PSU2 1.1 - fault when repurposing

[Pav]

Hi Tony, you find me on day 6 of catching covid (from my brother who came to visit!) trying to debug an Oakley issue. I am using a PA30 with psu2 issue 1.1 power supply to test an mfos 5U sequencer build. It has worked fine in its previous role , so i was surprised when on switching it on both fuses were blown. I refitted new fuses, and amber and green leds lit so i shrugged and put it down to mechanical knock, or cosmic rays.
but further testing with dmm reveals the +15v rail is giving +26.9v
the -15v rail is fine. The + adj trimmer had no influence on this weird value.
Any thoughts ?

cheers Pav

[Synthbuilder]

I'm sorry to hear you caught Covid. I hope your recovery goes well.

... but further testing with dmm reveals the +15v rail is giving +26.9v
the -15v rail is fine.

That sounds like a short between the input and output pins of the LM317 regulator. 27V would be the sort of voltage I would expect from the smoothed voltage that supplies the regulator. Putting D4 around the wrong way would also do this sort of thing.

[Pav]

Checked diode orientations were correct, replaced the voltage regulator
and it is fixed.

More than can be said of the mfos sequencer.
I seem to be frying 40106s but no evidence why as yet.

[collinspr]

Hi Pav,

Which of the 40106's is getting 'fried'?

Paul

[Pav]

Apologies for late reply ....I am ashamed to say I wired -15v to ground on one of three PCBs in mfos sequencer and fried most of chips - they were hot to the touch. I have replaced most chips to get it working, and will keep and test on a breadboard to see if any survived. I believe this would cause the PSU issue too.

[collinspr]

All part of the learning process

During build, at the first power up, it’s a good idea to apply power and check supplies at the power pins on IC sockets before inserting the chips.

At least you know what the problem was!

Paul