No voltage on the source pins of PNY280pn switcher

[eagle1109]

Hi,

I started working on this Dell PSU after purchasing a new 220V/100W current limiter lamp.

My start inspection is that the PNY280pn has 385V on Drain pin but 0V on source side. Why it's not working ?

 

[eagle1109]

Try to look for dry points in the board and resolder, maybe bad contact cause the psu not stable

I didn't know what you mean by dry points, maybe you mean bad soldered points that are loose or cracked out. But the soldered point on this PCB are ok.

also connect the psu with current limiter lamp you have and see if it will shut down or no

Yep that what I do all the time no way I would connect any PSU that is targeted for repair without the protection lamp.

For the -12 v reading I think normal

Yep, you're right it's the same voltage level on the working one.


Here's a video for my last update on this PSU.

 

[betwixt]

On most of these PSUs there is no regulation on the +12V or -12V lines, because they are not usually critical and because the voltage tracks the 5V and/or 3.3V lines it is assumed to be correct if they are.

If the PSU is unstable, try it with a load attached. I keep an old car headlamp bulb for this purpose. Although rated for 12V, it will still draw a few amps from the 5V line and it will glow dimly so you can see voltage is present. Often these PSUs require some load or they tend to go over-voltage and then the feedback loop tries to drop the voltage but the output capacitors hold it up. The result is a fluctuating voltage, never far from correct but almost randomly rising and falling a little.

Brian.

 

[Gaber Mohamed Boraey]

What is the missing voltage with you now?

 

[eagle1109]

No missing voltage. It's working perfectly.

One good thing that helped me is having another working identical PSU to compre it for measurements.

I have other faulty ones but different models. Now if I can't repair them easily then I better find a working one which will help a lot.

 

[Gaber Mohamed Boraey]

No missing voltage. It's working perfectly.

Okay, and how you solved this one problem?, or was no problems ?

 

[eagle1109]

I explained it in the video.

After replacing the switcher, I forgot to short the boot pin then I realized it and then I shorted the boot pin and it worked.

Another strange thing is that the 12V was missing for some time then it got present.

Anyway I will put this PSU in a rig and check if it will work under load and how much it will last.