Well, for one, the power supply has had it 🙁 I have a whole parts MACHINE, thankfully -- short of drives and the slidey inner part of the drive cage that the drives actually mount to...

I'll swap the rest of the system over, I think, and test it there.

Bummer ! Those Compaq's are very nice.

Rebuild the irreplaceable Compaq PSU is mandatory by experienced. Spares is non-existent, 286e and 386e ditto to Deskpro M, and any n models, the ones with 2 slots and one 3.5" floppy used on 286n and 386ZS also have PSU plugged directly into 2 slot riser in turn sends juice to the motherboard.

Also any early Deskpros with PSU that is part of chassis.

Cheers,

I'm about to pop the lid off my parts-machine PSU to see what I'll be facing. Any good guides out there? I've not googled but I'm generally pretty horrible at google.

I'm pretty sure I shouldn't use this power supply!

YIKES!!

Nothing else looks bad tho -- no visibly bad caps or anything. But that is one KFC Extra Crispy resistor!

Guides or advice/suggestions *plz*?

I have an electronics background, I can do this, but I'm not experienced specifically with power supplies. I have several multimeters and a dedicated (cheap tho) continuity tester. I also have a *very* old oscilloscope, but it dates from the mid-1960s (no joke, look it up, it's a Tektronix 422), and although I have all the literature for it, the manual that tells me how to use it references equipment I *don't* have and can't afford -- like a signal generator -- so that's perhaps best left in the closet for now. I don't think it'll be of much use here anyways.

Somewhere I also have one of those "multi component testers" with the single button and the LCD but I don't think it'll help much here either.

The rest of that power supply looks perfectly fine. I'll try and post photos of both of 'em -- not just the one blown resistor in the spare -- in the next few days. A pity the wires aren't labeled internally; it's complicated enough that reverse engineering is going to be a real bear if it's genuinely necessary.

As an aside, I have a supply from a Toshiba T3100e laptop in the closet -- I know its HV+/- output is fairly similar (for the plasma panel) -- close to spec although not exactly perfect. I was told explicitly that the laptop it came from was good only for parts, if that, but I may see if I can test the supply on its own. My main concern there will be that the +12v rail on *that* supply is good only for 1.1a instead of 3a... it should, however, self-regulate without a minimum load, although I'll test it with a drive of one sort or another attached just to be safe... probably a 5.25in floppy or older optical drive, I have a few laying around 🤣. If it tests out, I may see if I can shoehorn it in somehow... I may try to relocate the display card to the former power supply bay, because I'll never use the Compaq proprietary expansion cards, and I'm pretty sure the T3100e power supply will fit quite nicely across the expansion and display card bays if I remove the dividers between them... sure it's a bit of Frankensteining, but it gets the job done and it's at least period parts 🤣.

"I am going to bahmp yoo aaahp!"

Your old scope should be fine for checking for ripple, it's either gonna be in the 50/60 Hz AC range or in the 10s of Khz range from the PSU conversion switching.

I don't even know enough to do that with it 🙁

But I'm gonna need help diagnosing the rest anyhow. Again -- any guides out there? Failing that, anyone willing to guide me here?

Buy a ESR capacitor meter. The switching power supply can be serviced but need to substitute the components as original parts were no longer made. Toughest part is blown resistors means you need to look into working power supply of exact one.

Study the power supply of compaq's to understand what they work.

Cheers,

I have a "multi component tester" (like this -- https://i.imgur.com/1nNmZ2d.jpg ) but I don't have anything that works in-circuit (unless those do? I actually don't know) and I'm really awful at desoldering. Multiple rework cycles is going to be a very bad thing here TBH.

What's worse is that Compaq uses some sort of slimline 5.25in floppy drive I've never seen anywhere else -- maybe that's me, 🤣 -- and at least one variety pulls enough power (up to 1.5a) that the Toshiba supply isn't an option with that one. I have two of those -- Okidata GD3305BU, with a springloaded flap on the front that conceals the disk insertion slot. I have another Compaq (a Portable II that doesn't work and is not going to be restored, because "I don't want to talk about it!") that has a different kind of drive in it (it had one of each). I think the other drive is a 360k drive but I don't remember. I'll go look in a while -- it's in a closet in another room, and kind of a pain to get to within that closet.

Kind of annoying that regular 5.25in drives don't fit...

One of these 240W ATX SFF PSU from HP would work perfect, pull apart to get board and install that, just add a -5V regulator if needed.

Cheers,

Ridiculous as it may seem, I'd like to at least *try* to keep the electronics somewhat period for now.

"What is this?"
"It's your father's thread-bump. This is the method of an OP. Not as clumsy or as random as a troll, but an elegant device for a more civilized age."

My other 5.25in slim drive (AAARGH @ Compaq 🤣) is a Canon MD5501 slim variant.

Anyone have power consumption data on that? I can't find squat -- really in terms of *any* documentation, even for the standard-height version.

These photos show the spare Compaq PSU. I have more that I'll attach shortly.

For a couple of good (well, to me!) reasons, I'm not likely to bother with the other supply.

One, you pretty well have to strip the body and chassis down to the level of a kit of parts and fasteners... seriously, you have to deconstruct the entire chassis to get the PSU out! It was a royal pain on the one machine that was already mostly disassembled... I'd really prefer to avoid doing it a second time and then some on the nearly fully *assembled* box.

Two, I'm in the midst of trying to configure the BIOS -- which is where this all started -- and I've reached a point where I'd honestly rather replace the chips with ones I have from another system that not only has a ROM-resident BIOS Setup, it's one that autoconfigures everything but hard drives! Since I've heard that almost all PC/AT-class machines have interchangeable BIOSes, I'm hoping I can make this work. I *will* try and boot with the old BIOS before swapping chips, simply to avoid introducing additional problems for myself ahead of time, 🤣 -- I just know it will fail to boot with the old chips.

Three, the intent with the drives was always to run one hard drive and one 1.44mb 3.5in floppy drive. While I somewhat agree with the purists, right now I don't have a simple way of creating 5.25in floppy disks -- or 720k 3.5in disks, for that matter -- and limiting myself to such drives would *severely* hamper the utility of the system. This machine was meant to be used, after all, and I want to honor that.

So I think my next steps are to (1) try and source a few replacement PLCC 286 CPUs, (2) try and work out the pinout of the old PSU, (3) make an adapter cable to allow the Toshiba T3100e PSU to connect to the Compaq motherboard, and (4) try and get it booting with the new PSU and a better BIOS.

At this point, the best help I could get is, if anyone knows the motherboard power connector pinout or is willing to suggest ways to suss it out, I'd appreciate it. It's a 13pin connector, marked "P101" on mobo silkscreen. It appears identical to the connector used in early Compaq Deskpro systems, at least from 8086 through 80386 generations; however, this connector appears entirely publicly undocumented from everything I can tell.

All I can work out so far is, pin1 is 0vGND, pin2 is 12v, pin3 is a key pin and is thus missing; working out the rest is quite a challenge because they all shunt to 0vGND until one receives a "power good" signal. Pins 4&5 are common at the mobo, as are Pins 6&7. Pin 8 is brought out alone. Pins9,10,11,12 are common, and Pin13 is brought out alone as well.

If anyone is familiar enough with the old Deskpro systems, the ones with 13pin PSU outputs, to provide their PSU pinout, I'd appreciate it. If anyone happens to know the pinout of *this* system, please share it! and if anyone has suggestions for reverse-engineering the pinout, please share whatever you've got!

These are the additional photos I have of the spare Compaq Portable III supply.

To repeat myself, for the sake of clarity (yes, this is a slightly edited copypasta)...

At this point, the best help I could get is, if anyone knows the motherboard power connector pinout or is willing to suggest ways to reverse-engineer it, I'd appreciate it. It's a 13pin connector, marked "P101" on mobo silkscreen. It appears identical to the connector used in early Compaq Deskpro systems, at least from 8086 through 80386 generations; however, I can find absolutely no documentation regarding pinout.

If anyone is familiar enough with the old Deskpro systems, the ones with matching output connections, to provide their PSU pinout, I'd appreciate it. If anyone happens to simply out-and-out know the pinout of *this* system, please share it! and if you have ideas regarding reverse-engineering the pinout of the supply, I'm interested to hear what you have to say.

Thanks in advance...

A lead on that pinout would be really awesome, guys... anyone?

If you have a Compaq Deskpro with a CPU that's at least an 8088 and no later than a 386, it almost certainly will have that power supply. 13 pins, long gray stiff ribbon cable to a bright orange connector. I know so far that Pin1 is 0v GND. and Pin2 is +12v. The other pins are all shunted to 0vGND at powerup except Pin3 which is missing, it's a key pin so you can't put it in backwards no matter how crosseyed you get 🤣. Anyone who knows or is willing to take a stab at it, I'd really appreciate it.

@pentiumspeed in particular -- you have this thread -- Compaq power supply pinouts archive. (from 8088, 286 and 386, 486, and pentium era ISA and EISA era, UPDATED -- calling for pinouts, but I don't see it mentioned there. Is there any chance that you've got info you somehow haven't had the time to add to that thread that might also help here? (I really doubt my luck's anywhere *remotely* near that good, 🤣 -- but forgive me for checking, please!)