Dell Studio 540 -- Dead, not power supply

I have a Dell Studio 540 desktop running Windows 7. Recently, the entire system shut down while I was using it. I had replaced the power supply once before so I thought that was the cause. However, I bought a replacement power supply (Diablotek) which was identical to the first power supply, but after that was installed, it was still dead. No led lighting up on the motherboard, no HD's spinning up, nothing. I replaced the power cord with one I know to work on another system, and still nothing.

I looked at the capacitors on the motherboard and none were bulging / needed replacement. That's about as far as my diagnostic skills go.

Is this indicative of the motherboard being "dead"? Is there anything else I can try? Any advice or guesses is sincerely appreciated.

Thos.

something is shorting then.

trying unplugging the molex power connector (white 4-pin) from any cd/dvd drive and powering on.

try resetting the CMOS by removing the jumper from the the 2 pins its on, pin 1 and 2 to pins 2 and 3 for a couple of second sand then back on pins 1 and 2 and powering on.

you could even try unplugging the molex power connector from the HDD to see if there is any life from the MB.

Quote from Thos19 : I have a Dell Studio 540 desktop running Windows 7. Recently, the entire system shut down while I was using it. I had replaced the power supply once before so I thought that was the cause. However, I bought a replacement power supply (Diablotek) which was identical to the first power supply, but after that was installed, it was still dead. No led lighting up on the motherboard, no HD's spinning up, nothing. I replaced the power cord with one I know to work on another system, and still nothing. I looked at the capacitors on the motherboard and none were bulging / needed replacement. That's about as far as my diagnostic skills go. Is this indicative of the motherboard being "dead"? Is there anything else I can try? Any advice or guesses is sincerely appreciated. Thos.

It certainly is an indication of a blown mobo. If you are 100% positive that the PSU is good, then it's pretty much a done deal.
If you can test your PSU in another machine or use a PSU from a functional machine, then you'll 100% sure that it is the mobo.

Quote from ReverseHandedJO : something is shorting then. trying unplugging the molex power connector (white 4-pin) from any cd/dvd drive and powering on. try resetting the CMOS by removing the jumper from the the 2 pins its on, pin 1 and 2 to pins 2 and 3 for a couple of second sand then back on pins 1 and 2 and powering on. you could even try unplugging the molex power connector from the HDD to see if there is any life from the MB.

I considered those possibilities, but the OP's machine just shut down while using it, as opposed to a machine that just won't turn on, so that rules out the shorting out or the bios factor, IMO.

Quote from RockySosua : I considered those possibilities, but the OP's machine just shut down while using it, as opposed to a machine that just won't turn on, so that rules out the shorting out or the bios factor, IMO.

mkay.

you need to unplug the hard drive floppy cd rom pull the memory after resetting the bios and see if it beeps


it is possible the power supply you got is not the right one too, I am not sure about your model but Dell and HP used to make their power supply proprietary by swapping 2 of the power supply cable pins

Quote from Thos19 : I bought a replacement power supply (Diablotek) which was identical to the first power supply,

Do you mean the power supply had been replaced previously? Because a Diablotek PSU is not identical to anything found in an original Dell, and JonnyGuru.com found that a 1050W Diablotek failed with a load of less than 600W [jonnyguru.com]. Dell factory PSUs are high quality.

I don't know how many LEDs are on your Dell motherboard, but one of them should light up whenever the PSU is providing +5V standby power from its purple wire (different from the +5V from the red wires), and that LED is wired almost directly to that wire, with nothing but a resistor and fuse between them. So if that LED doesn't shine, then:

1) the new PSU is bad. If you can't test it with another computer, as RockySosua suggested, do a rough test by using a bent paperclip to short its green wire on the big connector to either black wire next to it. The fan should then spin, but that doesn't mean the PSU is 100% good because it could still have a dead voltage rail or a weak one.

2) the motherboard blew an onboard fuse because a voltage surge caused a protective diode or chip to short. However I don't think most motherboards have such protective diodes, unlike hard disk drives.

3) a chip powered by the +5V from the purple wire was damaged and is shorting that +5V, causing it to shut down due to excessive current.

I think Dell has always used good brand capacitors that have a very good chance of lasting at least 5 years, even with power-hungry CPUs, except for a bad run of caps in 2001-2004 and maybe United/Nippon Chemicon models KZG and KZJ (brown plastic sleeving, 3 pie slices on top in the aluminum), which are still found in many motherboards. Not all bad caps bulge or leak. And while I'm not sure, I don't think bad caps will prevent the LED from glowing.

Quote from larrymoencurly : Do you mean the power supply had been replaced previously? Because a Diablotek PSU is not identical to anything found in an original Dell, and JonnyGuru.com found that a 1050W Diablotek failed with a load of less than 600W [jonnyguru.com]. Dell factory PSUs are high quality. I don't know how many LEDs are on your Dell motherboard, but one of them should light up whenever the PSU is providing +5V standby power from its purple wire (different from the +5V from the red wires), and that LED is wired almost directly to that wire, with nothing but a resistor and fuse between them. So if that LED doesn't shine, then: 1) the new PSU is bad. If you can't test it with another computer, as RockySosua suggested, do a rough test by using a bent paperclip to short its green wire on the big connector to either black wire next to it. The fan should then spin, but that doesn't mean the PSU is 100% good because it could still have a dead voltage rail or a weak one. 2) the motherboard blew an onboard fuse because a voltage surge caused a protective diode or chip to short. However I don't think most motherboards have such protective diodes, unlike hard disk drives. 3) a chip powered by the +5V from the purple wire was damaged and is shorting that +5V, causing it to shut down due to excessive current. I think Dell has always used good brand capacitors that have a very good chance of lasting at least 5 years, even with power-hungry CPUs, except for a bad run of caps in 2001-2004 and maybe United/Nippon Chemicon models KZG and KZJ (brown plastic sleeving, 3 pie slices on top in the aluminum), which are still found in many motherboards. Not all bad caps bulge or leak. And while I'm not sure, I don't think bad caps will prevent the LED from glowing.

Really? I had never heard of issues with the brand. I originally replaced the stock 250w PSU when it failed, as the 400w Disblotek was recommended specifically for the 540, over at the Dell Community Forums. When my 540 shut down, I thought the PSU was failing, I contacted Diablotek, and they offered to do a warranty swap. Of course the net result was the same.

Found a refurb motherboard on eBay for $95. We'll see what happens...

Thanks for all of the input, guys !

Thos.

Quote from Thos19 : Really? I had never heard of issues with the brand. I originally replaced the stock 250w PSU when it failed, as the 400w Disblotek was recommended specifically for the 540, over at the Dell Community Forums. When my 540 shut down, I thought the PSU was failing, I contacted Diablotek, and they offered to do a warranty swap. Of course the net result was the same. Found a refurb motherboard on eBay for $95. We'll see what happens... Thanks for all of the input, guys ! Thos.

FWIW, I have found Diablotek PSU's to be quite unreliable and NOT long lasting.

Well the replacement didn't cost me anything. If and when it fails, do recommend a particular substitute?

Thos.