HP Z600 PSU Delta DPS-725AB Dead

[arrgh]

Hi all,
I have an HP Z600 Workstation that worked fine until somedays ago. Now, it won't power up and the green led on the PSU is not turning on.

Pulled out the PSU from the chassis and opened it. No visibile signs of burned ICs from what i see.
The model of the PSU is a Delta DPS-725AB, and the PCB is a DPS-725AP.
I've made some high res photos that are attached.
I've done some general testing and I found IC902, that is a TNY279PN, was shorted (I think): drain-source resistance was about 2-3 ohms.
I've a brand new TNY279PN at home so I tested it and the drain-source resistance was about 5.5Mohms. Thinking it was the problem, I replaced the IC on the PCB, but the PSU still not working.
I've replaced also the 100nF capacitor on the BP/M line but nothing changes.

Voltage on the main big caps is about 322V, I marked it on the photos.
Other reads over the TNY279PN:
EN/UV voltage: 1.89V
BP/M voltage: 1.80V (from the datasheet I've read that it should be over 5.85V, I'm right?)
Main cap positive-Drain: ~320V
Drain-Source voltage: 3.90V

I think this circuit with TNY is for 5Vsb but I'm not sure, can you confirm? If so, the D-S voltage should be ~5V
What can be the problem, and what could I test to find it with you?

Thanks all in advance

[stj]

check fuses and fuseable resistors,
and replace any cap less than 100uf related to the chip

[R_J]

I think this circuit with TNY is for 5Vsb but I'm not sure, can you confirm? If so, the D-S voltage should be ~5V

This ic is likely for the standby voltage but this is not how the ic operates, the internal mosfet switches the primary of the transformer, it is the transformer secondary winding, diode and cap that gives you the 5 volt standby. Download the datasheet and look at the sample schematic. You need to check the Drain voltage with respect to HOT GROUND (main bridge rectifier negative lead) The drain voltage should be close to 300 volts, the source voltage should be at hot ground. Check R901, it might be open

[arrgh]

Originally Posted by R_J

This ic is likely for the standby voltage but this is not how the ic operates, the internal mosfet switches the primary of the transformer, it is the transformer secondary winding, diode and cap that gives you the 5 volt standby. Download the datasheet and look at the sample schematic. You need to check the Drain voltage with respect to HOT GROUND (main bridge rectifier negative lead) The drain voltage should be close to 300 volts, the source voltage should be at hot ground. Check R901, it might be open

Thank you for these information R901 is as fusible resistor, right? On the top it's written 10ohm F1J... Desoldered it, and tested: totally open, not 10ohm.
The replacement that I found is a FRN01WK0100A10 by Royal Ohm, can be good? If not and I'm wrong, let me know.

Thank you

[R_J]

Yes, the resistor will work, but I will almost guarantee the ic is bad, I would also replace C905 & C907, since this is the standby circuit, it is on all the time and the caps can dry out over time (they could be ok but they are cheap to replace)

[arrgh]

Hi all,
Here's an update after replacement components arrived.

Components replaced as suggested:
IC902
R901
C905
C907

PSU is fully working now, tested under stress and with several on/off cycles. For now everything is ok!

Thanks for your precious advices and for your time

[R_J]

Thanks for the feedback, Glad to here it is working, long live the power supply

[[email protected]]

Hi!

I am new on BadCaps community.

I work on a research center in Brazil, and we have several HP Z600 workstation. Many of them are presenting failures on power supply model Delta DPS-725Ab.

So I will appreciate if someone could provide the schematic diagram of Delta DPS-725Ab power supply.

I thank you for helping.

Regards

Wilson Carvalho Jr

[Dlas]

Salutes, I have a similar problem with DPS 725AB, it starts with green led, a¿nd give voltage output for about 20 econds and then goes off totally, I am not sure what the standby cables are though (green and violet?), I someone can orientated me please

[PeteS in CA]

I see that this is not a P/S with a standard 20- or 24-pin ATX connector. However, if Delta followed ATX-style color coding inside the P/S, purple would be the 5V Standby.

Another question, server power supplies sometimes will run for several seconds and then shut down if the fan never ran. Does the fan run during the 20 seconds it has output voltage?