Hello,
I recently bought a GPD-3303S power supply. The only known problems were a broken voltage rotary encoder which I've already fixed. It still has the known problem of CH3 overshoot described
here which I will fix at the same time as whatever outcome we discover here. The service manual with schematics
is available here.
The reason I think there is a problem with the CH1 output are twofold:
1. The CH1 output is about 3x more noisy (RMS) then the CH2 output.
2. The CH1 output is unable to regulate down to the minimum setting: when 1mV is selected, the output is 20mV (which agrees with the read back).
At first I speculated that problem #1 wasn't a problem, maybe it's just coupling of display or digital noise onto the output. But when combined with problem #2 I think it may imply there is a problem.
Any ideas on what to check first would be appreciated.
Thanks,
-tg