Power Supply Question

92VINCE · 01-23-2006, 01:21 AM

Hello,
I am working on a computer with dual Pentium II MMX processors, 128MB RAM, SCSI HDD, Ethernet card, FDD and Win95.
The other day I thought the 300W power supply went out, so I located another 300W power supply. I tried to replace it but the new power supply did not power up the computer either. I also tried to replace it with a Dell Dimension power supply which functions, but nothing again.
The interesting piece is that the new power supply does not power up the Dell Dimension either. It seems the Dell is an 85W. Am I crazy?
Any ideas?
Thank you.

-Vince

**Doby** · 01-23-2006, 08:16 PM

Hi,

Could you please explain what you mean by powerup, when you push the button is it dead or are there lights and fans?

If its dead it could be the case switch I can explain how to test for this, or it could be the psu witch we could also test for.

If there are lights or fans then thats a whole other ballgame.

Rick

92VINCE · 01-24-2006, 07:58 AM

Thank you for you reply.
When I push the power button no lights, no fans, no clicks, nothing.

-Vince

**Doby** · 01-24-2006, 05:47 PM

Remove the power supply from the case and plug into the wall outlet then on the 20 pin connector short the green and any black wirer with a paper clip, this should turn it on if not it is bad.

If the psu turns on then install it back into the computer.
If this is a dell psu the pin out maybe different on the 20 pin connector therfore this method won't work

Trace the wirers from the case switch back to were they connect on to the motherboard, take note to what pins they are attached and remove them.

Touch the to pins with a screw driver for a second or two then release, this should start the computer if not the case switch could be bad

92VINCE · 01-24-2006, 09:05 PM

Wow! That was very interesting. Both power supplies work when I shorted the green to the black wire.
Unfortunately the screwdriver test was not successful.

**Doby** · 01-25-2006, 06:21 PM

Try touching the 2 pins that the case switch connect to again this time try a different screw driver and hold it there a little longer with a slight rubbing motion, I am just being sure and grasping at straws but if both psu's turn on but the board will not power on with this method not even for a second the motherboard must be bad

ebackhus · 01-25-2006, 06:57 PM

Examine the capacitors and MOSFETS on the board around the power connector and CPU. If any capacitors are swollen or seem to be leaking then they've gone bad. Replacement is not easy and generally an acceptable reason to toss the board. If any MOSFETS are bad then that's another reason to replace it.

92VINCE · 01-27-2006, 12:11 AM

Thank you very much for your help. It was good advice to try the screwdriver again. This time I connected the correct pins with the screwdriver and it started the computer. I must have had the switch connector on the wrong pins. I learned a lot and appreciate your help.

-Vince

**Doby** · 01-27-2006, 09:03 PM

You are very welcome, I am glad you found the problem and pleased that you learned from your experiance here at TSF, thats what this is all about, be sure to stop back in and share your knowledge.

Rick

01-23-2006, 01:21 AM	#1 (permalink)
92VINCE Registered User Join Date: Oct 2004 Posts: 44 OS: Win98	Power Supply Question Hello, I am working on a computer with dual Pentium II MMX processors, 128MB RAM, SCSI HDD, Ethernet card, FDD and Win95. The other day I thought the 300W power supply went out, so I located another 300W power supply. I tried to replace it but the new power supply did not power up the computer either. I also tried to replace it with a Dell Dimension power supply which functions, but nothing again. The interesting piece is that the new power supply does not power up the Dell Dimension either. It seems the Dell is an 85W. Am I crazy? Any ideas? Thank you. -Vince

01-23-2006, 08:16 PM	#2 (permalink)
Doby Moderator Hardware Team Join Date: Jan 2006 Location: Central PA (USA) Posts: 8,094 OS: XP sp2/ Vista My System	Hi, Could you please explain what you mean by powerup, when you push the button is it dead or are there lights and fans? If its dead it could be the case switch I can explain how to test for this, or it could be the psu witch we could also test for. If there are lights or fans then thats a whole other ballgame. Rick __________________ Would you like to help TSF fight cancer and other diseases??? JOIN TEAM TSF

01-24-2006, 05:47 PM	#4 (permalink)
Doby Moderator Hardware Team Join Date: Jan 2006 Location: Central PA (USA) Posts: 8,094 OS: XP sp2/ Vista My System	Remove the power supply from the case and plug into the wall outlet then on the 20 pin connector short the green and any black wirer with a paper clip, this should turn it on if not it is bad. If the psu turns on then install it back into the computer. If this is a dell psu the pin out maybe different on the 20 pin connector therfore this method won't work Trace the wirers from the case switch back to were they connect on to the motherboard, take note to what pins they are attached and remove them. Touch the to pins with a screw driver for a second or two then release, this should start the computer if not the case switch could be bad __________________ Would you like to help TSF fight cancer and other diseases??? JOIN TEAM TSF

01-25-2006, 06:21 PM	#6 (permalink)
Doby Moderator Hardware Team Join Date: Jan 2006 Location: Central PA (USA) Posts: 8,094 OS: XP sp2/ Vista My System	Try touching the 2 pins that the case switch connect to again this time try a different screw driver and hold it there a little longer with a slight rubbing motion, I am just being sure and grasping at straws but if both psu's turn on but the board will not power on with this method not even for a second the motherboard must be bad __________________ Would you like to help TSF fight cancer and other diseases??? JOIN TEAM TSF

01-25-2006, 06:57 PM	#7 (permalink)
ebackhus Manager, Design Join Date: Apr 2005 Location: SATX Posts: 14,286 OS: WinXP Pro SP3/Windows 7 RTM My System Blog Entries: 28	Examine the capacitors and MOSFETS on the board around the power connector and CPU. If any capacitors are swollen or seem to be leaking then they've gone bad. Replacement is not easy and generally an acceptable reason to toss the board. If any MOSFETS are bad then that's another reason to replace it. __________________ ----------------------------- There are no dumb questions, unless a customer is asking them. Help in the fight against cancer and other serious illnesses.

01-24-2006, 07:58 AM	#3 (permalink)
92VINCE Registered User Join Date: Oct 2004 Posts: 44 OS: Win98	Thank you for you reply. When I push the power button no lights, no fans, no clicks, nothing. -Vince

01-24-2006, 09:05 PM	#5 (permalink)
92VINCE Registered User Join Date: Oct 2004 Posts: 44 OS: Win98	Wow! That was very interesting. Both power supplies work when I shorted the green to the black wire. Unfortunately the screwdriver test was not successful.

01-27-2006, 12:11 AM	#8 (permalink)
92VINCE Registered User Join Date: Oct 2004 Posts: 44 OS: Win98	That Did It Thank you very much for your help. It was good advice to try the screwdriver again. This time I connected the correct pins with the screwdriver and it started the computer. I must have had the switch connector on the wrong pins. I learned a lot and appreciate your help. -Vince

01-27-2006, 09:03 PM	#9 (permalink)
Doby Moderator Hardware Team Join Date: Jan 2006 Location: Central PA (USA) Posts: 8,094 OS: XP sp2/ Vista My System	You are very welcome, I am glad you found the problem and pleased that you learned from your experiance here at TSF, thats what this is all about, be sure to stop back in and share your knowledge. Rick __________________ Would you like to help TSF fight cancer and other diseases??? JOIN TEAM TSF