[sdiy] Damned amplifier

[Lincoln Fong]

I recently visited my bro in NYC. He's developed a habit of buying old
70s receivers on Ebay and then sticking them in a closet when one side
inevitably cuts out. In each case the problem was the same. The source
or tape selector switch becomes tarnished. You can often tell by
wiggling it that it's at fault. I removed them one by one and carefully
took them apart cleaning all the contact bits with fine abrasive paper
though if I were in my workshop I'd use an abrasive pen. They all worked
after that. It's a bit of a pain with the desoldering but at least you
dont have to bother calling Sanyo or Rotel for a spare (hoho). One
seemed to get louder on one side until I realised that one side of the
Loudness switch was exhibiting the same problem.

I've also had dethump relay problems and if it has the type of headphone
socket that mutes the speakers it could easily be that, particularly a
joint gone bad on it's PCB. Also bad PCB joints to the input connectors.

Caps are notorious for the problem you mention but oddly I find they're
rarely the cause. I think their notoriety is somewhat exagerated.

Lincoln

-----Original Message-----
From: owner-synth-diy at dropmix.xs4all.nl
[mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf Of Linium
Sent: 11 November 2002 20:07
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Damned amplifier


Hello,

I have 2 stereo amplifiers that show almost the same faulty behaviors
and i 
would like to ask about this kind of problem.

The amplifier work ok but there are some moments where a voice start to
have 
some very short loss in the signal, like there is a bad contact
somewhere.

I have checked the connectors, the pots, and the boards, but it seems
that 
the problem is not coming from a mechanical defection. (and of course
not 
from the soundcard or the cable).

Do you now if there are some componants more than others likely to fail
that 
way ? works ok most of the time but then it will act like there is a bad

contact ?

I would be very very happy to learn more about this.

Linium