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Author Topic: 20 pin power supply used on a 24-pin board  (Read 3227 times)

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DaveLembke

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20 pin power supply used on a 24-pin board
« on: March 02, 2019, 12:18:56 PM »
So my main computer last night lost its power supply which was a Rosewill Bronze 80 Certified 450 watt power supply that I got for free and lasted me 2 years of daily use and prior owner a year or two before I acquired it. Went to swap out the power supply and noticed that the Corsair CX450 that I had brand new as a spare power supply to drop into whatever system I had needed a power supply for only had 6-pin 12VDC for CPU power connection and not the 4-pin that I needed.

Tried to plug it in where 2 pins hang off the side unused to make use of 4 of 6 pins but the connector wouldn't allow that.

So I went to a older Core 2 Duo HP Pavilion I had that I knew had a good power supply and it had the 4-pin 12VDC CPU power molex. Opened it up and to my surprise HP manufactured this system with installation of a 20-pin power supply plugged into a 24-pin motherboard with the 4 other pins with nothing plugged into it.

Doing research in how could this have worked, I found that the 4 pins added to the 20-pin legacy type P4 era power supply were added for better PCIE-16x power, and that if your running integrated video you dont have to worry about running a 20-pin power supply on a motherboard with 24-pin connector. However the computer I had given to me from someone who said it wasnt reliable and was randomly crashing during games. They stuffed a Geforce 9800 GT video card into it in the PCIE-16x slot.

Well I guess I know now why their computer was crashing on them since the power supply was just a 20-pin and not a 24-pin to handle the load of a video card in the PCIE slot.  ::)

Nice of HP to do this back then with the Pavilion to cut costs in manufacturing was my thought on what I discovered. Although I have seen other transitional period legacy parts used before with newer components with 4-pin molex to SATA power adapters etc in systems like eMachines and older Gateway PC's etc, but never seen a system that has a 24-pin motherboard power connector run on a older Pentium 4 era 20-pin power supply before, so it was an interesting discovery as well as now I know why that computer was likely having the issues it was having for the prior owner.  ::)

So I was faced with either having to order another power supply that had the now legacy 4-pin 12VDC CPU power molex connection or buy an adapter to plug between the 6-pin and motherboard to convert it to 4-pin.

However, I was looking at a leg of the power supply that was a legacy leg with the older 4-pin molex ( 5VDC, Ground, Ground, 12VDC ) and since my system was a low power consumption system with its AMD A8-5545m APU in the ITX motherboard, I decided to take a old 4-pin Y-Adapter and cut the 2 female plugs off of it and cut the 12VDC 4-pin CPU power molex off the dead power supply and connect the yellows to yellow and blacks to black and heatshrink to insulate the connections and so I am powering the 12VDC CPU power off of the legacy 4-pin connection with the 5VDC wire cut off because unused and a small section of heatshrink to cap off the nub of wire end from the male 4-pin connector.

Booted the system up with the Corsair CX450 power supply and all better with my homemade 12VDC CPU power connector from legacy 4-pin p-connector molex.

Figured I'd share this here in case anyone else gets into this situation of an older unstable computer after video card added causes issues to check to see if the power supply is a 24pin connection to the motherboard or if the system has a 20-pin older Pentium 4 era power supply powering it which was fine before video card upgrade but now with video card upgrade system starts to have stability issues. However my guess is that this period of manufacturers stuffing older power supplies into newer builds was short lived and as a means of mainly cleaning out excess inventory of older power supplies as a cost cutting measure and maybe this HP Pavilion tower is a rare find to find that Pentium 4 era power supply with 20-pin connector stuffed into 24-pin motherboard.

I'd suggest that if anyone lacks the proper CPU power connector to buy an already made adapter to convert to legacy -or- get a power supply that has the proper 4-pin 12VDC CPU power connector vs making their own. There is the risk in making your own adapter that you could damage your computer if you dont know what your doing as well as it might not be reliable if the CPU is power hungry and the 12VDC from the legacy daisy chain of 4-pin molex P-connectors cant handle the current demand. Since my build is a low power consumption Mobile APU in a Desktop board I figured it was safe to feed it its needed 12VDC from the legacy connection 12VDC tap. * Additionally a long time ago manufacturers like ASUS made gaming motherboards that didnt have the 12VDC 4-pin molex connection for the CPU power as a 2x2 square connection which became a standard, but had a direct 4-pin male P-connector on the motherboard to use the 12VDC off of this now legacy 4-pin ( 5VDC, GND, GND, 12VDC) type P-connector. So I felt comfortable going this route for my 12VDC CPU power need based on the fact that ages ago some power hungry Pentium 4 CPU's such as the 2.66Ghz that I worked on for a friend which was a first generation ASUS Pentium 4 gaming board manufactured before the 12VDC 2x2 4-pin standard ran fine off of this 12VDC power connection.