Vipersan wrote on 2021-09-26, 09:34:

As mentioned already I have fitted a coin new cell battery holder and diode to replace the leaky varta so it is delivering 3.2 v to the motherboard.

Remember that in the NiCd age, these weren't often discharged below 1.1V/cell, and there was no real incentive to ensure that oscillators continued to oscillate at low voltages and CMOS SRAMs kept their contents below that threshold.
Try again with a 3x1.5V alkaline replacement, or check out whether there is a protective silicium diode on the board (which itself adds another .6V drop). Either shunt it or replace it with a Schottky type.
If the board keeps the memory after that, you know that it needs more than the 3V of a new CR2032.

retardware wrote on 2021-09-26, 09:43:

Remember that in the NiCd age, these weren't often discharged below 1.1V/cell, and there was no real incentive to ensure that os […]
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Vipersan wrote on 2021-09-26, 09:34:

As mentioned already I have fitted a coin new cell battery holder and diode to replace the leaky varta so it is delivering 3.2 v to the motherboard.

Remember that in the NiCd age, these weren't often discharged below 1.1V/cell, and there was no real incentive to ensure that oscillators continued to oscillate at low voltages and CMOS SRAMs kept their contents below that threshold.
Try again with a 3x1.5V alkaline replacement, or check out whether there is a protective silicium diode on the board (which itself adds another .6V drop). Either shunt it or replace it with a Schottky type.
If the board keeps the memory after that, you know that it needs more than the 3V of a new CR2032.

Thanks buddy ..I'll try that.
Just curious though...where exactly are the changes stored ?
There is a shunt jumper to clear cmos....and the voltage is making it that far....but drops to about 2.56v by that point.
rgds

Vipersan wrote on 2021-09-26, 10:07:

Just curious though...where exactly are the changes stored ?

I don't have a photo, so just search for the chip that connects to the 32,768Hz crystal.

Vipersan wrote on 2021-09-26, 09:34:

There is a shunt jumper to clear cmos....and the voltage is making it that far....but drops to about 2.56v by that point.

This smells of a silicon diode (voltage drop usually .52 to .58V).
On page 22, the board manual explicitly talks about 4.5 or 6V external batteries, so 3V is definitely not sufficient.

Ok ...Ive replace the diode I had in circuit in series with the 2032 ..using a shottky..
The voltage is now acceptable and cmos changes are retained.
So I fitted a PT-606G controller card ...and hooked this to a 1.44mb floppy.
Set in the Award bios to 1.44mb floppy drive A:
please keep in mind I am a relative NEWB to motherboards from this period.
Popped in disk 1 of my DOS6.22 set ...and the floppy starts to boot ...very slowly.
Boot process comes to a halt with.
"Starting MS-DOS"
"Invalid Command.com"
"Insert Disk with \command.com in drive A:"
"Press any key to continue..."
???
I have tried the disk in another PC ..and is fine and boots OK...so whats going on ?
advice appreciated
rgds
VS

Maybe it doesn't read the file correctly (eg, errors, bad checksum)
Bad drive? (Not so rare)
Misaligned or dirty heads leading to read difficulties? (Seems not rare)
Borderline floppy cable? (Rare but I also had such)
Bad power supply? (Not rare, but hard to identify without PSU test bench with configurable loads, voltmeters and oscilloscope)

So I'm starting to wonder if this a BIOS/Cmos issue ...or maybe the controller card ?
I have tested 3 floppy drives on another more modern PC and 3 ribbon cables with the DOS boot disk...
All check out ok ..
All allow booting.
...and yet If I use these in any combination on the GA-486VF I get the same no boot condition.
Perhaps there is a more recent bios I can try ?
rgds
VS

Apparently the name of the last bios file is Vsfbi.ZIP
It has LBA support...but damned if I can find it archived anywhere ?
doh!

There is a page out there that has the download, but I can't find it right now. I have the file though.

BIOS is the same as for the GA-486VS, which is not surprising since the boards are almost identical, except for the SIMM slots.

Thanks for the file buddy..
I will be trying it as soon as I've found me a blank 512 eprom.
cheers

Wrote the eprom but never got a chance to try it..
The mobo no longer boots.
Just switched on from cold ...and nothing ...not a beep.
Checked the psu voltages ..all present and correct.
cpu barely gets warm to the touch.
The only other thing I can and have checked is the pins on what I assume is the regulator that derives cpu running voltage
LT1085CT
A variable voltage regulator..
Input voltage is 5.2v
output middle pin is at 3.4v
This may be a little high but if the cpu isn't running ??
how tollerant are DX 3v cpus ?
The other possiblity is the cmos has died or become corrupt somehow.
This I can check since I dumped it ..and can write a replacement.
I assume that at boot time...only the cpu and bios are important and anything else in the system would be irrelevant until boot is completed ? ...and a shorted component in the system would be warming up ...and nothing is atm.
I am going to lift the keyboard controller which is socketed ...just to see if anything changes.
I cant believe I have gone from such a high to such a low in the space of a few hours.

It has happened before and it will happen again.
Relax, it's probably nothing.

3.4V won't harm the CPU. I think it's safe for 3.3V +/- 0.3V.

Oh, wait up... I noticed that the BIOS identified your DX4-100 as a DX2-100. I had an Award BIOS that misidentified an Am5x86-133 as a DX2-100 and it caused no end of weird problems.
Try finding a different BIOS - and try blanking the CMOS (there's usually a jumper for that, though worst case you'll have to pull the battery and let it sit for several days).

Not found anything obvious at this point...
No beeps with or without simms..
No post codes faulty or otherwise.
I have the post card installed just to check the voltages are present..
All are lit 5v 12v -12v all present ..
The clock led is lit.
but this is curious maybe..
I'm sure the reset led is supposed to flash once at startup...but is permanently lit.
So the cpu held in the wrong state to start up..
clutching at straws now.

You don't live near any embassies do you? 🤣

Not looking good for this one..
I think It likely I may have to give up on this.
The reset pin on the CPU is grid reference C 16 ...and metering continuity mode from C 16 to everything else on the motherboard...the only thing giving a response id the 85C471 chip.
So I'm guessing reset is generated internally here.
Not sure I want to try changing that even if I could get one.
I guess it either just gave up and died or the faulty post card did more damage than I first thought.
I'm not a happy bunny tonight.

No idea what went wrong, but maybe undoing the changes on the board you did today might help?

And maybe check the voltages using a multimeter when board is connected, not only with the port-80 cards' LEDs.
As you probably have no load on +12V on your test rig, it could well be possible that +5V is too low.
On my power supply test bench, I have had power supplies that let +5V drop below 4.2V when only loading +5V. At such voltages, hardware may work randomly, strange/spurious non-replicable errors can appear, like boards not starting at all.

I wonder why exactly did the last successful boot identify the CPU as DX2-100. To my knowledge it doesn't exist at all. Are you not running your bus at 50Mhz?
Do you by any chance have any 5V CPUs to try such as DX-33? The 5V setup may give that case some extra leads

Not totally given up on this yet but is currently being shelved.
I strongly suspect the 85C471 has failed ..and as luck would have it that QPF208 chip is actually available from an ebay seller in Poland.

In the meantime I have returned my attention to the SOYO 4SA2 motherboard I am still having a strange problem with.
It will simply not boot from a 3.5" floppy.
It starts ok ... "starting MS DOS..." then hangs the system with small white flashes on screen. which actually look like a random fast moving cursor.
It is no longer possible to ctrl alt delete reboot at this point.
Pressing this key combo stops the random white flashes to be replaced with a solid flashing cursor line in the middle of the screen.
The only way out is power down.
I was curious if the motherboard could actually boot at all completely ...so installed DOS on a hard drive in another PC ...
Not possible from the setup as is.
Transfered the hard drive to the SOYO ...removed the bootable floppy ...and watched as it booted to DOS.
The next curiosity was ...insert DOS installation disk 1 in the floppy drive...change from C: to A: and DIR..
The entire directory scrolls on the screen.
So the SOYO can see the floppy contents ...but can't boot from it.
Can anyone explain that ?

Whatever this strange fault is ..it relates to running anything directly from Floppy it would seem.
I have a copy of CHECKIT on 2 x 5 1/4 inch floppies and bizarre things happen when I run checkit from the disk...however If I make a directory on the C drive and copy the 2 disks contents across checkit runs just fine fron C
I currently have it checking the system and memory...
So far everything passed.

So I guess it's not a deal breaker for this mobo..
I can at least use it and build a system.
Providing I install DOS on a different computer to a hard drive ..then attach that hard drive to this motherboard..
I can then install windows 3.11 from floppys onto that hard drive ...
I just can't boot anything using a floppy drive on the SOYO.
I would love to know why that is...but I may never find out.
Probably the most curious fault I have ever had.
If anyone can make sense of this by all means enlighten me.