Asus P2L97 dead due to failed power supply - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: July 27, 2016, 07:48:46 pm
content: Hey guys, I have an old Pentium II Asus P2L97 motherboard that was killed by a failed power supply. I believe that the power supply sent a spike along the 5v standby rail although I'm not certain. This was my first ever PC so it means quite a lot to me. When I plug a good power supply in, it immediately powers up and the fan spins. I can hold the power button for a few seconds and it will turn off. If I press the button again it will turn on. I get no beeps from the speaker and nothing on the screen. I am not sure if the graphics card is dead too but I am certain the board is because it always used to beep after it POSTed. I know my memory is good because I have tried it in another computer. I also replaced every electrolytic cap on the board just in case they had failed but that made no difference.If anyone has any ideas I would love to hear them. Thanks

author: Raff
author_rank: Regular Contributor
timestamp: July 28, 2016, 03:08:19 am
content: I usually start with a POST card similar to this onehttp://www.dx.com/p/pc-post-diagnostic-test-card-motherboard-analyzer-for-pci-4-digits-red-420029#.V5l2bmYkqUkBetter still if you can find one with external LED board as its often hard to see them if its inside a computer case.You will then be able to tell if the CPU is getting clock and the BIOS is being accessed by the CPU at least.I mostly use mine to help find shorted RAM as often the motherboard wont even beep or display anything with shorted RAM especially if it has on board video support.Good luck.Raff.

author: Stefan Payne
author_rank: Contributor
timestamp: July 28, 2016, 03:20:54 am
content: 1. What kind of Power Supply did you use? Can you post a picture of the unit?2. How did it fail? Was the +5VSB rail still in spec and not like 12V or something like that?3. What Power Supply do you use now?There were some changes to the spec that can make newer, good PSUs to not work with oldish hardware -> Does your board need the -5V rail? Newer units only have a -12V rail.

author: canadaboy25
author_rank: Regular Contributor
timestamp: July 28, 2016, 04:27:43 am
content: Quote from: Raff on July 28, 2016, 03:08:19 amThanks I was thinking of doing this so I'll order one and report back once it's here.Quote from: Stefan Payne on July 28, 2016, 03:20:54 amI'm afraid that power supply was scavenged for parts long ago. I still have the remains but I don't think that will do much for seeing what voltage it put out. I'm pretty sure I was getting absolutely nothing out of it after it blew but I'm not sure. I've posted pictues of the label and burnt portion of the power supply.I posted a pic of the power supply I'm using now. I know my board needs -5 volts because that voltage was for the ISA slots which I have and use for my sound card. The new power supply also has a -5 volt white wire.It sucks that I don't know the actual fault. Maybe I can follow the traces on the power supply to see which line got burnt if need be.

author: Stefan Payne
author_rank: Contributor
timestamp: July 28, 2016, 04:47:41 am
content: Well, the good news is that it's a more or less decent quality PSU, at least it should be (CWT is around today and still make more or less good PSUs though their soldering isn't that good)The bad news is that it looks like the PSU is rather old and uses the so called 2 transistor standby thingy. That means that if the right capacitor (one of the smaller ones) goes bad the +5VSB rail goes way out of spec and fries something connected to it.So with this knowledge it's possible that everything connected to this rail is fried - like chipset and memory...

author: Rasz
author_rank: Super Contributor
timestamp: July 28, 2016, 07:03:40 am
content: take everything off the board and trace what is connected to standby rail, probably some linear reg

author: Ijaz
author_rank: Contributor
timestamp: July 28, 2016, 07:18:08 am
content: Quote from: Raff on July 28, 2016, 03:08:19 amDidn't know any such thing exists, thank you for introduction.

author: Stefan Payne
author_rank: Contributor
timestamp: July 28, 2016, 12:56:20 pm
content: Well, yeah, I think there are also such things for PCI express and some higher end boards (like the MSI A88X-G45 Gaming, wich was the most expansive FM2+ Board at the time for about 100€) also have such things onboard...

author: canadaboy25
author_rank: Regular Contributor
timestamp: July 28, 2016, 05:13:50 pm
content: Quote from: Stefan Payne on July 28, 2016, 04:47:41 amHow could the memory be fried if it works in another PC? If the chipset is fried putting a new one on the board wouldn't be too bad.Quote from: Rasz on July 28, 2016, 07:03:40 amWhen you say take everything off, you mean desolder every single component?Quote from: Stefan Payne on July 28, 2016, 12:56:20 pmYep that's exactly right. I have an old MSI motherboard and it has a external readout that fits into an unused PCI slot on the case and has 4 LED's which read out any faults.