CH1 on GPD-3303S is noisy, can't go down to 0V

[technogeeky]

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

[coromonadalix]

Maybe check the main voltages noise before and after the power mosfets, if its stay the same under no load,  checks for bad solders, bad contacts, connectors not fully inserted ??

You could compare the two channels analog to digital converters (DAC) inputs

Found this :
https://www.eevblog.com/forum/testgear/quick-look-gw-instek-gps-3303-power-supply/ 

and a verification adjustment manual :
https://www.eevblog.com/forum/testgear/quick-look-gw-instek-gps-3303-power-supply/?action=dlattach;attach=115779

[Shock]

Have you tried setting higher voltages, what noise do you see there? What happens with a resistive load?

[Mr. Scram]

Is yours actually this version with the gap or is it the newer one with all jacks equispaced?

[technogeeky]

Is yours actually this version with the gap or is it the newer one with all jacks equispaced?

It's the version with the gap, exactly as pictured.