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HP DC7600 Fails to start

By sidepage-techrepublic ·
My HP DC7600 does not start.

Normall when I turn on the power supply switch, it would wait for me to press the power button. But now, as soon as I switch on power on the main supply, the power LED stars to blink in green continually (about each second, 1Hz cycle) and it never stops. Devices that connected to the PC and that have some LEDS also blink like wise. THERE ARE NO BEEPS.

I have read the manuals and troubleshooting guides from HP such as this one
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00368814/c00368814.pdf

but in vain. They all discribe failure cases in which the power LED blinks in red to give a hint on the problem. And these blinks are not continuous; they will come in packs of 2 to 10 in a cycle, cycles separated by a 2 second pause.

The only case described in the manuals of green power led being on are
1. Continuously on ==> Normal operation
2. Blinks in at 0.5Hz (once in 2 seconds) ==> in susended mode

I couldnt see the case in which the green power LED blinks continuously at 1Hz.

I tried a few tricks.

If I unplug CPU power cable from the main board, it behaves correctly; power LED blinks in red with the appropriate cylces to indicate that power supply is the problem.

I unseat the CPU, it again blinks the correct code in red, and beeps accordingly, to indicate that the CPU has been unseated. So it might not be a CPU problem.

I tried to unplug all devices, including RAM modules and hard drives, but in vain. GREEN LED blink continuously about once a second.

I have tried to reset CMOS; no change at all.

Does anyone have an idea of what the problem might be or what I should do?

Should I consider the mother board dead?

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All Answers

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Well replacing the Power Supply with a Know Good One

by OH Smeg In reply to HP DC7600 Fails to start

Is always the starting point. Unfortunately when these crappy PS die they can quite often damage the M'Board, CPU, RAM and so on so you need to test things.

But you always start by unplugging the PS and plugging in a Known Good one that you test with. This doesn't need to be mounted in the case or even have anything but the M'Board & Video Card if required connoted. If the unit will post with a Known Good PS you can then connect up the rest and see if it will boot or if it will not you will have to have a play with it to try to work out why this is so.

Also try changing the BIOS Battery these when flat can cause all sorts of problems.

Col

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Could

I agree with you. I probably needed to order a new power supply unit. But a few things kind of made me ruled out the PS.

The HP DC7600 has coded diagnostic LEDS that blink in certain pattern to indicate specific problem (accompanied by beeps of similar patterns). And there is actually a pattern to indicate power supply failure (Power LED blinks in RED 4 times @ 1Hz, the cycle repeats after 2 seconds pause). So i just think if it was a PS problem, either there would be no activity at all, or the diagnostic LEDS would indicate it.

FYI, the diagnostic LEDS has a number of very useful patterns of blinking (with beeps) to indicate pre-boot problems such as CPU not being installed, power supply failure, memory error, video error, PCA failure and wrong PS input voltage. The Power LED would blink in RED in some specific pattern.

But the pattern I was getting yesterday (Power LED blinking in GREEN @1Hz, continuously) is not even in the docs. And all error condition pattern use the red LED light not green.

Anyways, I gave up yesterday and went to sleep.

I woke up this morning, powered it up, and voila! It starts, and I am even able to write this post from it. As if nothing happened.

Any idea what might have happened here?

I'll go ahead and replace the battery just in case. at the moment that seems a more plausible culprit.

Thanks Col.

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Well at a guess

by OH Smeg In reply to Could

I would say the PS is working at reduced capacity meaning that the output voltage is correct but the Wattage is not right or Low. This can not be checked by the HP Flashing LED's.

Actually it's quite a common problem and if you ever get a computer that when you attach a Monitor to it claims that the Monitor isn't connected it's the PS.

I saw one like this today the owner had replaced the M'Board, CPU, RAM, HDD's, Optical Drives, Video Card, Video Capture Card and so on actually everything but the Case was replaced to save the cost of bringing it to a Tech for repair. Quad Core computers tend to be more expensive than a Power Supply and Labor from my prospective but this person now only needs to buy another case and he's got a backup computer for very little.

And he still had to pay me to fix it up. But what made it worse is that it's still Under Guarantee so I'm returning the PS to be replaced and giving that to him when it arrives.

Col

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Well, it came back ...

by sidepage-techrepublic In reply to Well at a guess

That makes a lot of sense. I'll try getting another PS to test it with.

But the news is, after working perfectly yesterday, I powered it off at arround mid-night and went to sleep. Woke up in the morning, tried to power it up, and you guess right, it does not start. Just as the day before yesterday, the green led flashes, CPU and chasis fun revolve at low speed. Everthing is silent apart from clicks from the speaker and flashes from the optical mouse all in sync.

I am just wondering, is there a logical explanation for the power supply not to work for the whole day (the day before yesterday), then worked yesterday for the whole day, and today it does not work?

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Well this is a Computer you can not expect :Logic to Apply

by OH Smeg In reply to Well, it came back ...

But it has to do with the Drain or Load placed on the PS at startup. While the unit is running the system draws very little current but attempting to start things when there is a High Load on thing they can fall over. Of course with Low Current available that also means that any motor in the thing like Fan's HDD Motors are not running correctly and will be under stress and have a shorter life.

Also if there is a spike of sufficient aptitude it could damage the system internals and this wouldn't normally happen if you had a Good PS. So the more you use it the shorter the other parts will last.

Col

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Some Tests ...

I managed to get access to another similar working PC at my old employer's office (nice of them, no?).

Before leaving home, I tried powering my system board and it would not start as usual.

So I took my PS and system board to my old mployer's office.

I started by puting my PS into the working PC and it powered up with no problem. So I thought my PS may not have a problem.

Next, I powered my system board using my PS, and it started. I expected it to fail because same setup failed at home a few hours ago, but it didn't want to fail! Damn! It powers up fine, as if nothing happened before (except the CMOS I had cleared).

Talking about high load, when it fails, I also try to power the system board with nothing but CPU and CPU fan. Could that cause that much a load to a 365W (max) PS?

Also this same PS has powered a machine here with all the other power consuming gadgets attached.

Now I dont really know what to test next.

I begin to suspect power from the mains at my place. Is this reasonable calprit?

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Well it could be a Marginal Mains Issue I suppose

by OH Smeg In reply to Some Tests ...

But if that was the case I would expect other things to play up as well not just a computer.

What's the TV look like? If it is not going all the way to the Top & Bottom of the screen it may be a Power Issue or if Electric Pot Plates are not working properly or constantly failing that could the problem But if it's only the computer acting up I wouldn't think so.

As for this particular Power Supply it needs top be tested over a period of time as you have already had it power up correctly one day and not the next. The only real way to test things from here is with a Known Good Power Supply and try it over a period of days. B

But saying that I've seen new 1000 W Antec Server Power Supplies not work out of the box properly. They will run Fans but not allow the system to actually boot. Another PS of the same Make & Model and the system works perfectly. As to what is happening inside it there is anything possible but I would be looking at the Chopping Transistors being the primary culprit. These depending on their maker can self regenerate partly over time and can work today and not tomorrow. But if you leave the computer running it will appear that they is nothing wrong with the system.

It's your call but a PS is the cheapest & easiest thing to replace to test things with I believe that buying a new M'Board to see if the PS is damaged is a tad expensive to test that way when you end up having to buy another Power Supply anyway and end up with a M'Board that is not required.

Col

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I should have listened ...

Well, I should have listened to you ;-)

The power supply is the problem.

I managed to borrow a working power supply for the weekend and it was working with no problem. The problem only recurrs when I plug mine in.

Fortunately the faulty power supply didnt managed to do much damage. Only that I noticed clock times were messed up, running slowly or going back for even on hour sometimes. I used HP diagnostic software and it indicated that the Real time clock was failing to update CMOS properly. I cleared the CMOS and tested again, it passed the test. So it seems that all is well ...

Thanks.

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While you are at it

by OH Smeg In reply to I should have listened .. ...

It wouldn't hurt to check the voltage of the BIOS Battery. When they get low they can do some really strange things and while not the problem now for the few $ spent on a new battery it will save you a lot of messing around.

Col

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