I had a bench power supply finally act weird, which I only noticed when
playing with one of the UV LEDs, which even radio shacks sells now.

At one point, when in CC mode, the LED started to flicker and the power
supply made a weird clicking sound.

Outside of CC mode, the output looked OK. The B output (dual output unit)
worked fine.

The maker, TTI in the UK kindly supplied the service manual which I wanted
for the recalibration steps.

It turns out one of the internal -5v regulators (just a zener) for
powering the front control panel was completely missing. I had no idea it
belonged there as the board looked pretty clean with nice solder fillets
on the 3 pads where the sot-23 zener belonged. Super close inspection
showed there may have been glue/flux/something where the body of the diode
was.

I guess it never wetted correctly at the factory and then 5 years later
FINALLY fell off.

So the lesson is two fold

- check the power supplies inside broken power supplies
- maybe missing parts weren't options or ECs.

If anybody in the US has a spare BZX84C5V1 5.1V 350mW sot-23 zener they
can drop in an envelope, I'll send a few bucks your way. drop munge from
my email address.