2. tech-talk
  3. 1357670498

Question for technicians

Recently I noticed my system was sounding dull and flat. Then I discovered there was little to no sound out of the right speaker, just an intermittent weak signal accompanied by static. Later, I noticed that I could make the signal come and go by merely touching the preamp's input selector switch, or applying a slight push-or-pull pressure to the control knob. I don't have any audio shops around here that I trust and I can do simple things like solder touch-up, continuity checks with a vom etc... Any ideas of how to go about checking this out? (greatly appreciate any and all advice)
rawinsonde
rawinsonde OP
47 posts
 
I bought a can of CRC (QD) Electronic Cleaner. I did this before seeing the last 3 posts as I figured this stuff was all basically the same thing.

After removing the knob with a small allen the shaft seemed to have no wiggle room going into the faceplate... extremely tight clearance. I sprayed liberally around the "opening" and worked the control back and forth hoping the cleaner would penetrate. On the other side of the faceplate (inside the chassis) the switch shaft goes into a housing of some sort where I can't get at it there.

When I hooked the preamp back up and tested it worked fine for a couple of days but now it is occasionaly failing again. Each time it fails I simple jiggle the selector to balance the sound again. But it only stays good for a while.

Since the cleaner did seem to have an effect, I guess I will repeat the same action with the cleaner, only work it more and for a longer time.

Any further ideas or suggestions? (thanks)
rx8man's avatar
rx8man
1,484 posts
 
Give it a shot with the preamp in a verticle position, working the input back and forth,
let sit over night.
atmasphere's avatar
atmasphere
12,055 posts
 
If you can't get to the switch itself then the cleaner is likely not going to do the job by trying to get it to go through the shaft bushing for the switch!

Your best option at this point is actually pretty simple- operate the switch vigorously to both limits about 50 times and see if it gives you any trouble after that. The only reason its a problem is corrosion from lack of operations.
rawinsonde OP
47 posts
 
Just for the record, I believe I said "selector" switch in an earlier post, but the faulty switch is actually the balance control (L to R) ... I'll try Atmasphere's vigorous attack method as that stuff seems to dry instantly and I doubt that it has any penetrating ability.
atmasphere's avatar
atmasphere
12,055 posts
 
I work on vintage electronics a lot. The better stuff frequently have 'J pots' in them- Allen Bradley J-Style potentiometers. They are really well sealed. If they get noisy, the technique above actually works fairly well on them unless they are really far gone. In that case you have to drill a small hole in them which is really dicy, but at least then you can clean them.
More to discover