I have 2 of these supplies that are not working and have yet to resolve the problem. See the following for a "repair" of this power supply that may or may not resolve your particular problem.

Dan

Link:

 

I have 2 of these supplies that are not working and have yet to resolve the problem. See the following for a "repair" of this power supply that may or may not resolve your particular problem.

Dan

Link:

I went ahead and fed back 5v dc at low current into the 5.1v pin output. I guess this can check for pwm operation and feedback. I probed at pins 1&2 of the lm339n with my scope

 

I went ahead and fed back 5v dc at low current into the 5.1v pin output. I guess this can check for pwm operation and feedback. I probed at pins 1&2 of the lm339n with my scope

Sorry for the repeating multiple pictures I’m having trouble uploading them

 

I went back and tried testing the optocoupler and possibly fried it. Either in circuit or out of circuit https://forum.allaboutcircuits.com/threads/testing-optocoupler.176792/#post-1601509

I know I should have stopped at this point. I then put the Optocoupler back in and jumped its pins 1 and 2 to disable the safety shut down so I could check the pins at the green hybrid pwm board. I then powered the unit up. Now I’m I hearing a fizzling boiling sound, I got scared and thought it was a cap to about to explode and smelled something I then killed the power immediately and noticed the heat sink for the large power transistor near the bulk caps was getting warm only after few seconds of it being plugged in

Oh I forgot to mention I snipped off the jumpers and plugged it back in and am getting the same really scary sound!! Now I think I really ruined it!!!

It’s funny I didn’t at all notice this sound at all before could I have shorted something is there anyway I could continue safely I’m just trying to learn from my mistakes

Could I power it up at a lower input voltage like at 60v with the variac and still safely poke around??

 

Ok I went back and replaced the optocoupler. I went ahead and powered it up again for like 10 seconds then unplugged it. I quickly checked the large bulk caps with my meter to make sure no large voltage was still present in the large bulk caps. By just guessing I felt the heatsink for the large power transistor was somewhat warm even after only like ten seconds on and then turned off. Maybe the problem is in this area???

Oh I do hear the same chirping sound as well!!!

 

In posts #10 and #11 you make it clear that you are pretty much a beginner in these things. There's nothing wrong with that, BUT...

Switch-mode power supplies are NOT easy things to diagnose and work with. They have defeated many more experienced people (see Dan's post, #24) and can quickly and easily destroy expensive equipment (and even you!) if you don't know what you're doing. I would recommend looking for a replacement, either a direct replacement or a compatible.