T3620 Power Supply Failure

Question

Hi All,

My Precision Tower 3620 was humming along yesterday and the then all of sudden it wasn't. It no longer does anything in response to the front-panel power switch. If I push the little black momentary switch at the back of the power supplier, the green LED lights up and stays lit as long as I hold the momentary switch closed. The green LED goes out as soon as I release the momentary switch.

The power supply is a model HU365EM-00 (Dell P/N 7VK45). The "UP/N" is HK465-11PP.

I disconnected the power supply from the computer and tested the various outputs using a paperclip to hold closed the momentary switch on the back of the PSU. With the momentary switch closed I get the following voltages at the three PSU output connectors (relative to black wires/PSU chassis):

P1 White wires: +12.25V

P1 Purple wire: +11.54V

P1 Gray wire: +4.85V

P2 Yellow wires: +12.25V

P3 Brown wires: +12.25V

I have not tested the power supply with it connected to its respective loads (i.e. the motherboard).

If the problem turns out to be the power supply, it appears to be "in-stock" at several outlets (including a few Ebay sellers), but these suppliers who carry it look a bit dodgy. This makes me think that I am foolish not to keep a spare PSU on-hand for just such emergencies. Of course, that assumes the problem is in the PSU.

I don't have a good understanding of how the momentary switch on the front-panel of the computer interacts with the PSU to "latch" the on state. Nor do I know if the momentary switch on the back of the PSU is supposed to latch the on-state in a similar manner to the way the computer's front-panel switch latches the on-state.

Since the front-panel momentary switch connects to the motherboard and not directly to the PSU. I am thinking that there is some circuitry on the motherboard that plays a part in the PSU on-state latching process, but I am hoping that the problem is confined to the PSU as I don't relish the thought of having to replace the motherboard.

Any helpful suggestions would be appreciated.

Thanks!

speedstep · Answer

@Lima_One_Delta

Please press the blue Accept as Solution button below if the post answers your question.

Your built in self test says the power supply may not be the issue.

Disconnect all storage and replace the CMOS battery and see if it comes on or not.

Replacement power supply does not have to be DELL it can be a standard EPS12v unit that has 150W combined output or more on the 3.3v/5v rails.

I recommend the EVGA 700BR. You will also need a 15 pin sata power to 6 pin sata power cable if you have optional Optical Drive.

CRJ 15 PIN TO 6 PIN optical power cable

EVGA pn# 100-BR-0700-K1

EVGA-100-BR-0700-K1

InstantYo · Answer

I have the same problem with a T3620 at work. The green LED goes out as soon as I release the momentary switch. I can't run diagnostics because of that. I also assume it's a bad Power Supply.

Lima_One_Delta · Answer

Speedstep,

Thank you for your detailed reply

I replaced the CMOS battery (CR2032) and tried powering up with the power to all the external drives disconnected. That didn't seem to do anything. I didn't, however, disconnect the data cables from the external drives when I disconnected power. Not sure if that would make any difference.

It looks like the the +11.5V (purple wire on P1) comes up as soon as I plug-in the PSU (i.e. it's present even when the self-test button isn't pressed.The other voltages come up when I press the PSU self-test button.

I found a ~2.8V signal on the motherboard right next to the connector that goes to the front-panel power switch. It looks like there is a pull-down resistor at that point. The signal goes low when I press the front-panel power switch, but nothing happens in response.

The other thing I noticed is that the CPU fan spins briefly when I push the self-test button on the PSU, but it stops almost immediately. It is as if the CPU fan gets a pulse of supply voltage and then it gets cut off right away. Not sure what is up with that. In contrast, the fan on the video card turns-on and stays on when I press and hold the self-test button on the PSU

Is there any way to get schematics for the motherboard? Even if it were just the basic functions like the interface circuitry for the front-panel power-on switch, it would help. I get the feeling there might be some self-protection circuit that think there is a fault somewhere and is preventing the computer from booting up. I am out of my depth, however, as my experience troubleshooting PC hardware is almost nil.

Regards,

Mike.......

Lima_One_Delta · Answer

InstantYo, In case it is the power supply, I ordered a replacement. Hopefully I will have it here in a day or two. I'll advise on whether or not it fixes the problem. Regards, Mike...........

InstantYo · Answer

FYI: Something I noticed when I was messing with my T3620 and TPM module. I tried clearing the CMOS settings using the jumpers on the motherboard. Basically you take the jumper off the PSWD posts and put it on the CMCLR posts for 5 seconds. I found that if I left the jumper on CMCLR, my system acted like the bad power supply issue. Next time I get a chance to troubleshoot my bad unit, I'm going to mess with the jumpers.

Golfhat · Answer

Hello Mike, did you manage to resolve the issue as similar problem here, thanks

Precision Fixed Workstations

T3620 Power Supply Failure

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