DELL PC Power Problem

I know this isn't a PC forum, but I'm at a loss and there are some pretty good minds on this forum. This is a PC hardware question for a Dell XPS400. I shut the pc down normally and unplugged it from the wall. When I plugged it in again it would not start. Nothing. No power light, no diagnostic lights. NADA, ZIP, ZERO. verified it was getting AC power to the supply. the front panel power switch is OK. I checked continuity at the motherboard end of the front panel ribbon cable and there is a good switch closure. The power supply checks out OK. I removed the main power connector from the motherboard and grounded the PS-ON signal and measured all the supply lines. All were healthy including the PS-OK signal. I removed the PS-ON line from the connector and plugged the connector back in to the motherboard. I grounded the PS-ON line to see if I could get it to boot. The power supply came on, the diagnostic lights went through their sequence and the diagnostic and power lights went off but the hard drive light stayed on solid. I monitored the PS-OK line and it remained at 5Vdc (PC OK condition). Do any of you guys out there know anything about the power control logic on Dell machines?

Do you get any video? Power on self test ? Any beeps ?
If you do not get video, it could be memory or CPU, if you do get video in console form, try to enter the BIOS setup screen, there you can see if BIOS recognizes the correct parameters including HDD, memory . . .

No video. no beeps. Diagnostic led's as described.

There's quite a couple of thing making a PC hang @ start up. What I sugest is to disconnect everything (USB, Hard Drive, CD Rom...), remove the RAM sticks, reset the mother board, re-install the RAM and try to boot it again. If it doesn't work... you may have faulty RAM, CPU or Mother board.

Also, make a visual inspection and Check if there's any "popped top" Electrolytic on the mother board.
http://ludens.cl/Electron/chinverter/21cap.jpg

HTH

I've done all of that. The supplies are all within spec with the configured load applied. What I was curious to find out what the interface circuitry on the mother board is between the "power" switch and the actual PS-ON signal that turns on the power supply. Does it come from a CPU I/O line or some peripheral glue logic? Is there a source of board schematics anywhere on the web that you know of?

Ed

not that I know, sorry.

You should at least go to support.dell.com and enter your "express service code" or your "service tag" number and you should be able to get to very detailed teardown and re-assembly instructions. I used to be a Dell service tech contractor (module swapper, really) and taking apart a lap top is no small task. (at least if you want to put it back together again :)

I have not been to their website in quite a while... so if you can't find the teardown instructions let me know and I'll see if I can get you a better link.

I never did see any schematics there in all my time doing dell support.

good luck

Thanks for the suggestions. I was looking for information that apparently is not available to the public. I decided to bail and but a new machine. The old one was pretty old... :) I got an XPS8300 with the I7 processor (yes I checked the mfg date to be sure it was after Intels fix).

Thanks again

Ed

Sometime it just don't worth to spend too much time on old computers. I sat: Smart move!