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Old 11th September 2005, 02:45 PM   #21
anatech is offline anatech  Canada
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Hi andjur78,
I've also seen that conductive glue. It is the cause of the corrosion as well. You should find that it will chip away for the most part. The plyable stuff needs to be cut and yanked out. I bet that's your problem.

I remove this whenever I see it. The darker brown it is, the lower the resistance tends to be.

-Chris
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Old 11th September 2005, 03:06 PM   #22
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I second all the comments on the brown glue.That stuff is bad news.It always causes me problems,especialy when it's old.
There's a similar yellowish kind I've seen a few times,but havn't noticed any problems with it (yet).
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Old 11th September 2005, 03:53 PM   #23
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I remember a similar fault in a big mixing console. Turned out it were the input caps.

/Hugo
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Old 12th September 2005, 02:21 AM   #24
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The caps dont actually look that bad. I have had seen the leaking (powdery) electros before, but these "look" ok. But when is a cap really a cap? Maybe these are cheap derrivitaves of the real electrolytic capacitor as we know (have known) it??
(I,m sure there would be a website dedicated to electro caps and brands out there somewhere)

I don't know exactly what that brown gunk is but it sure does show up in alot of audio gear that has been made in China .
All the AMC stuff I have seen over time uses this glue around the base of caps and Xtals. "Well done" for Welltronics!!
...maybe it is some kind of space age vegemite that astronaughts use on their sanwiches


Anyway,I will clean the pcb, replace all electros and reassemble it this week. Then its soak test time again.
Stand back...
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Old 12th September 2005, 12:11 PM   #25
anatech is offline anatech  Canada
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Hi andjur78,
The glue is used in PCB manufacture to hold the heavier components in place during soldering. I've seen it on Sony and NEC made PCB's as well. I think this is your only problem. Other components should be fine as long as the lead isn't corroded too much.

Someone once told me this wonderful stuff was called "Sonybond". I can't say for sure, but I know that Sony never admits to anything when they make a mistake.

-Chris
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Old 19th September 2005, 08:41 PM   #26
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Ok for all who are interested: It is not the caps!!!

I Replaced all electros, cleaned the pcb and went over every solder joint and the fault is still exhibited.

Now I will home in on the front end differential pair.

If anyone is interested in posts of the ongoing servicing of this amp please let me know and I will continue to post any updates.
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Old 19th September 2005, 08:58 PM   #27
anatech is offline anatech  Canada
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Hi andjur78,
Well, I'm always interested. I was hoping it was the "glue". That would be a cheap fix.

-Chris
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Old 19th September 2005, 09:03 PM   #28
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Quote:
Originally posted by anatech
Hi andjur78,
Well, I'm always interested.
-Chris
Me too as I was hoping for the caps. Up to the semiconductors.

/Hugo
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Old 19th September 2005, 09:57 PM   #29
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I am interested also....
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Old 19th September 2005, 11:55 PM   #30
anatech is offline anatech  Canada
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Should we start a pool? I guess it's too late now.

It looks like a junction breaking down in a transistor. Normally a 2SC458 is at the bottom of that, or an early J-fet. There are none of these here.

-Chris
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