# Basic power supply and/or motherboard troubleshooting with a multi-tester? **URL:** \ **Category:** Factual Questions\ **Created:** [November 25, 2007, 5:05pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711 "2007-11-25T17:05:59Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [November 25, 2007, 5:05pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/1 "2007-11-25T17:05:59Z")
My main PC is down, and I’m pretty sure I’ve got either a bad power supply or a bad motherboard. Are there any basic tests I can run with my multi-tester that will rule one or the other out? It’s an HP m7167c, with an ASUS P5LP-LE mobo and I’m pretty sure a relatively standard ATX power supply (300W). Thanks in advance! ---
**Author:** ![Myglaren](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@Myglaren](https://boards.straightdope.com/u/Myglaren)\ **Post date:** [November 25, 2007, 5:45pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/2 "2007-11-25T17:45:22Z")
There is a thread touching on this open here: [http://boards.straightdope.com/sdmb/showthread.php?t=444302&highlight=computer+power+supply](http://boards.straightdope.com/sdmb/showthread.php?t=444302&highlight=computer+power+supply) including this which may be all you need to know: > [@](#): > > Or you can just use a paper clip. Disconnect the PSU from the rest of the machine but leave it plugged into the outlet. On the 20- or 24-pin motherboard connector, there should be many colored wires; the green one is the important one. Use a paper clip bent into a V to connect the pin at the end of the green wire (PWR ON) to any pin at the end of a black wire (GND) – this simulates pressing the ON button without interference from an actual button or a motherboard in the way. If the fan spins up, you have a working power supply and it’s your motherboard. I take no responsibility if you should happen to electrocute yourself. ---
**Author:** ![Will\_Repair](https://avatars.discourse-cdn.com/v4/letter/w/a698b9/32.png) [@Will\_Repair](https://boards.straightdope.com/u/Will_Repair)\ **Post date:** [November 25, 2007, 7:33pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/3 "2007-11-25T19:33:10Z")
> **[ATX Mother Board Main Power Connector Pinout](http://www.interfacebus.com/ATX_Motherboard_Main_Power_Connector_Pinout.html)** > > PC ATX Motherboard Pinout Main Power Header, connector style and Part Numbers, Wire sizes ---
**Author:** ![Gorsnak](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gorsnak/32/7587_2.png) [@Gorsnak](https://boards.straightdope.com/u/Gorsnak)\ **Post date:** [November 25, 2007, 7:41pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/4 "2007-11-25T19:41:15Z")
A PSU can spin up its fan and still be bad. To check it slightly more thoroughly put a load onto it - plug a hard drive in, for example - fire it up using the paper clip method and then use the multimeter to check the voltage on the 12V and 5V rails. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [November 25, 2007, 11:13pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/5 "2007-11-25T23:13:59Z")
Thanks, y’all! ---
**Author:** ![Jurph](https://avatars.discourse-cdn.com/v4/letter/j/50afbb/32.png) [@Jurph](https://boards.straightdope.com/u/Jurph)\ **Post date:** [November 26, 2007, 2:56am UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/6 "2007-11-26T02:56:58Z")
[QUOTE=Gorsnak] A PSU can spin up its fan and still be bad. To check it slightly more thoroughly put a load onto it - plug a hard drive in, for example - fire it up using the paper clip method and then use the multimeter to check the voltage on the 12V and 5V rails. [/QUOTE] I’ve got a multimeter down in my electronics graveyard, but strangely never thought of adding a load to check the rails. :smack: I’m definitely adding this to my standard operating procedures when I suspect a flaky PSU. Thanks a bunch! ---
**Author:** ![KP](https://avatars.discourse-cdn.com/v4/letter/k/a9adbd/32.png) [@KP](https://boards.straightdope.com/u/KP)\ **Post date:** [November 26, 2007, 9:30pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/7 "2007-11-26T21:30:20Z")
One of my “ongoing projects” (I bought the parts, but Lord knows when I’ll build it) is a computer power supply load tester. I mention it here, because if others take it up or make suggestions, I may actually finish it this winter. It seems like almost everyone I know hits a possibly dying PS every year or two – and guess who they come to? There are go/no-go testers for $15 or less, but its hard to trust them when you can’t confirm them, and they offer precious little in the way of specs or docs, even if you call the manufacturer. Phase I is easy: a series of mobo power sockets scavenged from dead mobos, wired in parallel to variable high current resistors ([nichrome wire](http://www.wiretron.com/nicrdat.html) strung between ceramic posts). Resistance is calibrated by marking various points with measured hot ohms @3.3/5/12V. Hot vs Cold ohms (high initial draw) turned out to be an issue. I stopped development to think of a more elegant way to deal the change in resistance than sliding an alligator clip from an initial “warm up” position to a final “test” position on the nichrome Test: Measure the voltages with the resistances set to draw, say, 75% of rated current on each rail. I think this alone should detect almost all bad PSs. Phase II: add some fast high current transistors (or similar) to short out part of the nichrome to simulate transient load jumps/drops of 1-4A (e.g HDD spinups) Phase III: since I don’t own a multiGHz scope at the moment, build a “trigger box” with a cheap high speed logic chip to latch an LED if hi/lo transients are present. By adjusting the sensitivity, I could compare the transient levels of a “known good” PS to the one under test. I’m not sure how much this would add in detecting normal failure modes, but this might tell me the answer, and it’s a LOT cheaper than a GHz scope I estimate the total parts cost of ~$20 (I used a lot of salvaged/junkbox parts, but the nichrome and ceramic posts were just a few bucks), so pretty much any hobbyist should be able to build it, using basic safety precautions. The output side is low voltage. A short to line voltage is extremely unlikely, but should immediately blow the PS fuse on testing. Any thoughts or suggestions? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [November 26, 2007, 9:57pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/8 "2007-11-26T21:57:56Z")
Sounds like a winning idea to me, **KP**! Alas, I’ve decided that discretion is the better part of valor where my main box is concerned, so I’ll be taking mine to a shop this week to let a pro deal with it. It’s getting too close to Christmas for me to spend any more time without access to Quicken. ---
**Author:** ![Myglaren](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@Myglaren](https://boards.straightdope.com/u/Myglaren)\ **Post date:** [November 26, 2007, 10:01pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/9 "2007-11-26T22:01:39Z")
Try swiping a friends power supply and hooking it up to your box, no need to install it. Would take around ten minutes to verify if it is the power supply or not. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [November 26, 2007, 11:54pm UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/10 "2007-11-26T23:54:03Z")
You have significantly over-estimated the number of friends I have, **Myglaren**. ---
**Author:** ![ZipperJJ](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zipperjj/32/211_2.png) [@ZipperJJ](https://boards.straightdope.com/u/ZipperJJ)\ **Post date:** [November 27, 2007, 12:17am UTC](https://boards.straightdope.com/t/basic-power-supply-and-or-motherboard-troubleshooting-with-a-multi-tester/427711/11 "2007-11-27T00:17:36Z")
[QUOTE=KneadToKnow] You have significantly over-estimated the number of friends I have, **Myglaren**. [/QUOTE] Go buy one at a store that will let you return it if need be.