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Compaq Portable 486c

T

twconstantine

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Joined
May 3, 2024
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I managed to pick up three of these awesome computers in hopes to make one 100% version. Looks like I have my work cut out for me! I’ve never recapped a PSU, but all three are shot. I’m sending out two of them to a wonderful human that is going to recap them for me. I’d like to try and tackle the third so I can learn.
After that I hope it’s pretty straightforward. I know some people managed to get an AMD 586 as a drop in upgrade. Also I’ve heard the CF card is hard to get working in this. I hope that’s not the case since all three are missing hard drives. I also think I need a CD drive, but looks like it needs to be external.
Please let me know your thoughts on this and what I should consider!
 

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ajacocks said:
That's some determination!

I have a 486c, as well, with the common dead screen. I'm in the process of replacing the screen with a modern replacement.

- Alex
Click to expand...
Just in case you're not aware, if dead means "all white" this can be fixed by replacing most of the caps on the back of TFT panel. I've fixed mine that way, though I didn't manage to replace all caps (some are really hard do reach for desoldering).
 
mikerofone said:
Just in case you're not aware, if dead means "all white" this can be fixed by replacing most of the caps on the back of TFT panel. I've fixed mine that way, though I didn't manage to replace all caps (some are really hard do reach for desoldering).
Click to expand...
Thank you! Thats good to know. I need to rebuild my keyboard cable since my only one has fallen to pieces.
 
In my case, the screen is physically broken. Thanks for letting me know about the capacitors, though.

I haven't replaced or upgraded anything else, yet. I want to fix the screen first.

- Alex
 
Didn't some of the Compaq Portables have expansion units that attached to the back, with one of them being a CD-ROM? Would that be applicable to this late model, or was that only for the earlier models?
 
Paralel said:
Didn't some of the Compaq Portables have expansion units that attached to the back, with one of them being a CD-ROM? Would that be applicable to this late model, or was that only for the earlier models?
Click to expand...
There is a port on the back that I don’t recognize. My Compaq portable 386 has an expansion pack that connects to the back. Maybe this model does too? Not sure.
 
Anyone have any ideas on how to get a 486c? I just missed 2 listings on eBay literally by hours. They get bought up so fast. Hopefully it's not somebody trying to scalp them.
 
If you do manage to find one, don't be dumb and try and immediately power it on. The PSUs in those things are a dangerous mess.

I worked on two for another member here earlier this year and they were electrolyte bombed to hell. Managed to get one of them working again, the other had I believe a blown up power IC that is near unobtanium. There's a design fault where said IC is fractions of an inch from rectified mains, and the leaked electrolyte can result in a bridge forming from +370v to a low voltage trace and things just get worse from there.

Due to the narrow nature of the PSU, Compaq had to compromise on safety to have such a low profile design.
 
GiGaBiTe said:
If you do manage to find one, don't be dumb and try and immediately power it on. The PSUs in those things are a dangerous mess.

I worked on two for another member here earlier this year and they were electrolyte bombed to hell. Managed to get one of them working again, the other had I believe a blown up power IC that is near unobtanium. There's a design fault where said IC is fractions of an inch from rectified mains, and the leaked electrolyte can result in a bridge forming from +370v to a low voltage trace and things just get worse from there.

Due to the narrow nature of the PSU, Compaq had to compromise on safety to have such a low profile design.
Click to expand...

I'll keep that in mind, I already knew that it was from capacitor plague era, but I didn't know how bad it would be. Recapping a PSU shouldn't be too bad, but hopefully what you say won't happen when I eventually find one. I recapped a Mac classic II and it wasn't too hard, but replacing ICs is a pain in the ass, especially when you have to replace ones soldered on flex cable like the plasma screens in a PIII. I'm currently doing that now. I thought it would be impossible to find stock of the line driver chips for the plasma screens so I opted to ask around on the forum, and I got a few screens to canabalize and I'm going to send one working one back. I kept searching the deepest pots of the Internet and just recently a few days ago, I found potential suppliers for all four ICs and I'm ordering them now. I'll make a guide on fixing these screens when I'm done, because every video I found on fixing them are fringe videos that are hard to find.

I'm still looking for a 486c, if anyone wants to sell/giveaway thiers I'll take it, I keep checking eBay and every time one shows up (if it ever shows up) I missed it by a few hours. WHICH HAPPENED TWICE. Anyway I desperately want one, but I also don't want to go into debt trying to sink my teeth into one. I am a college student and money is tight, but I still know not to be unreasonable. I won't low ball for an unopened new old stock CP 486C, because I don't have the money for that. Plus I love doing the work on broken machines anyway.
 
CompaqSniffer said:
I'll keep that in mind, I already knew that it was from capacitor plague era, but I didn't know how bad it would be. Recapping a PSU shouldn't be too bad, but hopefully what you say won't happen when I eventually find one.
Click to expand...

Oh, recapping the PSU will be an absolute nightmare. Be prepared for 4-8 hour sessions over multiple days. You'll need to remove the daughterboards and mosfets and clean the entire board within an inch of its life with solvents, soap and water to get rid of the electrolyte. You'll also need to remove the transformers and clean them, because electrolyte will wick up their legs and start eating the copper windings. There's also a large copper shunt that needs to be cleaned.

You'll probably have to end up replacing diodes, ceramic caps, resistors and other parts due to the nature of the electrolyte. It can wick inside those components and corrode them from the inside out. Don't just clean and recap, you'll need to test every single component on the board. This is important, because if electrolyte is shorting something internally, or creating phantom bridges, it can blow up and take all of the money and work with it. And don't forget to replace the power switch. If the spades on the back of the switch are discolored, like blue, the switch is damaged and needs to be replaced. I would do it anyway because the contacts can arc and carbonize and cause enough of a voltage drop to cause problems.

I have a partial parts list of components on the power supply somewhere. If I can find it, I can post it if you need it.
 
My Portable 486 was working but started flaking out and smelling like fish after it ran for two full days at a retro fair. Contrary to GiGaBiTe's experience, fixing that only required replacing the caps and cleaning up under a few of them, as the electrolyte leakage was small and only happened for those tiny caps at the bottom of the PSU which are encased in heatshrink. In case you might find it useful, my notes (for a 220V PSU in case they are not multivoltage, don't remember) are in this Google Sheet: https://docs.google.com/spreadsheets/d/1dDGA_tNauIGRGyKVHcXrOHezk4TOOm9lcnAxqPL2UvQ/edit?usp=sharing
Note that I didn't change the two large ones, as replacements were expensive and they looked and measured perfectly fine.

Sounds like a thorough visual inspection is the first order of business if you get one, and if you don't see electrolyte everywhere, it might be a quick repair. Good luck!

Cheers
mikerofone
 
Hey I managed to actually find one, what kind of keyboard does a 486c use? is it rubber domes or mechanical? also does it have the standard cherry cross switch thingy? I'm asking because I should have one on the way to me, and I wanted to know if it was possible to customize the keyboard.
 
It's a rubber dome keyboard that hasn't anything particular going for it, aside from it having shallower travel than regular desktop keyboards.

I've popped a key and this is what it looks like:
portable486_keyboard.jpg

Hope that helps!

Cheers
mikerofone
 
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