Dead eMachine

[cjackson]

Working on eMachine T1742 (ca. 2002). Would not power up. Found a bad 250W power supply. Replaced with 300W power supply. Had to add a 4-pin
+12VDC plug for mobo (IM845FL). PC power comes on immediately, without pressing the power switch, as soon as power cord plugged in.

CPU fan comes on; PS fan runs. All voltages on mobo plug present. Cannot shut down the power. Nothing is working. No display, no lights on CDROM or floppy drive, HD. (Replaced EPROM battery for Bios chip.) I know that there should be a power-up sequence and that newer PCs use a 'soft power' sequence, starting with a 'Power On' signal from the power switch, followed by a 'power good' signal from the mobo to the PS.

Any ideas? Possible bad mobo? Bad replacement ps? Thanks for any help

[mjc]

Could be a short or a bad motherboard...or something else.

Have you tried stripping it down to just the power supply and motherboard?

[azzey]

Take the motherboard out of the case to rule out a short circuit. Where there any hardware/software changes before this happened?

Any beeps or fans spinning? If you leave it for a while, does the CPU heatsink get warm?

[cjackson]

Running just the motherboard. This machine was 'donated' to our Senior Center. We take donations, fix them and then send them on to charities. The previous owner said it worked, but I doubt it. The monitor also was supposed to be working, but the on/off switch had been smashed and it's on all the time.

I've measured all the required voltages at the motherboard -- + 3.3, +/-5, +/- 12, 'Power OK,' 'Power On,' etc. and they are all OK. Can't check out the chain of events on turn on without a scope. I'm thinking that something went wrong with the motherboard, which took out the power supply.

Thanks for your suggestions.

[cjackson]

Motherboard was bad. Found several cases on Internet where the eMachine mobo (Trigem IM845GL) took out a power supply )or vice versa. No need to work further. Will replace mobo with anoter. Current PS is OK. Thanks for your input, folks.

CFJ