Thanks for the PDF link, duak. That looks like an interesting read and should improve my understanding of these supplies. The ganging and remote control aspects make sense for the positive ground configuration.
Okay, so I made a silly mistake when I posted up those last scope captures--I had C20, the output filter cap, disconnected from the rear strapping points from prior debugging efforts. The presence of C20 doesn't seem to make a huge difference in CV mode, but it definitely affects CC operation (perhaps for the reasons xavier60 mentioned?). After installing C20, the output ripple went from ~6 mVpp to 660 µVpp
.
That being said, I have a few more questions. I know that some output ripple is expected, but I want to be sure I understand things:
First off, the 60 Hz sine wave in CV mode at TP 43 was a result of poor probing and close proximity to the input transformer
. However, when in CC mode, I could definitely trace the anomalous 60 Hz waveform from TP43 all the way to TP22. Again, I don't have the best probes for high-sensitivity measurements, but the averaging function on my scope got me close enough to where I could trigger on a waveform and be reasonably assured of a signal on those test points.
Out of curiosity, I compared the -4.3 V rail to the other references. It's definitely noisier and seems to correspond to the output ripple waveform. Even though the supply is working within its specifications now, could I assume that the output ripple is coming from the -4.3 V rail through Q3 and/or Q5? I would guess that some component of the waveform feeding the regulator (TP22) is also proportional to the sawtooth wave coming into the pass transistors, i.e. from CR26 and CR27.
Lastly, I have a question about probing VR4, the 4.3 V Zener diode. When I touched my scope ground lead to either side of VR4, the output of the supply went to zero, probably due to some kind of internal short. This seems strange to me, since I didn't have any other probes connected and the supply was essentially floating. I had to measure the -4.3 V by probing between TP41 and +S (not TP23). What would cause this? I didn't have any trouble probing directly across the 24 V, 53 V, and 62 V rails from the transformer.