Sharp GF555 one channel distortion signal when cold

[Kirill1012]

Hello everybody.

I am working on restoring Sharp GF555

So far I did the following :
1. Replaced ALL electrolytic capacitors in the entire unit
2. Re-soldered all connections
3. Replaced IC-104 (pre-amp unit)
4. disassembled, cleaned, verified resistance on ALL switches and slider potentiometers.
5. Measured resistance on printed circuit board built-in resistors.

Here is the issue I am facing :
When unit is cold, it produces distortion signal on only one channel (left). Once unit warms up the distortion disappears and the unit plays very well.
After unit is on for 15-20 minutes distortion signal disappears and if I turn it off and on again even with 2-3 hours intervals it works perfectly.

I tried freeze spray to identify the problematic area and no luck. I tried decoupling downstream components and could not find the issue.

Please share your ideas on how further to troubleshoot the issue.

Thank you so much everybody in advance.
Kirill.

 

[Superduper]

You did a lot of work, but provided no history as to why you did all that work. Were you trying to address a problem? Is the current issue also present before all the service? Also, does this unit have line-out? Can you confirm whether the distortion is present on the line-out too?

 

[Kirill1012]

You did a lot of work, but provided no history as to why you did all that work. Were you trying to address a problem? Is the current issue also present before all the service? Also, does this unit have line-out? Can you confirm whether the distortion is present on the line-out too?

Before I started to work on it the same issue was there. The unit has line out and my scope is also showing the distortion.

 

[Superduper]

Well, if you are using a scope, just work your way back along the signal path until you get to the source of your distortion, that is the most orderly and logical way to find your fault. If this was temperature related, freeze spray should work unless you aren't spraying in the correct spot.

 

[Kirill1012]

Well, if you are using a scope, just work your way back along the signal path until you get to the source of your distortion, that is the most orderly and logical way to find your fault. If this was temperature related, freeze spray should work unless you aren't spraying in the correct spot.

Thank you for the guidance,

I tried using scope to track down the signal but unfortunately there is a small window of opportunity for that. After 15 minutes unit warms up, signal disappears and I need to wait another 6-7 hours for it to appear again. I was hoping anyone had similar issue and can provide a clue which component/s
can be possible cause. Also freeze sprayed around IC104 preamp and on every transistor - hoping to catch microphonic effect - NOTHING.