Mainboards can have 6 layers easily, not just the traces on the up- and downside.
So there´s a lot going on "underground".

Old tantalum capacitors (mustard coloured here) love to have short circuits. Then there´s zero Ohms between the supply voltage and ground and the PSU won´t power up.
You have to find the one with the short by desoldering the tantalum caps on the respective supply voltage one by one until you find the culprit.

Hello majestyk and thank you for your answer.

OK, so this is why i lost some tracks...but i think that "underground" tracks have no reasons to die (except huge scratches) ?

Ok, tantalum capacitors are those strange bubbles...i begin to check one of them because right now, even still connected to the board, it is short so it should be on the 12V track ?
Can i try to start the board without one of these capacitors ?
If I find the culprit, do I have to replace it with another tantalum one ?

Thanks !

Ok...so on the +12V track i found this capacitor

Unsoldered, it is shorted ! Seems to be the culprit
Now, to read the value...
is 106 meaning 10 * 10^6 pF? so 10µF ?
is 25V or is the "K" meaning something ?

Can i replace it with another type of capacitor ?

Thanks for your help !

I think you can try your board without tantalum caps.
I've done this myself before and never had an issue

One missing cap will not cause problems, especially on 12V which those boards usually don't use for anything but integrated COM ports.

Thanks for all your answers !

I replaced the capacitor with another "classic" one with same values from an old broken motherboard.
And guess what ???....

Thank you for your help, and thank you majestyk for pointing the tantalum capacitors, it was an huge help and a huge amount of time saved !

Thank you VOGONS community ! 😀

If someone else runs into the same problem, here was the broken capacitor :

Hope others tantalum capacitors on the board won't die...something like 20 on the board !

I think this is your board http://www.win3x.org/uh19/motherboard/show/4288

Would you like to send us a good quality image so we can add it to the page ? 😀

You might want to do a full recap on your board indeed and if not using tantalums make sure you use low-ESR electrolytic capacitors as that is what is mandatory on motherboards.

Hello Deksor ! Yes, it's this one !
Isn't the image in the first post good enough ? My phone is from 2009 and i can't do more thant 5 mpixels. But if you want something more detailed (SLOT, Socket...), please ask ! 😀

Hello evasive. Ok, how can i identify low-ESR capacitors ? the one i have used was from a jetway socket 478 mainboard.

It's not the resolution, it's the light and the angle 😀 (actually I can work with images that have an angle like this but they tend to get blurry and lighting tends to be bad. It's the case for both here)

What I tend to do is to put the motherboard on a piece of paper on a table in a room with exterior light coming and then try to shoot the picture with my phone above it while trying to hold it parallel to the motherboard.

Using your phone's flashlight or putting a bright light source above the mobo is a bad idea and will cause lots of glare.

Ok Deksor, I will try to do this this week end and will post here the picture.
Do I have to remove CPU and memory ?

I have a 486 LPX motherboard that i wasn't able to find in your database nor browsing google (look quite the same as the FIC 486-VA?).
I will take a picture too.

parhelia512 wrote on 2020-12-11, 12:11:

Hello evasive. Ok, how can i identify low-ESR capacitors ? the one i have used was from a jetway socket 478 mainboard.

Recycling from another motherboard is perfectly fine. Just make sure to stay away from the known bad brand capacitors.

Hello Deksor,

Here are the pictures of the QDI + unknown 486-VIA motherboard.
Hope the quality will be good enough for you

Thanks evasive for the advice !

The qdi photo is top !

The other one is a bit blurry but I could identify it 😀
http://www.win3x.org/uh19/motherboard/show/2396

I think there isn't enough light as it's a cloudy day !

Yes, it looks really like this FIC but i do not have that much jumpers near the video chipset nor the same connectors on the I/O shield.
I have 2 PS/2 connectors and on your scheme it doesn't look like PS/2 slot ? Am I wrong ?

Your database is GREAT !

My board BIOS is an Award one.
I have no jumper to change system bus speed, I need to replace the crystal oscillator for bus modification.
Maybe it's a rebranded FIC ? On the board I have what seems to be Hyunday stickers (same on the floppy, hard drive, power supply)...Sadly I don't have the original case 😒

The connectors may not physically look the same, but it's just a mistake/lazyness on Microhouse's side. If you look what these connectors are doing, they're what you expect (CN6 is VGA, the "at keyboard connector" is just the keyboard's connector, etc)

However you're correct about the video jumpers not matching. Moreover in the jumper manual there's "86C805" mentioned which tells us it's using a S3 video chip. Yours is using a cirrus logic.
Maybe that's why your board says "486-VA" and this one says "486-VAL".
They must be close relatives. Maybe evasive has more infos about this one ?

Not on this particular board but I know there is the 486-vac-v which is also LPX, has onboard CL video as well but a different layout. I'll have another dive at the archives and I will add have added that one to UH19 as well.
https://www.ultimateretro.net/en/motherboards/6898

I was operating at "D" for adding chipsets, otherwise I might have seen this one sooner.