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Compaq Deskpro 486/33M - An adventure

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NightShadowPT

Member
Joined
Sep 30, 2022
Messages
15
Hi everyone,

I have recently bought a Compaq Deskpro 486/33M because it was one of my first computers and I wanted to relive those times.

The goal was to upgrade it into a dream machine, but it seems I've hit a snag that I need to address before going on to the upgrades.

The machine arrived yesterday in perfectly working condition, and I have spent most of the day cleaning it up and started to configure my MS-DOS with all the required tools.

I could make everything work well and after a few benchmarks the performance was very solid - 10.1 on Player Bench, 24.8fps on Chris Bench and 37 fps on 3D Benchmark.
Ran a few games, including Doom that I could surprisingly run at full screen with acceptable performance and everything seemed to be going well.

Earlier today, something weird happened:

- while creating a disk from one of the softpaks (the one that contained the VESA drivers), the program gave a strange error - something about not finding a file - and aborted. To my surprise, when I tried reading any floppy disk, it was showing as empty.
- Thinking of it as just a temporary fit, I rebooted the PC, but it hang on boot (no video, no sound, nothing)
- Tried a few more times and on a few of the reboots, I got a long and a short beep, followed by the error "101-ROM Error" displayed on screen
- One of the reboots, the memory counter showed up - it finished the memory count, but then just a black screen

I kept trying to reboot, but the result was always one of these... :(

Anyway, I tried some basic troubleshooting:

- Tried removing the memory board - same result (sometimes counted the 4MB onboard memory and got stuck, other times the beeps and 101 error)
- Tried removing the video card - Got the beep error of missing graphics card
- Tried removing and reseating the processor board - no change
- Disconnected the HDD and both floppies - same result

Other noteworthy remarks:
- The Power supply seems to be working well - the fan spins and power gets to the components.
- No strange smoke or smell came out of the PC when this happened 😀

Not sure exactly what I can do at this point, and I am quite frustrated as this upgrade project has just turned into a troubleshooting one :(
 
Update:

After an endless loop of reboots that took me nowhere, I tried disconnecting the keyboard and that resulted in a message that the keyboard was missing, to press F1 (gotta love this message).
I connected the keyboard, pressed F1 and the PC booted normally.

Tried the same trick a few more times and nothing... stuck on boot or 101 error.

Gave it a pause and when I came back 1h later, tried booting it and it worked.

Used the opportunity to run the EISA configuration utility, just in case something was corrupted, removed and added a card - saved and... the computer seems to be back to normal.

Already rebooted it 10 times, and seems to be operating normally.

I have no idea what happened, how it got solved, but it makes me nervous as I don't like these weird things I cannot explain. Makes me feel like the problem can come back at any time... 🙁

In another forum someone suggested this erratic behavior could be due to cracked solder joints... if it shows up again, I will check for the cracked joints.

I will keep you posted of any changes.
 
Almost sounds power related, could be cracked solder joints but these boards are well made. I have a near complete one that I screwed up tryin to swap the bios socket on, because it cracked, and whole board puffed up like a pizza bubble. So be VERY careful with these boards and a hot air station.

In any event if you need a power supply I happen to have one, as well as a spare floppy drive, and case bezel thats in really good shape other then the badge. I would just try reseating the AT power connectors on the board first.
 
Also you may want to rerun a memory test, like memtest x86, just to rule out bad memory as well. If it does turn out to be memory, believe I still have some original Compaq sticks somewhere round here you can have for cost of shipping. These machines like dual sided FPM memory.
 
And today it has decided that it will not boot again..... aaaaaaahhhhhhhhh!!!!!!

Twolazy, maybe it's time for me to take you on your Power supply offer... I believe I can't yet contact you by PM because I am a new user... (can't see any options to PM you)...
 
One of the other options I would like to explore is the battery, but unfortunately I cannot seem to find the battery anywhere... the only place where it could be that I haven't checked yet is the IO board under the power supply because it is not easily accessible...

Anyone has any idea where that may be located?
 
Found it!! It's on the IO Board as suspected... it's a Dallas DS1397.

I’m weary of buying a new old stock part as the battery may be depleted by now…

I’ve seen a few replacement parts that will take CR1220 batteries on eBay , but they don’t seem to be for the same model.

Anyone knows where I can find such a part?

Thanks

62453E50-FF0C-418B-9366-E7835C6DCA93.jpeg
 
Dont use those cr2032 modules in the Compaq, as I believe it stores EISA infromation in the nvram on the clock chip (Ones you are talking about are DS1287 replacements, DS1397 have 4K x 8 sram). Upside, they are less then 15 dollars online. Batteries last on avg 10 years. Just make sure to throw a socket on it when you pull it off. Could try the battery mod on it like normal DS1287s as its essentially the same.

After replacement or mod, you will need to run the Compaq Deskpro /M 486/33M System Configuration Utility.

​

 
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Mine was doing the same thing where sometimes the system would glitch out or would not survive a hot power cycle. I found several caps leaked out in the power supply and just recapped the whole thing. It's a pain in the butt to get into the PSU because it's screwed in weird places but the recap seemed to of worked and it was fine after that.
I reused the original Dallas module by strapping a CR2032 socket on top.
 
twolazy said:
Dont use those cr2032 modules in the Compaq, as I believe it stores EISA infromation in the nvram on the clock chip (Ones you are talking about are DS1287 replacements, DS1397 have 4K x 8 sram). Upside, they are less then 15 dollars online. Batteries last on avg 10 years. Just make sure to throw a socket on it when you pull it off. Could try the battery mod on it like normal DS1287s as its essentially the same.

After replacement or mod, you will need to run the Compaq Deskpro /M 486/33M System Configuration Utility.

​

Click to expand...

So that is the reason why I cannot find a CR2023 module with the same number than my Dallas! Guess that's also why it says "Real Time RAMified" on the chip... :)
I will order a new one and maybe try to mod the old one later... could be an interesting project.

On the topic of a socket, it already has one... just need to pop it off and put the new one in.

My only concern is if the battery I buy online is really new, or just "new old stock", and that being the case it may no longer have any charge.
Do they even make new batteries?

Anyway thanks for the explanation. I learn every day...
 
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NeXT said:
Mine was doing the same thing where sometimes the system would glitch out or would not survive a hot power cycle. I found several caps leaked out in the power supply and just recapped the whole thing. It's a pain in the butt to get into the PSU because it's screwed in weird places but the recap seemed to of worked and it was fine after th
Click to expand...
Maybe I’m missing something, but my power supply seems to be ok (see photos attached).

I really hope that is not the problem with my computer as I don’t think my soldering skills are good enough to recap a power supply…
 

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NightShadowPT said:
My only concern is if the battery I buy online is really new, or just "new old stock", and that being the case it may no longer have any charge.
Do they even make new batteries?
Click to expand...
If it's not being sold as new from a reputable source like Mouser or Digi-Key I would check the date code printed on the module, then do the above mentioned addition of a CR2032 if it's NOS because I'd rather rebuild the one I already have as opposed to buy one and rebuild that in six months.
 
NightShadowPT said:
Maybe I’m missing something, but my power supply seems to be ok (see photos attached).

I really hope that is not the problem with my computer as I don’t think my soldering skills are good enough to recap a power supply…
Click to expand...
Try using a known good or new power supply. They can look like they are working, but the voltages can vary and be unsteady, and can behave oddly like the symptoms you’re having. Use any power supply, even if it doesn’t fit in the case - just use it to test.
 
I have a known good one, its off the thinner prolinea 4/66 but its the same psu. Let me know if you need it. It has low hours and a near silent fan installed.
 
twolazy said:
I have a known good one, its off the thinner prolinea 4/66 but its the same psu. Let me know if you need it. It has low hours and a near silent fan installed.
Click to expand...
Is it the exact same power supply? Mine seems to be purpose built and has a lot of connectors in weird places :)

If they are the same between the Deskpro M series and the Prolinea, that will massively open the possibilities to find a replacement.

If it’s the same, I may take it. Please check your PMs.
 
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