problem with Delta GPS750AB A PSU. No +5v VSB

[smile]

Hello, I have problem with Delta GPS-750AB A PSU.
I checked almost all components on the PCB, desoldered and measured them.
The power transistors were desoldered tested with transistor tester.

All capacitors tested.
All diodes tested.

SMD transistors not tested.

The IC was blown TNY280PN, replaced
Also the resistor was blown is the blue one red arrow

on +5VSB I measure 0.9-1.9V jumping

What else to try?

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Here are more photos

[sam_sam_sam]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

You need to check the circuit for the standby for shorts you will probably have to do this the hard way unless you can find a circuit diagram for this board but I would replace every capacitor on the standby circuit for good measure and so you know that this is not the issue and start there

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

You need to check the circuit for the standby for shorts you will probably have to do this the hard way unless you can find a circuit diagram for this board but I would replace every capacitor on the standby circuit for good measure and so you know that this is not the issue and start there

Thank you for reply, I desoldered all electrolytic caps, tested them they are all OK. ESR is normal.
I even unsoldered transformers tested for shorts, normal.
I could not find any shorted diodes. The normal trough hole resistors all tested.

[CapLeaker]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

With a bad diode you wouldn’t be able to get that fluctuating VSB. Probably something else in that circuit either loading it down or it can’t regulate for some reason. Maybe something is open?

[R_J]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

There is a small electrolytic cap (C901) what is the DC voltage across it?

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

There is a small electrolytic cap (C901) what is the DC voltage across it?

This capacitor?

[R_J]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

This capacitor?

Yes, that one

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Thank you for your help.
Here is video file, the voltage jumps also all over the place. What to test next?

[R_J]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

If that is the voltage ACROSS C901, I would start by replacing it.

[CapLeaker]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Only because a capacitor looks good, doesn’t mean it actually is good.

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

The capacitor is good, as I said I desoldered and tested all capacitors on this PSU. Here I done it again just to prove a point.

2 different testers show good capacitor.

Why the voltage is jumping? What to test next?

[CapLeaker]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

I think 5VSB is the purple wire, the green one is PSon. Trace them and see if they are going to a supervisor IC like a Weltrend 7525 or something.
Usually the TNY2whatever produces the 5VSB, goes through a transformer, a diode, a filter cap, an inductor, followed by another filter cap, ending at a supervisor IC. Maybe the supervisor IC draws too much. Take it out and see what happens. Maybe take the inductor out and check op the voltage on the first cap. Basically you have to isolate and check things in sections. Eliminate a section at a time until you found your problem.

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Well the trough hole components were all removed tested then soldered back, I doubt I can find anything there. I wondered maybe somebody from experience knows what to test on SMD side as removing those is hard and you easily damage the only component

[CapLeaker]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

The supervisor ic consumes power all the time, because from it comes PSon. So take that IC out and see if that 5VSB voltage stabilizes.

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

I have connected +5V from my lab power supply to the +5VSB purple wire, the voltage got to stable +5V current drawn was 6mA !!!
There was no change with the PSU, I tried to start it with green+black wire and it did not do anything. I have replaced the standby optocoupler to another one still no change. Voltage unstable on +5VSB

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

The supervisor ic consumes power all the time, because from it comes PSon. So take that IC out and see if that 5VSB voltage stabilizes.

Well I removed the supervisor IC Dwa108-A with it's small PCB still same situation with unstable +5VSB.

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

So far I have replaced the TNY280PN,

LM393P, ICE1PCS02 both replaced on small board on primary side near TNY280PN.
You can see them on 1st photo.

There is still one IC uc3845b on same board unreplaced. Can this cause +5VSB to be unstable?

[smile]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Searching for TNY280PN unstable +5 vsb give only one result with same problem but no fix
https://www.powerint.cn/community/fo...y-standby-5vdc

[CapLeaker]

Re: problem with Delta GPS750AB A PSU. No +5v VSB

Searching for TNY280PN unstable +5 vsb give only one result with same problem but no fix
https://www.powerint.cn/community/fo...y-standby-5vdc

In this case the p6ke160 is short. it should not conduct both ways!