Tiido wrote on 2024-12-02, 19:27:

If the riser board isn't having 12V on it, the card isn't going to output anything even if it does work in another system. You can see ISA pinout here and can verify that all the voltages are present : https://en.wikipedia.org/wiki/File:ISA_Bus_pins.png

5V is definitely present or the card wouldn't be doing anything at all, but it will need 12V to power its analog stages and lack of sound output points to the likelyhood that 12V is missing.

Hehehe! I was looking at the same pinout diagram... Thanks! So, I'll start by measuring voltage on ISA slots from the riser card. I was hoping to isolate the riser from the equation...

BINGO! Nothing on the 12V rail...... Now I need to figure out where it drops along the way... Unless there is a better solution?

**UPDATE**

I GOT IT!!! There was ANOTHER burnt trace under the board that was coming right from the main 12v power supply connector! So f'ing happy!!

Now, I have to figure a way to have my "aftermarket" PSU fit into that custom Compaq case and external plastic bezel... But that's the least of my worries!

Very nice ~

There shouldn't be much getting in the way of using a different PSU since the screw holes etc. are all in the standard locations. I did have to remove the AC output connector when I was fitting a different PSU into my machine from same series years ago. Care must also be taken to make sure the power switch is wired correctly, if not it'll produce a loud bang which will destroy the switch in the process.

The problem is more fitting the rear cover with fan and power connector at a precise location...

The fan, connectors and screwholes are still in exactly same place as they are on any regular power supply, compaq didn't use anything out of standard on this machine. Only thing that will get in the way is a power output connector if present, since there is no cutout for it in the plastic or the metal frame, but if you take it out from the PSU it'll fit and all the exposed screwholes fit too.

The PSU does rely on two screws on opposite end for proper mechanical stability, that not all PSUs have bracket for, although many have holes to attach such a bracket and you could perhaps steal in from the original PSU if it is removable. It was on my original compaq PSU, which I now use as PSU for my arcade stuff since it is a very high quality one with overcurrent protections and all ~
Other option is to simply move the insides of the PSUs around, nearly all of them have the screw holes etc. in exactly same locations so it isn't difficult to swap around the PCBs. You do have to pay attention to the two big capacitors on the primary side, they will be able to bite very hard (potentially lethally) if not discharged.

Exactly what I am doing! Since nothing's easy, I noticed two slightly bulged caps while doing the transplant... Waiting on replacement caps to arrive. To top it off, the replacement psu had a small pcb attached to the power connector. With its new position in the Compaq's psu case, the main pcb is in the way! I'll need to move it somewhere else in the psu. Ugh!

I started searching for a plan B on classified ads and found a PC Power & Cooling Silencer 275W. Perfectly aligned with the rear cover and even had the bracket at the bottom! However, I noticed a bulged cap... Darn. I figured I would just fire up a few minutes to see if it works fine. Well, not at all!! Keyboard keys were all wrong and it would not initiate the sound card... I quickly turned it off.

I checked the voltage of the 12v rail and gave 10v... 3.3v rails gave me 2.5v. Yuk! So I guess my plan B will also need so work...

Careful with the prolinea.
They use custom pinouts on the psu

You might be able to revive the existing one with new components, but be careful with the caps. I believe the standard is to short them before working on them.
Put the board on a piece of aluminium foil when removed should work.

myne wrote on 2024-12-05, 04:49:

Careful with the prolinea. They use custom pinouts on the psu […]
Show full quote

Careful with the prolinea.
They use custom pinouts on the psu

You might be able to revive the existing one with new components, but be careful with the caps. I believe the standard is to short them before working on them.
Put the board on a piece of aluminium foil when removed should work.

Not really! At least not on a 4/50... I used a good ol' ATX to AT PSU adapter and everything standard.

I didn't want to take any chance and totally scrapped the original one (the insides) since it was revving (on-off-on-off...) when re-testing it and that fried 12v trace makes me believe it was the PSU's fault...

Transplant completed! I had to stick that little PCB at the back of the casing to be safe... Since it's a little too loud for my taste, I will give a good try at fixing that Silencer 275 PSU. But getting 10v on the 12v rail sounds like a problem deeper than just replacing that bulged 3300uf 10V capacitor...

Aside from that, everything has been reassembled and the computer is in a working condition! With few little things that will need improvements:

Top ISA slot: with a sound card there, it still makes the computer go in wacko mode... The keyboard caracters get mixed up and SetupSA hangs the computer. I am thinking of desoldering that ISA slot from the riser to place the CF card adapter there and make enough room to install a wavetable on that (very low) Audician32.

Missing SMT capacitor: there is still that missing cap beside the onboard RAM... I haven't had any random crashes, all memory tests were successful and increasing to 16MB of total RAM wasn't a problem. So think I will leave it as is instead of risking a fix that could break something else.

Almost all capacitors on a circuit are decoupling caps to dump the high frequency noise/reflections to ground.

It's wrong to call them redundant, but...

Usually things continue working fine without them.
There might be a measurable increase in emi though.

Think of them as the dampeners (shock absorbers) on a cars suspension.

Without them, the springs go wild, and the wheel can bounce off the road on bad terrain, but it will still drive.

Fortunately, there are usually many decoupling caps, so losing one or 2 almost always has zero effect noticeable to the user.

myne wrote on 2024-12-07, 15:25:

Almost all capacitors on a circuit are decoupling caps to dump the high frequency noise/reflections to ground. […]
Show full quote

Almost all capacitors on a circuit are decoupling caps to dump the high frequency noise/reflections to ground.

It's wrong to call them redundant, but...

Usually things continue working fine without them.
There might be a measurable increase in emi though.

Think of them as the dampeners (shock absorbers) on a cars suspension.

Without them, the springs go wild, and the wheel can bounce off the road on bad terrain, but it will still drive.

Fortunately, there are usually many decoupling caps, so losing one or 2 almost always has zero effect noticeable to the user.

Exactly what I thought... There are 2 caps still installed beside an unpopulated ram space. I guess using those would make sense then...