Okay, I hooked up a know good tested AT power supply with -5v rail too.
I put in a new CPU Intel dx-33 and checked all my jumper settings.
Now I have some readings on the PC diagnostic reader.
Still NO video however.
I only have a video card hooked up and two sticks of 16mb FPM ram. Which is all the 30-pin ram I have on hand.
What does this error code mean ?

FF-- the motherboard has begun or has finished POSTing but does it changes or does it indefinitely stays on FF?

If it stays on FF without doing anything, then it is likely that the BIOS might be bricked, try with the second BIOS.

Vynix wrote:

FF-- the motherboard has begun or has finished POSTing but does it changes or does it indefinitely stays on FF?

If it stays on FF without doing anything, then it is likely that the BIOS might be bricked, try with the second BIOS.

Yes, it stays on “FF—“
It does not display anything else and the red LED’s stay on. They do not blink.

Does it also hangs on FF on the 2nd BIOS as well? If anything, check also if everything is plugged correctly (and that the CPU is correctly oriented). Then next up would be the CPU and/or the RAM which could potentially be faulty.

(I can somewhat relate, I'm also trying to tackle a similar issue but with a waaaay newer mobo (an Asus M2N-MX) mine does not fire up at all if certain RAM sticks are in)

It only has one bios. A setting to enable bios and a setting to flash the bios.
If I switch settings it does the same.

I will double check the CPU orientation.
I tried different ram and nothing changed.

Would this motherboard post if I removed the Dallas real time clock ?
Or is it needed in order to post ?

Does anyone know where I can get a ROM for this BIOS string ?
AMIBIOS ID string 40-0700-006259-00101111-111192-SYMP-F
40-2800-006259-00111111-121593-SYM WAG-H: Young Micro VS486G-3VL-6B

It's probably needed to POST.

Have you tried to start the board WITHOUT the POST card ? Some motherboards don't really like POST cards when you want them to start up.

That could be also a possible cause that the Dallas is wreaking havoc (if it's flat as a pancake, I'd expect the mobo to fire up yet complain that CMOS settings were lost, the usual stuff y'know?) but it's still worth a try to see if it'll boot with the Dallas chip removed (although I never owned a mobo ancient enough to have a Dallas RTC chip on it). EDIT: As @Deksor said, it's most likely needed to boot...

Another possibility would be that something is shorting the mobo (and in that case, a good way to see that is pulling the mobo out of the case and trying it while it is outside the case, if it fires up outside the case and not inside...)

Vynix wrote:

That could be also a possible cause that the Dallas is wreaking havoc (if it's flat as a pancake, I'd expect the mobo to fire up yet complain that CMOS settings were lost, the usual stuff y'know?) but it's still worth a try to see if it'll boot with the Dallas chip removed (although I never owned a mobo ancient enough to have a Dallas RTC chip on it). EDIT: As @Deksor said, it's most likely needed to boot...

Another possibility would be that something is shorting the mobo (and in that case, a good way to see that is pulling the mobo out of the case and trying it while it is outside the case, if it fires up outside the case and not inside...)

I have the motherboard out of the case and on anti-static material.

Well the fact that the dallas chip contains not only the battery, but also the RTC chip and the nvram makes me think that the system would be very unhappy if it can't find any of this. But to be really sure, someone should try that on known good boards and look what happens ^^

I removed the dallas battery and received the same error code.
So maybe the dallas battery is the wrong type ?
It is good because I checked it with a multi-meter.
But some of the legs are missing by design.

Also, I have tried 3 motherboards already and one is brand new and I get the same problems.
No video.
I have tried 3 graphics cards.
I think I might be using the wrong type of 30-pin ram ? ( 60ns, 30-pin, FPM, 16mb sticks ).
But that is all the 30-pin ram I have on hand.
If I remove the ram the motherboard should still post right ?
I only have connected the keyboard, ram, and video card.

I know the power supply is good and display and video card and keyboard.

I think the ram type is wrong. I will have to get some more ram to trouble shoot further.

I have some good and bad news. I am making progress.
I now have one good working 486 VLB motherboard.
Turns out I had a bad ISA graphics card and a bad CPU.
At least I hope it is the CPU that was bad because I put in a lower speed CPU in a 486dx-66
It worked and posted fine.

As for the other two 486 motherboards they only take 30-pin SIMMs.
And I only have Non-parity FPM SIMMs.
I think I need Party FPM SIMMs.
So I will have to order some.
Also I need to double check these CPU's and Graphics cards and eliminate the bad ones.
Also I need to order some more Dallas batteries and find the right one for this motherboard.

So this posts is going on hold until I receive the NEW components.

Okay, now that I have a working 486dx-66 VLB computer I can test my cards.
So far they are all good but one ISA video card.
So now I have known good working cards.

The problem I am having is with CPU’s ( 486dx4-100 ) they don’t seem to work in my good motherboard.
The manual reads it does support the dx4 and has jumper setting for it. But when I install them
The computer will not posts.
Works fine with 486dx-33, dx50, and dx66 at 5v.

The computer just won’t work with 3v dx4 CPU’s.
I have dx4-75 and dx4-100 CPU’s. Many and they cant all be bad.
So something must be wrong with the motherboard settings manual.

What do you think ?

So far at this point it may be safe to assume that either the new mobo's manual is wrong (a misprint is a rare occurrence but can happen or simply it's the wrong manual) or that the DX4 cpus are bad (they didn't operate on 5V and required a adapter for certain 486 mobos that couldn't supply 3.3V) but yet a bad cpu is rare (it can happen too but it's rare)..

Does the Vega mobo boots up if a 5V cpu is present? (e.g. 486DX-50...)

Another common factor here is all the CPUs that don't work are 3.3V (some are 3.45V actually but both types should work fine with either voltage).
So perhaps these mobos have voltage regulator issues (it's dead or not jumpered correctly).

To check that I'd look for a cheap DX2 that 3V, Intel made some of these as well. If not Intel then AMD but I would stay away from Cyrix/TI. Not that there's anything wrong with them but in general Cyrix requires different jumper setting and proper mobo support.

One more thing, 3V CPUs from Intel (and AMD) are usually Write-Back capable and I'm not actually sure what would happen if the mobo doesn't support WB (only WT) and also perhaps doesn't signal that properly to the CPU.

What is this motherboard setting acronyms ( P24D ) ?
I don’t know what these acronyms stand for in CPU settings options ?

Here is the error code i get from the 486dx-100 cpu.

P24D is a code for later 486DX2 and DX4 series CPU that had write-back cache. And those are pretty much always 3V so maybe that's the problem. I don't know what that code is, but it's pretty low number so good chances are it's cache related as it's checked very early in the boot sequence. Plus the fact that you do get codes at all means the CPU is not completly dead and so the voltage regulator should also be OK (although maybe it's unstable or just about to die).

YES !
It is working at 486dx4 100mhz !

I have some questions
What is P24D WT#
And. P24D WB

These P24D setting where the problem.
But I don’t know if I have it right yet because I don’t understand what these acronyms stand for ?

Thanks in advanced.

P24D is not an acronym but a code name for Intel 486 CPUs that had clock multiplier and write-back cache. Your mobo most likely predates the launch of DX4 series so they've only had the code name to go with.
WB stands for Write-Back, and WT for Write-Through cache. For Intel DX4 CPU you should set your motherboard for P24D WB. Unless it's a 5V Overdrive to 100MHz. Then you set it up like it was a 5V DX-33 (so that you could actually install it in mobo that didn't support any DX4 CPUs).

Okay, thanks. I checked all my 486dx4 CPU’s and they work fine.
So in all that I only found one ISA video card that did not work.
I now have a box of good tested cards to complete my “All-USA-486” build.

Now I have to wait for the new ram and Dallas clock to arrive.

Okay, I am still trying to get this Young-Micro 486 motherboard to work.
I compared with another working motherboard of the same type.
So my jumpers are set correctly.

The problems could be the Dallas clock or Bios chip.
Currently It will NOT post.
The CPU does not get hot.
No beeps , Nothing.
Only the keyboard lights blink on first power on.
PC diagnostic reader repost nothing, No error codes.

I have a question.
I have several other working 486 motherboards
Can I take the bios chip out of one of them and test in this motherboard ?
They do have a different chipset however.
Some are Contaq and SIS and Intel.
My NON-working motherboard has a Symphony chipset.