Analog board with Voltage too low then too high

#1 Mon, 7 Dec 2015 - 16:53 Analog board with Voltage too low then too high — #1

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 ?

#2 Mon, 7 Dec 2015 - 17:18 Analog board with Voltage too low then too high — #2

Try replacing the optocoupler or the two diodes nearby

#3 Mon, 7 Dec 2015 - 17:20 Analog board with Voltage too low then too high — #3

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

#4 Mon, 7 Dec 2015 - 19:01 Analog board with Voltage too low then too high — #4

Did you adjust it?

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

#5 Mon, 7 Dec 2015 - 19:54 Analog board with Voltage too low then too high — #5

Here:

Part number : CNY75GB

#6 Tue, 8 Dec 2015 - 16:36 Analog board with Voltage too low then too high — #6

Ok, thanks.