eMachine 620 (UK) PC, fault with PSU and USB ports?

JLamy

Hi peeps.
I have just revived my friend's PC made by eMachines. I am told that the machine went "funny" then wouldnt switch on at all. When I plugged it in the mains, the PC went on at half power (less fan noise than usual, with the hard disk LED at 50% usual brightness in a flickery state). I changed the PSU for a spare working one, and that had fixed the problem of not being able to be switched on. However, I am left with two abnormalities. Firstly the USB ports on front of machine and on the motherboard don't work anymore. Everytime I plug my working USB flash drive in a port I get "unrecognised device" error. This flash drive has been used in this PC before, without problem. The flash drive itself is still in good working order as I tested it using my other systems. I thought it was a corrupt USB driver issue, so I fresh installed Windows XP Pro SP2 onto another partition to see if this was the case. The same problem remains, only this time XP displays a bubble message telling me a USB device is using up more than available power in the ports. The message remains even if I remove the flash drive and click reset button. This message also remains after I reboot - only way to stop it is to disable a USB system device (hub) in Device Manager. I have checked the USB headers on the mobo, and they all seem to be plugged in right. I then installed SP2 onto the original Windows XP Home install (it was XP Home Edition SP1), it went ok but now my USB error message is no longer the unrecognised device, it is now the same as the Windows XP Pro SP2 message of a USB device is using up more than available power in the ports.

I am thinking, could the original failing PSU damage the USB part/circuit of the motherboard in some way during the time when PSU was faulty running at 50% power? Or is my spare PSU faulty in the powerline that provides power to USB part of mobo.

My second problem relates to the fan inside the PSU. When the system is shut down, everything is off apart from the fan in the PSU which doesnt seem to turn off for however long I leave the machine in this state so i not think it thermostat related. Also, the hard disk LED light is on at 50% of usual brightness in a flickery state whenever the system is shut down from Windows or the power button. The hard disk LED light works correctly after system POST when system is switched on. Another strange thing is that the power LED stays on at 50% usual brightness IF I FORCE a system power off by depressing and holding down the power switch for 5 seconds. The power LED is completely off when shutting down from Windows. All LED wires are correctly wired to the motherboard pins.

Does my 2nd problem point to a faulty PSU or faulty motherboard circuitry caused by the failing PSU?

Any iideas, thoughts or solutions welcomed, please.

Zuntar

Wow, sounds to me that the failed PSU damaged the mobo, which could cause the symptoms you have described.
With the second problem, the second known good PSU is the one acting that way? If so, try unpluging it from everything (or take it out all together) and jumper the green wire to the black wire right next to it (that should allow it to turn on) and see what you get. Does it turn off now? What do the voltage rails measure?

kryyst

Sounds like it's not shutting off and it's only going into standby mode. Try turning it off by pushing in and holding down the power button for about 10 secs or so is should eventually turn off - fully off with nothing running except perhaps an led for the mobo meaning basically that it's plugged in and perhaps a NIC light.

JLamy

Thanks for the comments. Unfortunately the PC has broken down again last night. It was doing a disk check before a defrag and then click - screen went blank, green LED off, HDD light flickery on but wasnt doing anything. Presing power button did nothing so I turned it off completely by unplugging from the mains, waited a minute, plugged back in. The system now behaves exactly how it did before I "fixed" it by changing the PSU. Just the HD LED is on flickery. When I press power button the DVD-ROM drive powers up but the CD-RW drive doesnt! I think the 2nd blow out damaged the CD-RW drive. At this point I'm thinking either my PSU was faulty, or something on the mobo caused the PSU to blow so today I went out and bought a cheap PSU just to see if it would make the machine work again. I wired up the new PSU, the PC still doesn't work - exactly the same symptoms as the previous PSU I put in. Unless the new cheap PSU is faulty too, which I doubt. I not have the knowledge to check the voltage output from a PSU, let alone have the equipment to be able to do this, like a voltmeter???

So, now I think the PC is really broken as in it could be the CPU, or something on the motherboard. Its some micro ATX mobo made by a company I not heard of, and mobo made exclusive for eMachines I have read. I sense a replacement mobo on way.....

kryyst

I doubt either of the last two PSU's are faulty. Most likely your mother board took the hit. eMachines aren't the most technically sound machines.

JLamy

kryyst wrote:

I doubt either of the last two PSU's are faulty. Most likely your mother board took the hit. eMachines aren't the most technically sound machines.

Hehe, yeah I would agree with you on that, as all their systems are of a comparatively low price. But how come when I changed the old PSU to my PSU it worked for a while?

Looks like I'm in the same boat with the people in this thread.
http://computing.net/hardware/wwwboard/forum/37378.html

kryyst

Yeah generally (my own experience) when a PSU goes due to just equipment failure everything else is fine. However when a PSU is blown due to a power surge it often will take out the mobo and/or the cpu and/or ram plus I've seen it take out harddrives also. It's kinda hard to diagnose it exactly in this medium because the symptoms of failure for a dying mobo, cpu and ram are all similar and the only way you can narrow it down is trial and error.