Analog board with Voltage too low then too high

[bibilit]

I have been busy this week with a Classic II A/B.

Voltages were too low on the first place, so manage to replace the usual caps, but they remain low after the replacement.

On a second try those were far too high (5 volt was 6.25 v and 12 v around 12.2)

Any idea ?

 

[Ferrix97]

Try replacing the optocoupler or the two diodes nearby

 

[360alaska]

Did you adjust it? There should be a potentiometer:



Let's start there...

If you can't get a good result you can try to resolder PP1 and then replace the Optocoupler

 

[bibilit]

Did you adjust it?

No didn't touched it, can you advise where the Optocoupler is located ?

 

[360alaska]

Here:



Part number : CNY75GB

 

[bibilit]

Ok, thanks.

 

[bibilit]

Update,

Replaced the Optocoupler yesterday, and apart from a first boot when a cap bursted open (i realised i fitted it the wrong side) the AB board is working again.

Some weldings were a bit weak, and after touching those up, voltages are fine ans steady.