A bit of concern about my JVC JA S77

jawasmell · Apr 16, 2014

Just thought I would take the lid off my amp today to spray all the switches, when I noticed the glue around the capacitors was wet and tacky, now I did see this glue before, but I was just going to leave it, but after seeing it wet I am not so sure, it all seems to have migrated for years. In picture two I have removed three components around it and cleaned the glue of, but it has stained the board. The two resisters and capacitor all measured perfect and in spec ESR and values are bang on. And there is no corrosion on any of the component leads.
Do you think there is a possibility of this shorting something out? I am seriously thinking of going over the whole amp and removing all the glue.
What would you do?

Binkman · Apr 16, 2014

greetings;

That's not glue. Leaking caps. If the amp was working then order new caps and clean up. Could do a out of circuit check on those transistors or replace and check the local resistors, too.

jawasmell · Apr 16, 2014

I took the cap out it wasn’t leaking and it measures a low esr and a perfect 100uf. Pretty sure it was the glue.

Robisme · Apr 16, 2014

Looks like possible corrosion on the resistor lead just under the cap. Pic 3

Reminds me of the corrosive Sansui glue.

Clean it up before it's an issue.

Rob

jawasmell · Apr 16, 2014

Yes I read a bit about the Sansui glue, I am not looking forward to this, the stuff is everywhere.

Binkman · Apr 16, 2014

Doesn't look like sansui glue patterns to me. If you've owned the amp since new I'll take your word for it. If not then how do you know if somebody replaced the caps and didn't bother with cleaning up.

If it is glue it must have one hell of a low melting point to spread like that. Acetone will clean the glue. Cotton ball and swab it on and let it soak in for 10 mins.

jawasmell · Apr 16, 2014

Would that not mean that every cap of a certain size and over, at one stage had leaked onto the board, and all the smaller caps by themselves never had a problem, I know your an expert and I respect that, and hope you would continue to help, but it does not seem likely. Also they all look like the original caps.
Please see the pictures of the rest of the boards. It was working before and no I have only had it about a month, but sounded like the volume and switches needed a clean.
Would the cleaner in the last picture be safe to use on the boards?
As I say the brown staining left from the glue seems impossible to remove which is really tripping out my o.c.d.

Ymir_Lifer · Apr 17, 2014

My JVC has it under the big 18000uf ELNA's but also 2 other places that aren't 'lytics. It looks very similar but is not wet or sticky, I think it might be glue. It does not appear to be leakage, at least I sure hope it's not....

Did you get cleaner on it and that's what made it sticky perhaps?

jawasmell · Apr 17, 2014

Nope this is before I did anything, it had not even been on for three weeks.

Ymir_Lifer · Apr 17, 2014

Hopefully some of the experienced repair gurus will recognize it and can give some more info, I'm definitely no expert. But logic should still come in handy here. Are all the brown spots gooey, and some dry? Do you see it anywhere that is not under an electrolytic cap? Like on mine where the board slots into the case. Can you see other visual evidence of cap failure, split or swollen cases? I will say that some of the puddles on yours look like resin and some look more like leaks. Perhaps 2 different events?

Really convenient if it is all glue, it sure looks like leaky 'lytics... Even where there are none... Damn now I'm wondering about my PS caps....

Did you use an ESR and C meter to check them or a DMM?

Binkman · Apr 17, 2014

To test if it's cap residue apply isopropyl alcohol to a swap. I use acetone or denatured alcohol (lacquer thinner) for glue.

I see a pattern here looking at the horizontal pics showing the running with those three caps. Wonder if the mfr got a bad batch of caps? You usually see that leakage with larger caps where these are what 35v typical?... where usually the sleeves shrink up or bulge at the tops for smaller caps.

Here's a shot courtesy of an unknown onliner took of a similar size cap.

http://www.audiokarma.org/forums/picture.php?albumid=3372&pictureid=23814

jawasmell · Apr 17, 2014

Robisme said:
Looks like possible corrosion on the resistor lead just under the cap. Pic 3

Reminds me of the corrosive Sansui glue.

Clean it up before it's an issue.

Rob

That resistor is R221 the book says 15K it measures 14.98K (picture 1)

X205 on the other hand does not look good (picture two and three)

Not sure how to measure this or what to replace it with either.

jawasmell · Apr 17, 2014

Ymir_Lifer said:
Hopefully some of the experienced repair gurus will recognize it and can give some more info, I'm definitely no expert. But logic should still come in handy here. Are all the brown spots gooey, and some dry? Do you see it anywhere that is not under an electrolytic cap? Like on mine where the board slots into the case. Can you see other visual evidence of cap failure, split or swollen cases? I will say that some of the puddles on yours look like resin and some look more like leaks. Perhaps 2 different events?

Really convenient if it is all glue, it sure looks like leaky 'lytics... Even where there are none... Damn now I'm wondering about my PS caps....

Did you use an ESR and C meter to check them or a DMM?

Only a couple of the brown spots are gooey, it is all localized around the bigger caps. All the cap bodies look to be in perfect condition.

Picture 1 and 2 show the results from measurements, of that capacitor on the volume board, that had the fluid round it. it is a 100uf 35v.

jawasmell · Apr 17, 2014

I could not test X201 because these two transistors are stuck together for some reason, so they would not physically fit into my meter without a lot of serious twisting. But I did measure X203 and it has a HFE off 192, whatever that means?
The picture below with most off the glue cleaned off, taking it section by section to reduce mistakes.

jawasmell · Apr 17, 2014

Link to what I have been using to clean with. Also very good with Nicotine.

ArctiClean

http://www.arcticsilver.com/arcticlean.htm

jawasmell · Apr 17, 2014

I do have a theory about this too, maybe this is a two part glue that was badly mixed during manufacture, resulting in not enough hardener being added, The effect of this, is glue that has been moving about for years, and never really hardening.
But this is just a guess of course and could just be wrong.

jawasmell · Apr 17, 2014

Binkman is acetone the same as nail varnish remover?, I have two daughters.
Will it remove the brown staining? Thanks everyone.

Ymir_Lifer · Apr 17, 2014

Unless it's 'acetone free' it usually has acetone in it, or is acetone.
The staining looks like it's probably absorbed in there pretty good though. Unless the resulting obsessive compulsions keep you up at night, just put the cover on and try not to let it get to you. :thmbsp:

Did that transistor clean up or were the leads burnt?

Looks like everything is probably fine. But again, no expert here.

I've never heard one of them before, but it sure looks cool.

jawasmell · Apr 18, 2014

O.K. I’m back now after being up all night working on the amp. Just kidding. I did manage to get most of it of the volume and tone board at least whatever could cause a potential hazard to the unit, added a before picture and then the rest are after, the staining is soaked into the board so that won’t come out, but it should be ok, now I did clean the green stuff of that transistor whether or not that is going to be fine I won't know yet but it was working before.

jawasmell · Apr 18, 2014

Do you think I should put some neutral cure silicon seal under those caps to replace the glue.

A bit of concern about my JVC JA S77

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