Deksor wrote on 2021-07-16, 08:23:

Maybe a picopsu would do the trick ?

I've not tried, but I'd imagine the 5v rail is nowhere near powerful enough.

OKay guys today i've tried out with the PWR_OK solded in.

THere is some change, now when i start the PSU everything starts, the HDD etc. And there is some white stripes poping and disapearring at the very beginning. Is it normal to this?

From this :

To this : (and after the screen is going black and nothing happends)

Here is the video for you to see :

https://www.youtube.com/watch?v=idIJ1V6ihik

Verax wrote on 2021-07-15, 17:26:

And also, how do i do to start the PSU? Do i need to bridge two wires together like the green one (Which is PS_On) with another one?

You can start the ATX PSU by connecting PS_ON signal to GND (preferably the one right next to it). I've used (un)bent paper clip for that purpose, and found it's easier (and maybe even safer) to have that connection made semi-permanently and actually powering on/off via a switch on the AC side. Connecting the bare wire to powered system, as you are doing, is just asking for trouble.

I think people greatly overestimate 5V power draw on these older machines, sure it's significant but if you limit yourself to one floopy drive and perhaps no mechanical HDDs (or just one) then the rest (mobo+cards) will draw maybe a couple amps total. This it not a Pentium system where some 15W go into CPU alone. After all you only have 2 pins dedicated to 5V on that mobo connector.

It looks like the voltages match the standard colors (red=5V, black=GND, etc) so that leaves only the brown wire. Perhaps this is a PWR_GOOD signal and the negative voltage you see there is a measurement error or some weirdness of the mobo. Certainly there is no need to have two -5V inputs.
Try connecting the brown wire to 5V but not directly but via 100ohm resistor. And not by hand either, solder this connection in place. This will protect the mobo and PSU in case it's a wrong assumption - the resistor might get very hot (shouldn't relly start smoking though). If that doesn't work, try with white wire but I would expect this one to be -5V which you can leave unconnected for now, it's rarely used. I'd be very surprised if mobo needed it to run (but some sound and graphics cards might need it).

As I said, my PCS 11 (same motherboard as the PCS 33) will happily boot without the -5v rail, and the pinout I posted is correct.

Verax: I'd be tempted to try an ISA video card, just in case the issue is now with your onboard video.

Deunan wrote on 2021-07-16, 10:42:

You can start the ATX PSU by connecting PS_ON signal to GND (preferably the one right next to it). I've used (un)bent paper clip […]
Show full quote

Verax wrote on 2021-07-15, 17:26:

And also, how do i do to start the PSU? Do i need to bridge two wires together like the green one (Which is PS_On) with another one?

You can start the ATX PSU by connecting PS_ON signal to GND (preferably the one right next to it). I've used (un)bent paper clip for that purpose, and found it's easier (and maybe even safer) to have that connection made semi-permanently and actually powering on/off via a switch on the AC side. Connecting the bare wire to powered system, as you are doing, is just asking for trouble.

I think people greatly overestimate 5V power draw on these older machines, sure it's significant but if you limit yourself to one floopy drive and perhaps no mechanical HDDs (or just one) then the rest (mobo+cards) will draw maybe a couple amps total. This it not a Pentium system where some 15W go into CPU alone. After all you only have 2 pins dedicated to 5V on that mobo connector.

It looks like the voltages match the standard colors (red=5V, black=GND, etc) so that leaves only the brown wire. Perhaps this is a PWR_GOOD signal and the negative voltage you see there is a measurement error or some weirdness of the mobo. Certainly there is no need to have two -5V inputs.
Try connecting the brown wire to 5V but not directly but via 100ohm resistor. And not by hand either, solder this connection in place. This will protect the mobo and PSU in case it's a wrong assumption - the resistor might get very hot (shouldn't relly start smoking though). If that doesn't work, try with white wire but I would expect this one to be -5V which you can leave unconnected for now, it's rarely used. I'd be very surprised if mobo needed it to run (but some sound and graphics cards might need it).

Thanks for your message! THat's a lot of informations for me to digest haha, but i'll see what i can do with my (poor) competence in electronics 😁
I've connected the green wire to the black like you said i didn't find it "healthy" to start the machine with a flying wire, so now i start automatically when i turn on the PSU on the back. 😀

I've disconnected the hard drive as well, so now there is only the mother board and the screen, nothing else, i've tested like this and it didn't change much sadly.

I don't know if i'll try your last solution because i'm a little bit inexperimented with voltage, watts and stuffs like this, i don't want to kill myself or kill the board. haha

Also what do you call the "mobo"? (Sorry i'm not native English)

paradigital wrote on 2021-07-16, 12:03:

As I said, my PCS 11 (same motherboard as the PCS 33) will happily boot without the -5v rail, and the pinout I posted is correct.

Verax: I'd be tempted to try an ISA video card, just in case the issue is now with your onboard video.

Yes i think that everything is correct because it starts out so i think it is something else now that the PSU is out of the problem equation?

So you say the onboard video chip should be faulty? Is it possible to change it?

Anything is possible to replace with the right equipment. It might not be the video chip that's failed, it could be the video DRAM, it could be a corroded trace, anything. But in order to rule it out, try an ISA video card. You'll likely want one anyway, as the onboard video isn't the greatest. I had to install my Tseng ET4000AX in order to run games like Commander Keen.

Does the keyboard show signs of life when the PC is powered on (do the lights for CAPS, Scroll or Numlock do anything)? Do you get any audible beeps from the onboard speaker? If the answer to both of those is no then it's still likely to have a mainboard problem.

paradigital wrote on 2021-07-16, 12:21:

Anything is possible to replace with the right equipment. It might not be the video chip that's failed, it could be the video DRAM, it could be a corroded trace, anything. But in order to rule it out, try an ISA video card. You'll likely want one anyway, as the onboard video isn't the greatest. I had to install my Tseng ET4000AX in order to run games like Commander Keen.

Does the keyboard show signs of life when the PC is powered on (do the lights for CAPS, Scroll or Numlock do anything)? Do you get any audible beeps from the onboard speaker? If the answer to both of those is no then it's still likely to have a mainboard problem.

Yes i agree, but it's hard to find especially from a newbie like me. ^^

I don't have any ISA card, should i buy one to try it out? Which model do you recommand for this PC ? 😀

For the keyboard, all green lights stay ON "NUM" "CAPS LOCK" etc. but nothing happends so far.

No bips from the onboad speaker, no posts whatsoever. 😒

I'm actually changing some caps, then i'll restest everything and get back to you!

The fact that the keyboard stays lit up suggests that the PC isn't POSTing properly, regardless of the display working or not. The keyboard should be initialized (flash all three LEDs once), and if the test is successfully passed the PC moves onto testing the Floppy and Fixed Disks (you would see the floppy seek at this point). If the keyboard isn't initialized properly then the PC would beep at this point and pause on a keyboard error.

There's definitely something not right with the mainboard, assuming the power rails are now all correct.

Looking back at your pictures, your BIOS chip doesn't look like it's seated properly either, though does look seated enough to make contact with all pins. I wonder if it's been removed before.

So here it is, i changed all major component on the mother board, and it still the same nothing happends, so maybe the video chip is dead?

I'm looking for an ISA video card then. 😀

https://youtu.be/hfZwXCUhVr0

paradigital wrote on 2021-07-16, 13:58:

The fact that the keyboard stays lit up suggests that the PC isn't POSTing properly, regardless of the display working or not. The keyboard should be initialized (flash all three LEDs once), and if the test is successfully passed the PC moves onto testing the Floppy and Fixed Disks (you would see the floppy seek at this point). If the keyboard isn't initialized properly then the PC would beep at this point and pause on a keyboard error.

There's definitely something not right with the mainboard, assuming the power rails are now all correct.

Looking back at your pictures, your BIOS chip doesn't look like it's seated properly either, though does look seated enough to make contact with all pins. I wonder if it's been removed before.

Hmm okay that's strange then. So yes that's "normal" for the PC not to boot if the POST isn't passing on the keyboard. What could be the cause of that? i have no clue.

Yes now it's definitly the mother board.
What do you mean "Seated properly"? Do i have to take it back and look if i can put it correctly?

Has keyboard been plugged in every time you tried it? Just because a bad keyboard should be ruled out. Try without, if it then gets as far as complaining about not having a keyboard, then the keyboard must have problems.

BitWrangler wrote on 2021-07-16, 18:32:

Has keyboard been plugged in every time you tried it? Just because a bad keyboard should be ruled out. Try without, if it then gets as far as complaining about not having a keyboard, then the keyboard must have problems.

Nope most of the time i didn't plugged the keyboard in. I've try with and without. I also tried with another Compaq keyboard, and the same thing happends, all green lights keep showing and never stop until i stop the PSU. That's really strange!

I think it’s worth getting hold of a POST test card, they are only €9 or so on Amazon and will tell you if the voltage rails are good on the ISA slots, as well as show you if any POST messages are actually happening.

paradigital wrote on 2021-07-16, 07:01:

Oh I've successfully booted my PCS 11 with an ATX PSU before with the pinout I described above. As my ATX PSU was newer than the ATX 1.x specifications it didn't have a -5v rail, so I left that out (P22).

I did this months ago mind you. I knocked up an adapter using a filed down du-pont connector for the end that plugs into the PC, and a female ATX connector to plug into the PSU.

I'm pretty confident that my issue is going to be finding a PSU that fits inside the small form factor of the PCS 11. So far I'm coming up short, even most 1U rackmount PSUs are too long 🙁

If you still have the old power supply you should try to change these two capacitors, which are on the feedback line of the power supply , same time solve the problem of death PSU

If it doesn't work you can replace the power supply with this one, I normally use it with 286,386 ,486 and same pentium motherboards

Obviously with a suitable power supply, I will shortly do it on my pcs11 and let you know

dataino.it wrote on 2021-07-16, 19:29:

paradigital wrote on 2021-07-16, 07:01:

Oh I've successfully booted my PCS 11 with an ATX PSU before with the pinout I described above. As my ATX PSU was newer than the ATX 1.x specifications it didn't have a -5v rail, so I left that out (P22).

I did this months ago mind you. I knocked up an adapter using a filed down du-pont connector for the end that plugs into the PC, and a female ATX connector to plug into the PSU.

I'm pretty confident that my issue is going to be finding a PSU that fits inside the small form factor of the PCS 11. So far I'm coming up short, even most 1U rackmount PSUs are too long 🙁

If you still have the old power supply you should try to change these two capacitors, which are on the feedback line of the power supply , same time solve the problem of death PSU

Is this message for me or @paradigital ?

dataino.it wrote on 2021-07-16, 19:37:

If it doesn't work you can replace the power supply with this one, I normally use it with 286,386 ,486 and same pentium motherboards

Obviously with a suitable power supply, I will shortly do it on my pcs11 and let you know

Okay, but i'm already using a brand new PSU with the PC. 😀 Thanks it can be useful though!

Verax wrote on 2021-07-16, 19:50:

Okay, but i'm already using a brand new PSU with the PC. 😀 Thanks it can be useful though!

This might be a silly question, but did you try pressing the reset button? This is especially important if you do a resistor mod in place of proper PWR_GOOD signal from PSU, like I suggested earlier. My 286 mobo doesn't always properly boot after power-on, I suspect the PWR_GOOD timing is not in spec sometimes on my old AT PSU, or the mobo expects even longer delay than the mandated 100ms to properly reset itself. This is where a manual reset a few seconds after power is applied can help.

Also, re-seat the BIOS ROM chip. It looks kinda crooked on the photos, might not be making good contact on all pins.

Deunan wrote on 2021-07-16, 20:13:

Verax wrote on 2021-07-16, 19:50:

Okay, but i'm already using a brand new PSU with the PC. 😀 Thanks it can be useful though!

This might be a silly question, but did you try pressing the reset button? This is especially important if you do a resistor mod in place of proper PWR_GOOD signal from PSU, like I suggested earlier. My 286 mobo doesn't always properly boot after power-on, I suspect the PWR_GOOD timing is not in spec sometimes on my old AT PSU, or the mobo expects even longer delay than the mandated 100ms to properly reset itself. This is where a manual reset a few seconds after power is applied can help.

Also, re-seat the BIOS ROM chip. It looks kinda crooked on the photos, might not be making good contact on all pins.

This PC is really special in terms of buttons and all, but i'm using a new PSU and so i'm not sure how to do the "reset" thing manually? Could you tell me please? Is there a wire i have to bridge with another?

Sorry again i'm a beginner, but how do you take of the CPU for this model? I know how to do it on modern PC'S but this one looks different?

Thanks for your help though!