I repair an old APLAB ZD3203 DC Lab Power Supply that I rescued from the dumpster. It had 2 big issues, one with extremely dodgy pots and another with output transients when turning it off.
I have posted some high-resolution images of the teardown over at the EEVBLOG forum here: https://www.eevblog.com/forum/testgear/anybody-know-anything-about-this-signal-generator/ (As well as some additional tests)
Repeated here for convenience:
Top of the main board
Top of the screen board:
Bottom of the main board:
Some additional tests
(Suggested by 'Kleinstein' from EEVBlog forum):
1) Noise, e.g. from the SMPS or just from the DAC: So maybe use just a DC or low amplitude sine.
DC out at 1V, AC coupled, output OFF: Same as above, output ON:
2) DAC linearity: This can usually be seen from a slow triangle / ramp.
Triangle wave, 1KHz, 1Vpp:
3) Output amplifier slew rate: Many similar low cost generator run in to a slew rate limit with full amplitude and high frequency. So usually the maximum amplitude is reduces at the highers frequency.
Here's a sine wave, 25MHz, set to 1Vpp (but into a 50 Ohm load so what we 'should' see is 500mVpp)
Same as above, but a square wave:
4) There are 2 relays per output channel. So this could be an output attenuator. This has good sides, but might also limit the Offset range, when using low amplitudes.
Looks like you were right about the output attenuators, at 100mVpp setting (into 50 Ohms again), the maximum offset I can set is 0.25V;
I ran many many more tests, see results @ : https://www.eevblog.com/forum/testgear/anybody-know-anything-about-this-signal-generator/