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Optiplex GL+ 5100 motherboard looks dead

SomeGuy

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I'm guessing the motherboard is just shot, but I'll ask just in case.

I have a Dell Optiplex GL+ 5100 Pentium 1 system that was working fine last year when I tested it. It was great for running NT 3.51 and the QNX 1.44mb demo disks.

When I try to power it on, if I press and hold down the power button the hard drive and CD drive spin up, but the motherboard just sits there doing nothing, and when I release the power button the power instantly shuts off.

If I hold down the power button and press the reset button I get a beep code - three long and two short. The motherboard doesn't seem to do anything else, I get no video, and I don't think it is doing anything with the keyboard.

It has a fairly fresh CMOS coin cell battery, I think I put that in last year. Of course, I tried taking it out to see if it would reset anything. No luck there. Also tried it without any ISA cards installed.

I don't know what that beep code means for this specific machine, but various sites equate that to a memory error. I also tried switching around the RAM chips and tried some other ones. No luck there.

The power supply is not a standard ATX, although it uses an ATX plug. So I don't have any other power supply to test with. Although since the hard drive and CD drive seem happy until I release the power button, it doesn't seem like a supply issue.

I think it has a Pentium overdrive installed in it, but I never did write down the details.

Any ideas? At least any confirmation of what that beep code means here?
 
Check for bad capacitors.

But it could be just dead Jim. i've got a few mobos of various types that exhibit similar symptoms I've had no luck getting life out of.
 
I can only find one picture of the motherboard on the internet, but it looks like it has SMD electrolytic capacitors on it. I would suspect those have gone bad and are causing problems, because SMD capacitors from the 80s and 90s universally had problems with the rubber seals failing and causing the capacitor to leak and/or dry out and fail. Since the base of the capacitor has so much surface area, the electrolyte tends to wick under the capacitor instead of leak out, so the only way to know if they're bad is to remove the capacitors and replace them.

Another area I would look at is the power supply, PSUs of that vintage also have capacitor issues and should be checked. Remember that a failed capacitor won't always show physical symptoms, they can have any number of issues and not show any outward signs of failure. You can remove the capacitors and check them one by one, but it's easier just to recap the whole unit so you have a known good starting point.
 
I collect older Dells, 3 long 2 short is memory. Clean the memory edge connector on the ram and the slots. Wiggle em a few times after you clean them. Should fire up.

Sometimes just wiggling the ram works, My XPS 166 hates being moved and have to do this every dang time. Ill clean em next time I use it, just been lazy. My XPS 90 (with fdiv bug) used to act the same way, till i finally got annoyed and cleaned the ram and slots with some QD Electronics Cleaner. They cheaped out on the memory slots after 486s till pentium 3. If I had to guess I say they warp a tad. Or maybe the fit of ram is just slightly too tight and ram warps, I dunno -- *shrug.

In any case, wiggle the ram a few times and see if she boots. If not, repeat again a few times. If that dont work then clean and try again.
 
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That assumes the memory modules are good. Memory can go bad just sitting, so unless it can be tested in a known good machine, assuming some memory sticks are good can cause you to chase your tail for hours.

If the system uses SIMMs, bad contacts are less likely since both sides of the module are the same, and both sides also contact the memory slot on both sides. What can cause issues is if the retainer clips are bent or broken, which won't put the correct pressure on the module.
 
Thanks for confirming the beep codes. I did clean the board and the RAM, but there was no change.

On other similar Dells where there is a memory problem, do they also shut off when releasing the power button, like this one is doing?
 
Thanks for confirming the beep codes. I did clean the board and the RAM, but there was no change.

On other similar Dells where there is a memory problem, do they also shut off when releasing the power button, like this one is doing?
Yes they do, but only when it doesn't fully boot. Sometimes its beeps, sometimes it uses the power led , and blinks red for the codes, depending on the machine. It bothers me that its not showing any life though. How many sticks of ram are installed? The machine doesnt have dual channel, so try to only boot with 1 stick. Also the machines are picky on ram. Can you provide photos of the ram stick(s).

Also do you have another power supply to just rule that out?
 
I swapped a power supply from an Optiplex GX1 into a non-booting GXMT 5133 on a whim and had it work, which I believe is of similar vintage. I suspect they were using that custom psu pinout for some time. Also means there's a chance that the Athena Dell psu adapter would work for testing with a standard psu though I would give the pinout a good check before trying.
 
I was thinking about this, as I was cutting up protoboard to fix my Pentium Pro build. The case is same era, and has an almost exact copy of the dell power board in it. I cant use the original one, due to it causing the same exact problem you are experiencing. When I pulled it off the chassis it works fine. Somehow its sharing ground with the case, and the board hates it. Now im wondering if some electrical tape and nail polish fix the problem. Hrmmm... :unsure:

Do me a favor and pull the front of the case off and unscrew that small pcb with the power button and leds. See if it will start normally then.
 
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