Just got a Compaq Portable (1) with power problems...

[DistantStar001]

I got a Compaq Portable and it won't turn on. The fan goes, but that's about it. I began by removing all the ISA cards, but no luck. Then I unplugged the power to the floppy drives and tested for shorts between ground and the power lines. All toned out. So then I removed the motherboard. The 12v line seemed fine, but the 5v was short. Even so, I gave it a power test. So I reconnected one of the drives for load, and the heater on the CRT lit up on power-up. I checked the voltages, and the 5v and 12v lines read perfect...

I was unable to find a schematic or manual online (at least not a good manual), so I used the pinouts from the ISA slots to check for shorts between the powerlines and ground. All three of the cards I want to retain and found no shorts (there was a 20MB hard card in there, but the odds of the drive working are slim, and an SD or CF to ISA adapter isn't that expensive so I'll probably ditch it). The motherboard on the other hand is shorted between 5v, 12v, and ground. So I started checking the capacitors. C48, C77, and C78 all tested short in circuit. As did R4 and R22, but they could be connected to other components. C83 tested open. Unfortunately, none of these components appear to be marked. So if anyone could tell me what I need for the recap, it would be appreciated.

Side Question: I'm about 99% certain I should erase this, but then, I've heard some argue for the preservation of markings from the original owners... However, in this case, the original owner in question put his full name, state driver's license, and social security numbers on the inside case. There were also some stickers as well, but they were falling off anyway. I'm all for preserving history, but this is a bit more info than I was expecting. Any thoughts?

 

[dracalion]

Hello, I have a couple compaq portable motherboards and I can get you the specs for those caps. Im currently away from home however so I cant tell you until later today.

there are two versions of the portable's motherboard that I know of, and I have one of each. does your board have one or two sets of dip switches?

 

[booboo]

I would start by replacing the tantalum capacitors on the +12V on the motherboard, adjacent to the power connector from the PS. Those were sorted on my system. You'll also find (or will in time) shorted tantalums (again on 12V) on the video card and the floppy/serial ISA card. I've yet to see any shorts on the floppy drives. Check archive.org, you'll find service manuals there.

Oh, and the system fan always works as it's on the 120V AC side.

 

[dhau]

there are two versions of the portable's motherboard that I know of, and I have one of each. does your board have one or two sets of dip switches?

If you don't mind, please share high quality photos of each version. I have two Compaq Portables, and they both have the same motherboard.

 

[dracalion]

C48, C77, and C78 all tested short in circuit. As did R4 and R22, but they could be connected to other components. C83 tested open. Unfortunately, none of these components appear to be marked. So if anyone could tell me what I need for the recap, it would be appreciated.

C48 and C78 are marked 473 for 0.047uf at 16 volts
C77 and C83 are marked 106 for 10uf at 16 volts
R4 is marked 510 Ohms with 5% tolerance
R22 is marked 33 Ohms with 5% tolerance, I notice its a bit larger then a normal resistor

If you don't mind, please share high quality photos of each version. I have two Compaq Portables, and they both have the same motherboard.

upon further inspection they actually seem to use the same board layout, with the only difference being a couple ROM sockets not soldered in and the lack of the 2nd dip switch block, my apologies.

here are pictures of both boards:

 

[DistantStar001]

Hello, I have a couple compaq portable motherboards and I can get you the specs for those caps. Im currently away from home however so I cant tell you until later today.

Looking forward to it! I may have found some, but not all. Also, given the age of this, I might want to to a total recap to prevent further failures.

there are two versions of the portable's motherboard that I know of, and I have one of each. does your board have one or two sets of dip switches?

The board I hvae has only one set of switches.

I would start by replacing the tantalum capacitors on the +12V on the motherboard, adjacent to the power connector from the PS. Those were sorted on my system. You'll also find (or will in time) shorted tantalums (again on 12V) on the video card and the floppy/serial ISA card. I've yet to see any shorts on the floppy drives. Check archive.org, you'll find service manuals there.

That's the plan. So far the ISA cards seem alright, but I'll likely recap them as well. Side note, it looks like the 5v rail is shorted as well. So I'll have to figure out what's causing that. As for the service manual, that turned out to be a bit harder than a simple search, as the results I got were for the Portables 2, 3, and 386, along with some laptop manuals. I did eventually find the Sam's Gude. But I had to turn to Google to get it (link below):

Manual: 101709PORTABLE SM COMPAQ EN : Free Download, Borrow, and Streaming : Internet Archive

Manual: 101709PORTABLE SM COMPAQ EN

archive.org

As you can see, the name on the file isn't exactly search friendly. Unfortunately, as helpful as this is, the parts list isn't comprehensive, and the shematic is a little vague. Of the capacitors that tested bad, only C48, C77, and C83 are listed. leaving C78 a complete mystery. Moreover, C48 is listed as part of the power supply when the one I'm lookingh at is on the system board...

If there is a better or clearer guide or manual out there, then maybe you could post the links?

 

[DistantStar001]

C48 and C78 are marked 473 for 0.047uf at 16 volts
C77 and C83 are marked 106 for 10uf at 16 volts
R4 is marked 510 Ohms with 5% tolerance
R22 is marked 33 Ohms with 5% tolerance, I notice its a bit larger then a normal resistor

just saw this. THANK YOU!!!

upon further inspection they actually seem to use the same board layout, with the only difference being a couple ROM sockets not soldered in and the lack of the 2nd dip switch block, my apologies.

Yeah... But that second one is identical to my board. So helpful nonetheless. Also, it makes me wonder what the purpose of that second set of switches was. Could it have something to do with the number of ROMs? Maybe a revision consolidated the code to a single ROM and rendered the second set redundant? Or do the second ROM and dip switches offer some expanded capabilities?

In any case, a bit of an update: On the grounds that C77 was the easiest to get to, I removed it and now no longer have any shorts on the ISA slots (other than pins 1 and 10 which are both ground). I also removed and tested R4 and R22. R22 still tones out on a continuity test but the screen read 33 something when it did, and the ohms reading was 32.5. So I'll assume that it's fine and my meter isn't sensitive enough on continuity not to tone out at 33 Ohms. In any case, I put it back. R4 on the other hand, reads 27 Ohms and also tones out on continuity. So I'm pretty sure that's bad.

So two questions: 1) Is C77 necessary for normal operation? and 2) Can I assume that all the orange balloon-shaped capacitors that look just like it have the same values? Because after 39 years, I think it's time for some replacements!

 

[booboo]

Yes, the later release of the ROM rendered the 2nd bank of switches unused. SW 2 is only used if you have less than the 640KB on board with older ROM. ROM C can autodetect memory.




Board revision 2 included the C ROM and therefore switch bank 2 was removed. If C ROM is on Board revision 1, then switch bank 1 is ignored.

 

[modem7]

If C ROM is on Board revision 1, then switch bank 1 is ignored.

... and switch bank 2 (SW2) is treated as though it is switch bank (SW1). Just thought I would clarify that to readers.

 

[dhau]

here are pictures of both boards:
View attachment 1257604

I am pretty sure you only need one BIOS chip in top socket. Somehow you got two! I'm positive it's safe to remove the second ROM chip, may be use it on another board. As it is right now, I think you have two copied of BIOS starting at different addresses.

Also, U35 is empty, is it because you did the 640K onboard mod and you got a GAL chip on a DIY PCB going into that socket? Like this one: https://monotech.fwscart.com/Compaq_Portable_640K_U35_RAM_Decoder_PROM/p6083514_19805777.aspx

 

[dracalion]

I am pretty sure you only need one BIOS chip in top socket. Somehow you got two! I'm positive it's safe to remove the second ROM chip, may be use it on another board. As it is right now, I think you have two copied of BIOS starting at different addresses.

I always did wonder why it had 2 BIOS ROMs... it never caused issues so I didnt worry about it that much. That board in paticular was upgraded from a "portable" to a "portable plus" by a shop in the 80s which also included a 10 meg hard drive in the chassis. why they put 2 ROMs in beats me

 

[dracalion]

Also, U35 is empty, is it because you did the 640K onboard mod and you got a GAL chip on a DIY PCB going into that socket? Like this one:

I completely forgot to reply to the second half of your post. Yes I did upgrade the u35 PROM, in fact the product linked is the exact one Im using. I removed it for the board photos since the PCB obscures some stuff

 

[DistantStar001]

Update!!! IT BOOTS!!! I still can't do anything with it as the keyboard is non-responsive. But that was to be expected with a foam/foil. I've already ordered some replacements from Texelec, so I'll have to deal with that when they arrive. Also, the RAM expansion card (a SixPakPlus card) appears to have an intermittent fault on it. When installed, sometimes the machine will boot, and sometimes it won't. Could be the battery? Could be something else. BUT!!! For now (at least with the minimum of cards), it's powering up reliably, and loading from a floppy!

As for the original problem... From what I can tell, C77 was the only failed component. Also, R4 on my board was a 30 Ohm, not 510 Ohm. Which is why it was toning out on my meter. However, that may be a board revision as there is a jumper wire connected to U14 that runs to the nearest resister pack. Even so, I replaced it just to be safe.

I DO intend to do a full recap of at least the tantalum capacitors, but I'm not so sure I want to mess with a working power supply. Personally, I've always been of the "if it ain't broke" mindset.

Beyond that, I'm planning to get a CF or SD card adaptor, as well as a serial joystick adaptor, and then start loading it up with some games!

 

[booboo]

Generally I've only seen the 12V tantalums fail on the Compaq and IBM motherboards, so I wouldn't necessarily change those on 5V lines.

 

[modem7]

Also, the RAM expansion card (a SixPakPlus card) appears to have an intermittent fault on it. When installed, sometimes the machine will boot, and sometimes it won't. Could be the battery?

I doubt it, but obviously, removing the battery is a test.

Something simple to start with would be to do a good clean of the edge connector fingers on the card. And to try the card in a different slot (in case of a slot specific problem).

BTW. In case you are unaware, note the information in the 'Portable and Portable Plus - Powering off then on' link at [here].

 

[DistantStar001]

I doubt it, but obviously, removing the battery is a test.

Removed it. Seems to work now. So either the battery was the problem, or it just magically decided to work now. Honestly, wouldn't be the first time. As I have a couple of Apple II PSUs that gave me nothing but problems for years. Clicking, ticking, no voltage... Then one day, they just decided to work, and have been reliable ever since. I swear, I didn't do anything to them! I hate it when that happens. You never know if or when it's going to fail. And as long as it's working, there's no way to trace the potential fault.

Also, I tested the Hard Card. And... It's dead. No big loss.

In any case, I think I've taken this thing as far as I can until the replacement pads arrive for the keyboard.

 

[dracalion]

Also, the RAM expansion card (a SixPakPlus card) appears to have an intermittent fault on it. When installed, sometimes the machine will boot, and sometimes it won't.

My sixpak plus has a similar problem. With the RAM expansion part of it enabled, the machine its installed in refuses to boot. All the other functions of the card appear to work. I dont need that part anyway since I installed Monotech's decoder PROM replacement so i can put the full 640k on the motherboard

try flipping the dip switches to turn off the RAM expansion part and see if it works

 

[DistantStar001]

I WAS WRONG!!! Sorta... I really can't say if the SixPackPlus is faulty or not. But I can say that my Portible PSU is cutting out after extended use. Looks to be about twenty minutes or so. About ten to fifteen with the SixPack installed. I guess this means I really will have to recap the PSU after all.

Still... Progress. The machine boots, the keyboard now works, and the flopy drives read and boot disks!

 

[dhau]

Check this blog port: https://oldcrap.org/2020/10/08/compaq-portable/
Section: Replacing Compaq Portable Power Supply

 

[dracalion]

Check this blog port: https://oldcrap.org/2020/10/08/compaq-portable/
Section: Replacing Compaq Portable Power Supply

just like there are two motherboard revisions, there are multiple power supply revisions too. except unlike the motherboard, the PSU revisions are very different from each other. if @DistantStar001 has the new revision motherboard, they may have the new revision PSU too which is not featured on that blog post. If they need specification readings for specific components I will be happy to help, as I have both PSU revisions (and they both work!!)