POST cards are good for nothing in XTs (that's what I learned recently 😀 ). I would start with swapping BIOS ROM with Supersoft Landmark Diagnostic ROM - but for this to work you will need MDA or CGA card (it won't work on VGA). There's also Ruud's diagnostic rom but I prefer Landmark's one.
http://www.minuszerodegrees.net/supersoft_lan … dmark%20ROM.htm

Ah, that is kinda annoying as I only have one compatible CRT ... Oh well I'll try that, thanks a lot ! (Actually SOME vga card might work apparently)

Have you tried swopping out the RAM chips in bank 0 with those in bank 1? Take note that, since you have a 256-640KB revision of the 5160 motherboard, you can only swop RAM chips between bank 0 & bank 1.
A failure of any of the chips in bank 0 results in what appears to be a 'dead' motherboard - more info here: http://www.minuszerodegrees.net/5160/problems … #bank_0_failure
I can also highly recommend this site for further information and the forums on http://www.vcfed.org, particularly this section: http://www.vcfed.org/forum/forumdisplay.php?2 … -PCs-and-Clones.

Hopefully, your problems are not as severe as my one motherboard, which had some RAM delay line issue (I never managed to resolve the problem completely).

Well ...

It works flawlessly ... (floppy read is showing an error because I didn't plug any floppy drive)

It seems like that board acts dead if I use my VGA card (which I've tested on a 8 bit ISA slot), but with MDA it's perfectly fine !

Problem solved I belive ? (Thanks again for your help 😁)

Well ... like I mentionned, I have two boards, the other one still acts dead (nothing happens even on the POST card), no beeps, nothing with the landmark ROM, nothing with the BIOS.
I may have a clue though, I think that the fan spins quite fast with that one, so there may be some more bad caps in there (on the +5V I think)

Deksor wrote:

By the way, there is some life in that board : when I put my POST card in it, I see the numbers moving really fast (I think it's an incrementing value. It's really going too fast to read anything, but I think I see the pattern of a hex number being incremented), then it stops on "0F" shortly, then it countinues, and then it stops on "0F" again, and this time it's stays there forever.

.

Already mentioned this in HanJammers XT repair thread, but thats exactly what I observe on my (working) XT-boards. So at least you can see something is going on.

To my surprise, when you send data to port 80h on an XT with debug.exe, it is not displayed on the POST-card. This works on 286 up. Dont have an explanation for this yet...

Nice monitor btw 😉

Thanks, but unfortunately it's not working very well, the picture itself is ok, but the colors are brighter on the left than on the right and they fade to the right. And R, G, B aren't affected the same. They're all affected, but red seems to be the most affected color.

I have no idea what does this nor how could-I fix that.

Is there a change in focus left-to-right, or just the brightness?

Hard to say since things tend to be more blurry on crts when it's too bright. But I'd say (though I'm not sure) that this is the brightness.

Likely not a HV issue then. Although any CRT monitor repair should start with re-soldering each and every pin on the flyback transformer.

If geometry looks OK-ish then it's probably a capacitor issue somewhere in the cathode drivers. Shorts and weak tubes typically have a single color going missing or the whole picture brightness is affected. Replace all electrolytic capacitors on the neck board, if that doesn't help, the main board as well. Don't skip the low value ones (1-10uF or so), these too dry out and cause all kinds of problems.

Deksor wrote:

It seems like that board acts dead if I use my VGA card (which I've tested on a 8 bit ISA slot), but with MDA it's perfectly fin […]
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It seems like that board acts dead if I use my VGA card (which I've tested on a 8 bit ISA slot), but with MDA it's perfectly fine !

Problem solved I belive ? (Thanks again for your help 😁)

Well ... like I mentionned, I have two boards, the other one still acts dead (nothing happens even on the POST card), no beeps, nothing with the landmark ROM, nothing with the BIOS.
I may have a clue though, I think that the fan spins quite fast with that one, so there may be some more bad caps in there (on the +5V I think)

It may be BIOS related. My XT motherboard (not the one from the repair thread) worked fine with VGA and dip switches set to 'mono' monitor. Anyway unless you want it to be 100% original I would replace the BIOS with Super PC / Turbo XT BIOS which adds plenty of "modern" features like boot from HDD and support for HD floppies (even the 2,88MB ones).
Grab it here: http://www.phatcode.net/downloads.php?id=101

Probably it will also fix the VGA issue (also if this VGA is 16-bit make sure it works in 8-bit mode - on Trident cards you will have jumpers for that).