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New PSU won't POST; old PSU works

This is a discussion on New PSU won't POST; old PSU works within the RAM and Power Supply Support forums, part of the Tech Support Forum category. I'm trying to upgrade a 250W Bestec PSU with OCZ 600W SXS. The motherboard takes 20-pin without -5V pin. Bestec


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Old 01-25-2011, 01:41 PM   #1
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I'm trying to upgrade a 250W Bestec PSU with OCZ 600W SXS. The motherboard takes 20-pin without -5V pin. Bestec PSU has no -5V pin, and the system runs fine. I put in OCZ PSU, and fans (CPU, PSU and case) run, there is power to CD-ROM and hard drive, but motherboard won't POST -- no video signal according to monitor. I put Bestec PSU back in, and system runs fine. I put OCZ PSU back in, and no POST, no beeps, nothing. A week ago, I tried updating with a 400W Inland PSU with the same results. I concluded that the new Inland PSU was DOA. Now having the same experience with a new OCZ PSU, I'm doubtful that both brand new PSU's were DOA. What could be keeping this system from working with a new PSU besides faulty PSU's?

Compaq Presario 061 DQ181A-ABA S6500NX
Board: ASUSTek Computer INC. Kamet2 2.01
Bus Clock: 166 megahertz
BIOS: Phoenix Technologies, LTD 3.08 02/04/2004
2.15 gigahertz AMD Athlon XP
Windows XP Home Edition Service Pack 2 (build 2600)
SAMSUNG SP1604N [Hard drive] (160.04 GB)
PSU: Bestec 250W
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Old 01-25-2011, 05:39 PM   #2
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did you compare the main motherboard connector of the bestec to the OCZ are they colored coded wires in matching locations?


some OEM system manufacturers use proprietary power supplies which are wired differently than standard atx power units ..............dell was very handy at this and older compaq machines too
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Old 01-25-2011, 08:07 PM   #3
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linderman,

Thanks, nice thought, but no luck. Wires are color coded the same, and manual for OCZ PSU matches voltages for Kamet2 (aka ASUS A7V8X-LA) motherboard. I did put a voltmeter on the OCZ PSU and it showed the 3.3 connections had 3.5 V with no load and 3.4 V when connected to motherboard -- as read through the extra four pins that are not required for motherboard connection. My voltmeter may be innacurate, but there was likely a 0.1 V drop when connected to computer. Would that make any difference? Any other ideas?
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Old 01-26-2011, 01:29 PM   #4
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I have seen your problem on isolated cases with OEM systems; the problem is the new psu is not getting the signal it needs to start

you could try connecting the new psu to the motherboard (see bench build test) and then jump the motherboard case switch for a brief second with a paper clip; if no go
https://www.techsupportforum.com/foru...em-171424.html

then try jumping the green wire at the backside of the 20 pin main connector with any black wire in the 20 pin main connector / using a paper clip; there is no juice here so no need to worry about shock or anything like that; the green wire is a signal wire and the black is ground; you can try the same test for your own comfort as shown here
https://www.techsupportforum.com/foru...er-151526.html

(see testing DC voltages section) the green wire is #14 in the main connector

video how to here

YouTube - How to jump start your power supply unit!

when trying to start the motherboard connected you will need to touch the green wire and the black wire from the BACK SIDE of the connector as the front side will be hidden by the motherboard socket connection.
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Old 01-26-2011, 09:28 PM   #5
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linderman,

Using the case switch with the new PSU, all the fans work, and I can read 5V and 12V with a DVM on molex connectors. There is power to the CD-ROM because the drawer opens and closes. But there is nothing showing on the monitor, no POST, no beeps. I think this means the PSU got the signal to start. I also removed all the drives and got the same result. The only thing I changed is the PSU. Either PSU will make all the fans go, but the new PSU won't POST. If you think it would help, I could try to start the system using the new PSU and jumping the motherboard or the green wire, but it seems that the new PSU has started, but for some reason the motherboard, CPU, or memory is unhappy with it.
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Old 01-27-2011, 05:16 AM   #6
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your troubleshooting is spot on! the PSU is getting the signal to start for sure but for some reason the board is not compatible with new atx power suppies; like I was saying I have struggled with this personally myself once in the past and ended up replacing the motherboard as the customer wanted a new high end video card and the 300 watt bestec would not support it
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Old 01-27-2011, 05:31 AM   #7
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Asus A7V8X-X Socket A 462 MotherBoard - AMD KT400 - eBay (item 330522411182 end time Jan-27-11 14:04:48 PST)
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