Now, I don't know if I need to do a new thread for this...

But since the seller of the Compaq KVM authorized me in opening the unit, I noticed that the faulty PSU is connected to the PCBs with two connectors that looks pretty similar to 4pin ATX ones. One has four cables coming out of it, the other just two, even if it's still 4 pin.

What do you think? Are they actually 4pin ATX connectors, and should I try connecting a new ATX PSU to it and see if the PCB is still alive, and it wasn't fried when the original PSU blew?
I'm not that familiar with PSUs and connectors, so I don't know if the voltages from a 4pin ATX PSU would be good for this.

That depends on what order the wires go in, and what voltages are on them. I would think they carry 5V primarly and maybe 12V. I can see different wire colors but a photo of the PSU itself will help more than just the connectors themselves. But I'm pretty sure you're not gonna be able to use an ATX PSU here, not as is. But it is most likely possible to fix the PSU it has and it is definitely possible to adapt something else into it too but both of those will require some knowledge, supplies and equipment. It would be nice to see photos of the rest also.

Tiido wrote on 2025-02-23, 18:29:

That depends on what order the wires go in, and what voltages are on them. I would think they carry 5V primarly and maybe 12V. I can see different wire colors but a photo of the PSU itself will help more than just the connectors themselves. But I'm pretty sure you're not gonna be able to use an ATX PSU here, not as is. But it is most likely possible to fix the PSU it has and it is definitely possible to adapt something else into it too but both of those will require some knowledge, supplies and equipment. It would be nice to see photos of the rest also.

I have all of them here.
Yeah, they kinda looked like 4pin ATX, but of course I also thing it's can't be as easy as plugging in an ATX PSU and call it a day. The fact is... I would like to know if the PCB didn't fry itself before spending money on it. Because I sure won't connect this PSU into a wall socket again.
(you can see the nice black stain on the top side of the case, right where the PSU is).

EDIT: replaced pictures with higher resolution ones.

The photos are too low resolution to really tell anything (720 x 960 is not a lot especially if they are not closeups).

I would expect one of the primary side filter capacitors to have gone poof but I cannot really tell at all. I'm unable to see any obvious source of the problem at the resolution the images have. The grey rectangle in highlighted area would have been my first suspect, perhaps it has a bulged side etc. The smoke in video did look like a capacitor had given up but none of the electrolythic ones appear to have vented. But I think I see tantalum capacitors on the main boards, plenty of them, and those do have a tendency to short and do what was seen in the video...

The PSU is definitely outputting 3 kinds of voltages, 5V and probably 12V and perhaps -12V for some of the analog bits but without measurements you cannot be completely sure.

Did the KVM stop working and then you unplugged it, or you unplugged it before it could stop functioning ?

In any case you'll want to scrutinise all the boards visually to see any signs of a rupture etc. on any component or perhaps a bad trace somewhere, since a shorted tantalum can make those burn up and it will also produce smoke like seen in the video.

Tiido wrote on 2025-02-24, 00:35:

The photos are too low resolution to really tell anything (720 x 960 is not a lot especially if they are not closeups). […]
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The photos are too low resolution to really tell anything (720 x 960 is not a lot especially if they are not closeups).

I would expect one of the primary side filter capacitors to have gone poof but I cannot really tell at all. I'm unable to see any obvious source of the problem at the resolution the images have. The grey rectangle in highlighted area would have been my first suspect, perhaps it has a bulged side etc. The smoke in video did look like a capacitor had given up but none of the electrolythic ones appear to have vented. But I think I see tantalum capacitors on the main boards, plenty of them, and those do have a tendency to short and do what was seen in the video...

The PSU is definitely outputting 3 kinds of voltages, 5V and probably 12V and perhaps -12V for some of the analog bits but without measurements you cannot be completely sure.

Did the KVM stop working and then you unplugged it, or you unplugged it before it could stop functioning ?

In any case you'll want to scrutinise all the boards visually to see any signs of a rupture etc. on any component or perhaps a bad trace somewhere, since a shorted tantalum can make those burn up and it will also produce smoke like seen in the video.

In the evening I'll get better and closer pictures.

I don't actually know if it stopped working. The second I heard that noise I started inspecting the rear of my setup and, when smelled burning, I just pulled out everything from the wall socket. I didn't know yet it was the KVM.
Visually I didn't saw any damaged capacitor. But the smell comes from the PSU, not the board itself.

Ok ~

I forgot about the image where I referenced the "grey rectangle in highlighted area"

But ok, I'll wait for the closeups etc.

Mondodimotori wrote on 2025-02-21, 18:31:

Well, got myself a Compaq KVM and it arrived today. Payid less than 30€ with all cables and shipping. Following the manual, I co […]
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dionb wrote on 2025-02-07, 18:01:

I used to have a Compaq KVM, it was really good, although the controls were a bit of a pain (used smartkey instead of buttons, when you powered it up, it gave you a GUI...). Check the manual for the model for how it works and see if that would be OK for you.

And why decent quality? Because Compaq also made high-end graphical workstations, and because they regularly over-engineered a lot of stuff like this. Beige Compaq generally (leaving out awful Presarios) meant solid quality. And again, in this era people who wanted quality (and were prepared to pay the then premium for Compaq's professional line) also used VGA.

Well, got myself a Compaq KVM and it arrived today. Payid less than 30€ with all cables and shipping.
Following the manual, I connect the unit and, glory, it works and, after booting the PC, it even looks good! Then I hear a noise.

Then I smell burning.

OH GOD.

I rush to disconnect everything from power and... I see smoke coming out of the KVM.

They warned me about old PSUs... They warned me about old capacitors on old MOBOs... No one ever warned me against KMVs, 🤣.

Just a short video of the aftermath (may be NSFW for some people sensible to old tech smoking)

PS: Luckly no PCs or Monitors were harmed in testing the unit.

Argh!

Sounds exactly as expected - except for the magic smoke 😦

What do you think? Are they actually 4pin ATX connectors, and should I try connecting a new ATX PSU to it and see if the PCB is still alive, and it wasn't fried when the original PSU blew?
I'm not that familiar with PSUs and connectors, so I don't know if the voltages from a 4pin ATX PSU would be good for this.

A connector shape in no way guarantees that the pinout will be compatible; Compaq had some very incompatible 20p PSU pinouts with the same connector as ATX in the very period this came from. Don't assume it will be the same!

That said, the idea of putting a more modern PSU in there to deliver the same voltages to the system board makes a lot of sense - I've done similar mods before (most memorably: powering a Roland MIDI patchbay direct from +5V USB instead of via a big heavy transformer which needed 110V input)

Looking at the colours, I see yellow, red, white and black. If those are standard, that would be +12V, +5V, -5V and GND. I'd be pretty confident about the yellow and red, but white needs more checking of components on the PSU board.

Tiido wrote on 2025-02-24, 00:35:

The photos are too low resolution to really tell anything (720 x 960 is not a lot especially if they are not closeups).

Got ya covered. I inspected the capacitors on the PCB. They are teeny tiny and in good health. No bulging or leaking.

dionb wrote on 2025-02-24, 12:01:

Argh! […]
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Argh!

Sounds exactly as expected - except for the magic smoke 😦

A connector shape in no way guarantees that the pinout will be compatible; Compaq had some very incompatible 20p PSU pinouts with the same connector as ATX in the very period this came from. Don't assume it will be the same!

That said, the idea of putting a more modern PSU in there to deliver the same voltages to the system board makes a lot of sense - I've done similar mods before (most memorably: powering a Roland MIDI patchbay direct from +5V USB instead of via a big heavy transformer which needed 110V input)

Looking at the colours, I see yellow, red, white and black. If those are standard, that would be +12V, +5V, -5V and GND. I'd be pretty confident about the yellow and red, but white needs more checking of components on the PSU board.

Yeah, I have a couple of options if I can't try it with another PSU: Either spend a little bit more in another Compaq KVM I found on the same webside (different seller), or get one of those desk avocent I found on ebay. Only they come without cables and power brick. The cables I'm trying to keep those from the Compaq, hoping the seller will agree to a partial refund without needing to return anything (more for the fire scare than else), the power brick will be an addition to the final bill.

About the PSU that died, here's higher resolution pics I took with a Reflex. I hope they are clear enough. I would really love to, at least, test if the PCB is still alive and working, and that the PSU failing didn't kill it. That's why I would like to understand if a common ATX PSU can provide the correct voltages and power to it.
Also I really don't want to open the unit further unless it's to try a fix. The burnt smell that comes from the PSU is still pretty strong the second I open it. If I can't find a suitable PSU, I'll just keep the unit but will get rid of that stinky PSU.

(Pictures of the connectors on the PCB should be good alredy in the previous post)

These are a lot better. I had to adjust gamma to see into the dark parts aaaand nothing stands out. Maybe there's a burned trace underneath the PCB... This much smoke must have left a mark you can't miss...

Tiido wrote on 2025-02-24, 22:26:

These are a lot better. I had to adjust gamma to see into the dark parts aaaand nothing stands out. Maybe there's a burned trace underneath the PCB... This much smoke must have left a mark you can't miss...

Well... It did left a mark, and you can see it in a photo in a previous post.

Mondodimotori wrote on 2025-02-23, 19:06:

(you can see the nice black stain on the top side of the case, right where the PSU is).

The attachment kvmaperto1.jpg is no longer available

It's on the case, right on top of the PSU. That's why I excluded any failures on the mainboards. But something blew on the PSU, and I don't think I can remove it from the KVM while I still have an open case with the seller. He may actually decide to give me a full refund and wanting the unit back, even if I told him I'm open o keep it for just a partial refund (those cables are indeed pretty nice and usefull). So I won't be able to take a picture of the PSU on all sides, outside the KVM.

(sorry for the low gamma, it was dark and I didn't have a stronger flashlight than the one on the phone).

The stuff above PSU also happens during normal operation and accumulates over time, so it isn't a 100% sure indication that anything is wrong there. The PSU gets relatively hot and causes air motions, and because of high enough voltage it is able to electrostatically attract dust and soot (especially when people smoke) from the air and it often deposits on the surfaces nearby (and in the PSU circuits), leaving marks similar to that even when nothing goes wrong. This is seen inside nearly every CRT monitor and AT(X) PSU.

Tiido wrote on 2025-02-25, 20:20:

The stuff above PSU also happens during normal operation and accumulates over time, so it isn't a 100% sure indication that anything is wrong there. The PSU gets relatively hot and causes air motions, and because of high enough voltage it is able to electrostatically attract dust and soot (especially when people smoke) from the air and it often deposits on the surfaces nearby (and in the PSU circuits), leaving marks similar to that even when nothing goes wrong. This is seen inside nearly every CRT monitor and AT(X) PSU.

So... If it may not be the PSU itself that blew (even if the burnt smells comes from it), should I try and connect it to power again? Maybe while keeping it open to visually check if there are problems?

If you dare, that will definitely reveal the culprit. Some precautions should be done, such as doing it in a place where there isn't anything potentially flamamble, such as a bathroom floor. If a tantalum explodes there will be hot smouldering bits flying around and it isn't nice when one such ends up in a carpet or a couch etc.

This did remind me of a fault I had with one old 286 computer, and the problem ended up being the power supply transformer itself. It had a shorted turn in it and began smoking as soon as power was applied while at the same time everything else looked unharmed. It did stink of burned electronics too and it might be the case here too... and if it is, there's no recovery unfortunately.

Tiido wrote on 2025-02-26, 12:53:

If you dare, that will definitely reveal the culprit. Some precautions should be done, such as doing it in a place where there isn't anything potentially flamamble, such as a bathroom floor. If a tantalum explodes there will be hot smouldering bits flying around and it isn't nice when one such ends up in a carpet or a couch etc.

This did remind me of a fault I had with one old 286 computer, and the problem ended up being the power supply transformer itself. It had a shorted turn in it and began smoking as soon as power was applied while at the same time everything else looked unharmed. It did stink of burned electronics too and it might be the case here too... and if it is, there's no recovery unfortunately.

Yeah... I don't have a fire extinguisher yet, but I had alredy planned to get a CO2 one for the whole retro PC setup.
I actually don't care that much in recovering the PSU, but only if it could be possible to use another ATX PSU with it and check if the PCB didn't die.

It will definitely be possible to adapt another PSU for it, but it will help a lot to actually determine what the voltages, either by direct measurement or inferring from what the PSU uses and what components are powered and what they expect.

Belkin Omni View SE works perfect for me:

https://www.youtube.com/watch?v=zpbbA1DNelg

Tiido wrote on 2025-02-26, 13:10:

It will definitely be possible to adapt another PSU for it, but it will help a lot to actually determine what the voltages, either by direct measurement or inferring from what the PSU uses and what components are powered and what they expect.

Guess I'll have to get me a multimeter.
Only... How do you test voltages if the unit is smokey? Or firey?

MAZter wrote on 2025-02-26, 13:17:

Belkin Omni View SE works perfect for me:

https://www.youtube.com/watch?v=zpbbA1DNelg

Added it to the list!

It may be a small fault that can be fixed without too much trouble, but it may come down to detective work where you analyze the PSU connections and what it connects to in the main boards. It is most likely it has +5V, +12V and perhaps -5V or -12V for analog parts. In many PSUs the negative voltage is made with a linear regulator and just looking at the part number tells exactly what that voltage will have to be.

Tiido wrote on 2025-02-27, 00:47:

It may be a small fault that can be fixed without too much trouble, but it may come down to detective work where you analyze the PSU connections and what it connects to in the main boards. It is most likely it has +5V, +12V and perhaps -5V or -12V for analog parts. In many PSUs the negative voltage is made with a linear regulator and just looking at the part number tells exactly what that voltage will have to be.

Well, the seller never came back to me (weird) with a response, and the platform just issued a full refund, without needing to return the unit.
At this point I may very well find someone to look at it, that's more well versed in electronics. Maybe some lab that works with servers may have the necessary expertise. If it's not too expensive, I'll do it. Otherwise I can use this thing to tinker and learn how to do it myself.

If I still lived in Estonia I could be an option, but now I'm in Norway and since it is not in EU there's all the extra taxes and postal service here is totally insanely expensive too...

But photos of the PCB and knowing of part numbers can go a long way in that detective work I mentioned. But there's still need for someone to actually solder stuff eventually (or at least adapt the wiring).