~60kHz oscillation on bench power supply output

[JohnnyMalaria]

I have a triple output bench power supply (HYelec HY3003-D) that has developed a problem on all outputs (inc. fixed 5V) in CV mode. There is an approx. 60kHz oscillation at least 0.2V in amplitude (0.6V at 15V output). The problem is not present in CC mode. It is present in independent, parallel and serial configurations. As the photos show, even with zero output the oscillation is still there. The file names indicate the voltage and mode.

Has anyone seen this fault before and, if so, were you able to make your own repair?

Thanks.

[Jwillis]

I swiped this from another post. The LM741's are the mode indicators I believe.Maybe one has gone funny .Does that 60khz appear on both master and slave .Does it appear on the 5 volt output as well?

[David Hess]

Make sure output capacitor C20 which is required for frequency compensation is not shot.

[JohnnyMalaria]

I swiped this from another post. The LM741's are the mode indicators I believe.Maybe one has gone funny .Does that 60khz appear on both master and slave .Does it appear on the 5 volt output as well?

Thanks. I've taken apart my unit. There are two identical PCBs labelled 2SD2163. The only difference I can see is that the slave has a yellow and a brown wire in the bundle connecting to the left side as shown in the attached image whereas the master board has jumper wires. The schematic you provide is a bit different. Does the dashed outline for the slave identicate that it is the same except for the specific components shown?

Contrary to what I said earlier, the oscillation is not on the 5V. It is always on the master in CV mode (irrespective of Independent/Serial/Parallel) even at zero output. It doesn't show on the slave in independent mode. In serial mode, it does show but at a difference frequency (80kHz vs 60kHz approx.) In parallel mode, the output of the slave is identical to the master. Note, the frequency for the master is always the same. I've also operated the unit without the slave board and see the same behaving with the master. So, it seems the fault lies with the master board.

I suppose an obvious next step is to operate in independent mode and probe around starting at the input from the main regulator board until I see a difference.

[JohnnyMalaria]

Make sure output capacitor C20 which is required for frequency compensation is not shot.

Thanks. I tested it for the master channel. The cap itself is on a small board for the front terminals. It appears okay out-of-circuit.