detected.

No...but if something next to them did... they just got a bit cooked.

ScottW

[Robert Morein]

"ScottW" > wrote in message
news:VDhTf.138827$0G.80026@dukeread10...
>
> "Robert Morein" > wrote in message
> ...
>>
>> "ScottW" > wrote in message
>> news:8ZgTf.138823$0G.62321@dukeread10...
>>>
>>> "Robert Morein" > wrote in message
>>> ...
>>>>
>>>> "Sander deWaal" > wrote in message
>>>> ...
>>>>> "Robert Morein" > said:
>>>>>
>>>>>>I think that Curl's concern was that the speed of the capacitors is
>>>>>>also
>>>>>>important. It's not simply a matter of capacity. This is why
>>>>>>electrolytics
>>>>>>are frequently bypassed by small caps with low ESR.
>>>>>
>>>>>
>>>>> This used to be so.
>>>>>
>>>>> Modern electrolytics, selected from a good brand low ESR 105 deg.
>>>>> range, are so astoundingly good, that bypassing is IMHO not necessary.
>>>>>
>>>> What about the old CDR tubular foil caps I used? How good are they?
>>>>
>>>>
>>>>> Please do replace the remaining old capacitors, apparently they are
>>>>> prone to shorting.
>>>>>
>>>> Apparently. The next time one shorts, I'll do the rest.
>>>>
>>>
>>> Personally, I wouldn't wait. A small electrolytic shorted in a
>>> printer
>>> at work in a locked office and it took a while to figure out what that
>>> stench
>>> was and where it was coming from. One tiny cap and about 10,000
>>> sq feet of office space stank for days.. and the office was unocuppiable
>>> for over a week. It would be awful to have that happen at home.
>>> BTW... the printer wasn't on... the power supply was always hot when
>>> plugged in. No switch on the AC.
>>> My kids Lexmark with a brick on back was the same way and that thing
>>> melted on us but luckily didn't smoke.
>>> I'm kind of surprised U/L lets em get away with that.
>>> You leave the house for a few days and you think turning crap off is
>>> good
>>> enough...think again.
>>>
>>> ScottW
>> The electrolytics aren't the ones that smoked.
>> These are tiny film caps. They are dry. No odor was detected.
>
> No...but if something next to them did... they just got a bit cooked.
>
> ScottW
I agree. The one cap that burned took out two neighboring film caps, but no
electrolytics or other parts are in the vicinity.

[Sander deWaal]

"Robert Morein" > said:


>>>>> What about the old CDR tubular foil caps I used? How good are they?


Dunno, I'm not familiar with them.


>>>>>> Please do replace the remaining old capacitors, apparently they are
>>>>>> prone to shorting.


>>>>> Apparently. The next time one shorts, I'll do the rest.


Please do it soon.
Scott already told what can happen when a cap shorts.
A supply rail going down via a foil cap may damage your amp, and take
several other components with it.


>I agree. The one cap that burned took out two neighboring film caps, but no
>electrolytics or other parts are in the vicinity.


Well, there you have it.
You can never predict what a short will damage before the mains fuse
blows.

--

- Never argue with idiots, they drag you down their level and beat you with experience. -

[Arny Krueger]

"Robert Morein" > wrote in message


> What are opinions about the choice of caps? How do very
> old film caps, say from the 70's, compare to modern low
> ESR caps? Should I take the amp apart again and replace
> the bank with something "better" ?

As a rule the designers of modern caps have paid more attention than ever to
obtaining low ESR. A modern electrolytic cap probably has as low if not
lower ESR and series inductance than film caps made back in the 70s.

[Robert Morein]

"Sander deWaal" > wrote in message
...
> "Robert Morein" > said:
>
>
>>>>>> What about the old CDR tubular foil caps I used? How good are they?
>
>
> Dunno, I'm not familiar with them.
>
>
>>>>>>> Please do replace the remaining old capacitors, apparently they are
>>>>>>> prone to shorting.
>
>
>>>>>> Apparently. The next time one shorts, I'll do the rest.
>
>
> Please do it soon.
> Scott already told what can happen when a cap shorts.
> A supply rail going down via a foil cap may damage your amp, and take
> several other components with it.
>
The reason I'm not doing it is:
1. When I took the amp apart, I discovered a similar failure, but in an area
that was not clearly a rail bypass, that had gone unnoticed, for a total of
two.
2. This means that I would have to do every foil cap on the board. There are
quite afew. The amp works great.

One thing that might have provoked it is the use of a Parasound SCAMP
(signal controlled amplifier power). It senses the presence of audio, and
turns the power to the amp on and off. This one was glitching quite a bit,
rapidly turning the amp on/off at random intervals, due to noise from
computer switching supplies. I have since moved the audio to a separate
dedicated line. I speculate that the rapid cycling might have caused
inductive spikes from the collapse of the power transformer field. Or, the
life cycle on/off count may have been considerably exceeded.

This amp succeeded in incinerating two caps, and afew neighbors, with no
collateral damage where it hurts, ie., a transistor. Rather than rework the
board, I'll take my chances.

[Robert Morein]

"Arny Krueger" > wrote in message
...
> "Robert Morein" > wrote in message
>
>
>> What are opinions about the choice of caps? How do very
>> old film caps, say from the 70's, compare to modern low
>> ESR caps? Should I take the amp apart again and replace
>> the bank with something "better" ?
>
> As a rule the designers of modern caps have paid more attention than ever
> to obtaining low ESR. A modern electrolytic cap probably has as low if not
> lower ESR and series inductance than film caps made back in the 70s.
The Parasound was made in 1993.

[Arny Krueger]

"Robert Morein" > wrote in message


> "Arny Krueger" > wrote in message
> ...

>> "Robert Morein" > wrote in message
>>
>>
>>> What are opinions about the choice of caps? How do very
>>> old film caps, say from the 70's, compare to modern low
>>> ESR caps? Should I take the amp apart again and replace
>>> the bank with something "better" ?
>>
>> As a rule the designers of modern caps have paid more
>> attention than ever to obtaining low ESR. A modern
>> electrolytic cap probably has as low if not lower ESR
>> and series inductance than film caps made back in the
>> 70s.

> The Parasound was made in 1993.

It might have not needed special caps or not. John Curl is well known for
radical overbuilding.