Bench PSU question

[Crystaleyes]

Giving the socket a quick clean and a close look, nothing jumps out at me.

One other thing, while I remember, is that when the voltage is set to zero, and then the amperage is also set to zero. the voltage goes up to around 5 -6 volts. Not sure if that might be a dodgy pot but a quick test of them shows that the voltage pot goes from 1K down to 1.8 ohms and the amperage pot goes from 10k down to just under 4 ohms.

[stj]

check the tracks from end to end in each pot

[redwire]

Where is the output capacitor? You need at least 10-100uF cap at the regulator's output for stability or it can oscillate. It might be doing that.

A weakness with this PSU design, and every bench PSU has shortcomings... is the for the output voltage to spike up when you shut off power. You can have it set to 5V and then turn it off or a mains failure happens, and the output voltage spikes up and blows whatever you were powering. It's because the 5V rail falls fast (powering LED panel meters) so the control op-amp can't operate but the pass transistor gets turned on full until the big caps discharge on the HV rail.

Another possible weakness is charging batteries I would guess 12V is the max. but a 24V battery could backfeed and blow parts if the PSU voltage was set low say a few volts, or power outage - and you connect the battery.
For reverse-polarity protection I just add a big MR756, 6A10 or 10A10 for good smoke and sparks whenever I do that by accident lol.

[Crystaleyes]

check the tracks from end to end in each pot

Think I'm just gonna put in some new ones. I have plenty here...

[Crystaleyes]

Where is the output capacitor? You need at least 10-100uF cap at the regulator's output for stability or it can oscillate. It might be doing that.

A weakness with this PSU design, and every bench PSU has shortcomings... is the for the output voltage to spike up when you shut off power. You can have it set to 5V and then turn it off or a mains failure happens, and the output voltage spikes up and blows whatever you were powering. It's because the 5V rail falls fast (powering LED panel meters) so the control op-amp can't operate but the pass transistor gets turned on full until the big caps discharge on the HV rail.

Another possible weakness is charging batteries I would guess 12V is the max. but a 24V battery could backfeed and blow parts if the PSU voltage was set low say a few volts, or power outage - and you connect the battery.
For reverse-polarity protection I just add a big MR756, 6A10 or 10A10 for good smoke and sparks whenever I do that by accident lol.

Thank you for the suggestions. I'll give that output capacitor a go and let you know how it goes. If that works and the voltage stabilises, then I'll give the diode a go too.

Nice one!