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| Thread ID: 39972 | 2003-11-23 21:51:00 | Power Supply or MB or??? | B.M. (505) | Press F1 |
| Post ID | Timestamp | Content | User | ||
| 194225 | 2003-11-23 21:51:00 | Whilst loading Office XP over Office 2000 on a Win98se Machine the machine turned itself off! Yep closed down everything. I restarted the machine (turned power off and on at wall) and the machine loaded as far as the splash screen and just closed down. When I say closed down I mean everything, fans including power supply fan everything. No amount of pushing the on on/off switch will breath any life into the machine. However, if I power off at the wall connection, then power on, and push the on/off switch on the computer, the power supply fan now does a couple of turns and everything dies again. Initially, I blamed Office XP for loading files that closed down the computer, but then I thought that might just be coincidence. Thinking, it may be a power supply failure I removed the power supply and fitted it to another computer I keep for such purposes, and the whole thing ran perfectly. I then restored the power supply to the original computer and no go. (at least the fault isn’t intermittent!) The only conclusion I can come to is that the Motherboard is shutting down the power supply via the Power Made Good wire? Oh, I’ve also disconnected the power to the HDD & CD ROM leaving only the floppy connected without relieving the fault. Anyone any thoughts??? The MB is a VA6, Power Supply 400w Hairong, Processor Pentium 3. |
B.M. (505) | ||
| 194226 | 2003-11-23 21:54:00 | it could be that a fan on the motherboard is noit runnign and so the bios wont let the system start. otherwise i would point the finger at the motherboard. |
robsonde (120) | ||
| 194227 | 2003-11-23 22:57:00 | seeing as it dosn't get to OS loading stage its a hardware problem . strip it down to the basics, cpu ram vid and psu . if still no go then start swaping parts out . also i would check bios settings . |
tweak'e (174) | ||
| 194228 | 2003-11-23 23:10:00 | I had a P3 with similar problems and I discovered that the CPU had managed to half work itself out of the CPU socket. So check to make sure CPU is fully inserted. Also check if your video card is firmly in the slot, and that all cables are connected properly |
Chao is back (634) | ||
| 194229 | 2003-11-24 00:07:00 | Well the plot thickens . I thought I’d check the CPU fan as Robsonde suggested and that is the same as the PSU fan . A couple of turns and it’s all over . We have power for less than one second . So, as the original power supply worked fine in the standby machine I thought I’d try the stand-by’s power supply in the faulty machine and stone the crows if it ain’t still running . I’ll now be able to check the BIOS settings, but I’d be surprised if they had anything to do with the problem, as we never had power long enough to get to the P . O . S . T . procedures . Maybe the 250 watt power supply is less sensitive to whatever is shutting the other one down? Any further ideas? |
B.M. (505) | ||
| 194230 | 2003-11-24 01:24:00 | i assume you have removed all unneccary parts? i've had faulty modems do a simelar thing. i would suspect RAM first, cpu 2nd and motherboard 3rd. make sure your useing a known good vid card. ram is proberly the easyest to swap out and check. |
tweak'e (174) | ||
| 194231 | 2003-11-24 01:59:00 | When you swapped the power supplies, you unplugged and replugged the IEC power cords. Some of those moulded plugs are "not very good". :D If they work their way out a bit over time, you can get a very poor contact. |
Graham L (2) | ||
| 194232 | 2003-11-24 02:44:00 | The bit that’s got me is both machines work fine on one power supply but the machine that went faulty straight out refuses to work on its original power supply. I swapped them back and forth half a dozen times now. I can’t even measure the voltages, as the digital voltmeter doesn’t get time to settle before shutdown. An analogue voltmeter is even worse. I know these power supplies are designed to shut down if certain voltages don’t meet certain limits within a period of time but I didn’t think that period of time was less than a second? I’ve overcome the problem by leaving the power supplies swapped and both machines are as happy as Larry. (For the meantime anyway) Yes guys I’ve checked the power cords, the CPU, RAM etc and all seem correctly seated. Surely if the problem was one of them it would be common to both power supplies? Can anyone tell me what comes down that Grey “power made good lead”? Is there any way to tell whether a signal down there is causing the almost immediate shutdown? |
B.M. (505) | ||
| 194233 | 2003-11-24 03:01:00 | I assume you mean the "Power OK" lead. That should be a logic "high"(+5V) a few tens of milliseconds after all the DC outputs are at the correct level. It should go "low" (0-0.4V) some tens of milliseconds before the supplies go outside their tolerance (usually when going down because the mains has gone away). Some cheap supplies probably just tie it to the +5V supply. :D When it's low the motherboard holds the CPU in the Reset mode. |
Graham L (2) | ||
| 194234 | 2003-11-24 04:01:00 | Thanks Graham, Well, not having an oscilloscope at my disposal that makes things a little awkward doesn’t it? What was wrong with a 1000 amp knife switch? If you had a problem the smoke indicated where! :D |
B.M. (505) | ||
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