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Dell Optiplex 433/L Restore

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First post, by Intel486dx33

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Restoring an old Dell Optiplex 433/L ( Intel 486dx-33)

I worked on this before and I think I might have shorted something out messing around with the IDE cables and sound card.

I get NO video. It use to work. Video was working fine before. But now I get no video.
I tried an ISA video card but still no video.

I disconnected all the IDE/Floppy ribbons and removed the ram, but still no video.
It does not even beep and error codes.
I see the keyboard lights work on power up.
but I don't think it is posting as I don't hear any beeps.

I could not find a manual on this computer.

The motherboard does have silkscreen labels for the jumper settings.
I reset the bios and tried to disable the onboard video and use an ISA video card. but no luck.
I put a NEW battery in it.

Do you think something is shorted on the motherboard ?

It sounds like it is booting when I turn it on.
I hear the drive spin up and reading.
power supply and power switch appear to be good and working.

What do you think ?

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Last edited by Intel486dx33 on 2018-08-30, 07:46. Edited 1 time in total.

Reply 1 of 20, by gca

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I got one very similar to that but its the 466/L (66Mhz), same chassis and motherboard I believe just a different processor.

Mine is also dead sadly but I have a rough idea what is wrong with mine. Looks like a resistor on the power chain to the RTC IC (5v up to that resistor but only getting 2v out, the RTC IC needs 5v so I will have to swap that resistor out (assuming I'm right, just playing it by ear as I don't have a board view or schematic)).

Quick question, is the CD on the same IDE chain as the HDD or is it plugged into an expansion card of some kind. Mine only came with a floppy and as mine is dead I haven't been able to experiment with it yet.

Reply 2 of 20, by Intel486dx33

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Yes, Thats how I messed mine up. I was trying to add a CD-ROM drive on the same single IDE channel.
The best way to add a CDROM is with a dedicated controller, either on a sound card or ISA controller.
The bios does not support CDROM. So it wont pick it up.
Do you have any documentation for this computer ?

Reply 3 of 20, by gca

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Sorry no documentation at all for that machine apart from the data sheet for the RTC IC which I got from the components manufacturer.

Have you tried swapping out the processor on yours? I have seen similar symptoms on newer dells (GX280) where the machine is completely catatonic due to CPU failure.

Reply 4 of 20, by Intel486dx33

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Okay, I will have to put this project on hold for now.
I will have to get back to it and check all the capacitors, resistors, and diodes with a meter.
Some day when I have time.

Reply 6 of 20, by gca

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Thanks for the offer sirlemonhead, my problem appears to lay with the RTC power chain.

Tracking it back as best I can I get this (also see rtc-power-chain.jpg).

AVDD (pin 16 on rtc) -> C108 -> C42 -> R135

These should be running at 5V I think (based on rtc ic data sheet that indicates that AVDD is a 5V pin) but all I am getting is 2.2V. No idea where it goes from R135 as this is as far as I could trace it with a continuity meter (you may have better luck).

VDD (pin 4 on rtc) should be running at 5V but its getting 2.2V like AVDD so, maybe they share a common power source? I don't know I couldn't trace it.

Noticed that C87 (up by the motherboard power connectors) is giving 0V output so it might be a good idea to give that a check to see what you get. No idea if its related to this problem or not.

Also attached the RTC data sheet if thats any help.

And it doesn't make any difference if the rtc battery is installed or not, either way the voltages are way lower than expected.

PSU voltages are fine, I tried the PSU in another machine and everything worked as expected so that isn't the problem either.

Thanks in advance for the help.

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Reply 7 of 20, by sirlemonhead

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I'll try get to this as soon as possible...

Not to do the typical "It's old! CHANGE THE CAPACITORS!" thing, but I do notice the solder joints around the SMD caps on my board are really dull looking, and yours appear to be the same... Are they leaking do you think?

Reply 8 of 20, by gca

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Caps is a possibility but I have no way of testing them.

The machine was working (obviously, dell didn't ship a dead unit (I hope)) but power up was intermittent. It would turn on and boot once, if you had to power cycle for some reason the machine was just completely catatonic when you tried for a second power up, no beeps no nothing.

I did manage to get into a boot up diagnostic (no idea how) which indicated the clocks weren't syncing (or words to that effect) which is why I started checking the clock chip for issues and found the incorrect voltages.

No rush, you get to it when you have the time.

Reply 9 of 20, by sirlemonhead

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So... seems my board is different!

I don't have the same RTC chip, and where yours is, is unpopulated on my board. I'm using the spot right beside it on the board, which has an avafem av9155 chip. It's getting 5v on it's VCC pin.

The capacitor and resistor you show in your photo is not populated on my board.

C87 also gives 0v on my board.

I have some bad photos I can upload later if they'd be any use 😀

Reply 10 of 20, by sirlemonhead

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Also, FYI - I'm running a standard ATAPI CD-Rom and IDE hard drive on the same cable to the boards lone IDE port. The BIOS on these old machines will never detect a CD-ROM drive - the driver and MSCDEX takes care of getting it working.

Set HDD to Master, CD-Rom to slave. HDD on connector on cable that's closest to motherboard connector, CD-ROM on the other end.
Drive 0 in BioS set to your HDD settings then leave Drive 1 set to "Not Installed"

Then just get your cd-rom driver and mscdex and set it up in config.sys etc as usual.

Reply 11 of 20, by gca

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Strange, esp as they are the same model. I'll get a photo of my board tomorrow and post it then we can see just how much they differ. I assume they changed the design at some point in the models life and we have different versions.

Semi relieved that C87 is 0v on both, so I assume I can rule that out as being relevant to the problems I'm having.

Shame I can't find a boardview anywhere (machine is probably too old for one ever to have existed) that would solve so many problems.

Reply 12 of 20, by gca

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I had a few moments and got a photo of the board in my machine to compare to yours. And I re-checked the nameplate in case I misread it to confirm it is most definitely a 466/L.

Two notes on mine, I have the VRAM and L2 cache upgrades which explains the daughter boards above and to the right of the processor respectively. Both of which were removed during troubleshooting so we can rule them out as the culprits.

Also found the photo I took of the on board diagnostic results. Still have no clue how I got this running (maybe automatic, if so why hasn't it shown up again?) which shows something is very wrong on the timing front.

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Reply 13 of 20, by sirlemonhead

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Cool! I don't have the cache upgrade for mine. Did yours always come with it?

I need to borrow a better camera before I try take more photos as mine aren't coming out great - I have quite an old phone. Will get back to you..

Reply 14 of 20, by bjwil1991

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Bad capacitors, cold or cracked solder joints, bad traces, and a bad PSU (test it on another machine, but, Dell used its own proprietary PSU connectors, or check for voltage dropouts).

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Reply 15 of 20, by gca

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The machine had both cache upgrades when I got it. Whoever the original owner was they maxed it out with both video and L2 cache.

As for the PSU, it appears to be a run of the mill AT unit. Pin out is the same of every other PSU I've come across. And I have two for this model of machine both check out ok, voltages within normal range and work fine on other AT boards.

Caps are probably the culprit but figuring out the exact power chain is going to be problematic without a schematic or boardview to go by. Probing around testing for continuity only got me so far. I don't see any cracked joints but I'll give the board a more thorough going over when I can to rule that out.

Reply 16 of 20, by gca

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Not sure if this will be much help but I found a list of all the part numbers of the machine. At least it yields the part numbers for both OEM and IBM parts (not sure why, did IBM use the same board somewhere?) which might pin down a viable schematic or boardview.

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Reply 17 of 20, by Intel486dx33

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gca wrote:

As for the PSU, it appears to be a run of the mill AT unit. Pin out is the same of every other PSU I've come across. And I have two for this model of machine both check out ok, voltages within normal range and work fine on other AT boards.

Caps are probably the culprit but figuring out the exact power chain is going to be problematic without a schematic or boardview to go by. Probing around testing for continuity only got me so far. I don't see any cracked joints but I'll give the board a more thorough going over when I can to rule that out.

Thanks for the info and update. Please keep us informed as to your progress if you wish to continue.
Some day when I have time I might get around to checking all the Caps, resistors and diodes on my motherboard too.

Reply 19 of 20, by Niezgodka

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Sorry for microwaving such an old thread, but I have 433 LV. It works, but once or twice it died on me (no display, keyboard blinks, fan spins). Not sure why 🙁
PSU seems to have different markings (it is p4 and p5), and I'm not sure if I can plug regular P8 and p9 connector into it.
Question, can you upgrade its CPU with just sliding 486DX2 or DX4?
Also, does anybody know how to get to bios in it?