Troubleshooting ISA 220

Hi there

I have acquired a used ISA 220 about 3 years ago.  Since a few weeks, the signal on the unit started to die randomly. No signalprocessing active, only using it as a preamp, the signal dies away in a not too loud farting-noise in about one second and the vu-meter isn't moving anymore. So i decided to open it up and have a look. What i discovered, are two bloated caps near the output xlr. their top isn't flat, but convex. you can't see it that well on the attached image, but they are the only ones looking like this on the whole pcb.

Now i am quite an amateur in troubleshooting electronics. I have built several microphones from poctop, kits from capi, soundskulptor, jlm etc.. all working flawlessly. but that's like putting together some lego, as you know.  So my questions are these:

- Should i replace only the two bloated caps and see, if the problems gone?
- Should i replace all the electrolytics, while i'm at it (around 100 electrolytics)? The unit might be around  15 years old...

Thanks for your help! Many regards, Joachim

I would definitely replace those 2 electrolytics as a starter.

Capacitors do not generally fail intermittent. I had one production run of caps where a broken swaging tool made a flaky foil to electrode connections and they were intermittent but that was an outlier and new caps fresh from the factory.

The symptoms sound more like a bad solder connection.

JR

Thanks for your replies! I'm going to replace those two caps and check the boards and switches for bad connections and report back.

I replaced caps in a focusrite red for a client. The unite was from 1999.  It had a number of problems but worked .  All issues were caused from caps .  I replaced power caps too but they tested ok.  The units problems with some eq bands not working correctly disappeared. The best thing was it sounded pristine , very noticeable improvement . There are about 50 by pass caps in that unit.  My test method was Using an ESR tester.  Client was extremely happy with the results. You need a desolder vacuume tool or you will ruin the traces.

Do you think of a desoldering tool ala Hakko or would a regular desoldering pump do? For the price of a Hakko station i can send the umit to Focusrite  ;D

I can see the caps failing as they do get hot in there.

Joekkel said:

Do you think of a desoldering tool ala Hakko or would a regular desoldering pump do? For the price of a Hakko station i can send the umit to Focusrite  ;D

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solder wick or solder suckers are cheap...

good training.

JR

circuit specialist has a nice desoldering gun for very economical prices.  I picked it up not long ago and I still use a desolder pump for things from time to time. I never had good luck with the desolder braid perhaps I am using it incorrectly but not applying enough heat

pucho812 said:

I never had good luck with the desolder braid perhaps I am using it incorrectly but not applying enough heat

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I like it....I use the kind with the flux in it??..chem-wik??..Saw someone here mention that and gave it a try.....

pucho812 said:

circuit specialist has a nice desoldering gun for very economical prices.  I picked it up not long ago and I still use a desolder pump for things from time to time. I never had good luck with the desolder braid perhaps I am using it incorrectly but not applying enough heat

Click to expand...

Solder wick is less harmful than cheap mechanical pump solder suckers can be to fragile PCB traces. Of course too much heat can damage PCBs with poor copper adhesion.

JR

Do you think of a desoldering tool ala Hakko

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.

There are some good manual pumps. I had a metal one that was great .  I can’t find it so I got a cheap one and it was terrible. 

Problem is it’s a 2 sided at least board so braid might pull from one side and not the other and so you now heat the other side until you burned the adhesion holding the trace .    I have a hakko and recommend it.  If you don’t get all the solder the first time just add solder and suck with the Hakko and it’s clean as a whistle .  There are other nice systems that can work but I own a lot of classic gear and you will ruin the traces if you try to replace 45 caps from a multilayered board.  You show 2 caps that look bad .  So try a hand pump devac and braid that has chemical flux and fix those 2 caps.  If you want to replace more ,  get an ESR tester and a Hakko or similar and turn a miserable job into a pleasant one.    I also replaced with nichion muse ultra audio caps .  My client was blown away by the sound of it after finishing.  There are other caps that sound good as well but I’m sold on the caps I got. 

fazer said:

  I also replaced with nichion muse ultra audio caps .  My client was blown away by the sound of it after finishing.  There are other caps that sound good as well but I’m sold on the caps I got. 

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I know those Muse KZ have fat leads that don't work in all pcbs... :-[

regardless of the tool you use, the most important thing is that the solder is flowing. Non-flowing solder and you will damage  things.  so proceed with caution.

pucho812 said:

regardless of the tool you use, the most important thing is that the solder is flowing. Non-flowing solder and you will damage  things.  so proceed with caution.

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Exactly. 

That’s why adding solder adds flux which allows it to flow instead of crystallized.

I know those Muse KZ have fat leads that don't work in all pcbs... :-[

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they are fat leads. I used Muse KA which have the smaller leads. 

hi everyone

i changed around 20 caps in the isa, around 5 were suspicious looking, the others sat around the psu-transistors. the bloated ones measured around 5uf when they should be 100uf. after some initial testing, the unit seems to work flawlessly again!

thanks everyone for your help. this forum rocks!

ps: about desoldering. i figured out, it works best, when i just heat the capacitors legs and pull them out and then use the desoldering pump to clean the holes. didn't damage any traces