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Dead DOS computer

Posted: Tue Jan 19, 2010 1:57 pm
by jwax
We have an old piece of equipment that has an embedded 486 processor, and runs (used to) on DOS.
The old RGA monitor died, and instead of fixing it again, I opted for a cute little converter that allows the RGA output to convert to VGA, so I can use a standard VGA monitor. It lights up during boot attempts, but then goes dark.
Problem is, after sitting for a year, the AA battery CMOS backup cells corroded. I replaced those, but the old PC fails to boot. I have 3 1/2" floppy boot disks, but the "A" drive never even lights up to try and boot from the floppy. Can't be sure, but I don't think the hard drive is even spinning up, although power is on it. F8, F11 F-anything does nothing.
Hint: The keyboard used to light the three lights above the numeric keyboard, but now only the middle one flashes during startup attempts.
Any other ideas on getting this thing to boot up?

Re: Dead DOS computer

Posted: Tue Jan 19, 2010 2:07 pm
by CeaSaR
Have you verified all sections of the power supply? You should be able to get at least something showing
a memtest etc. Possibly you might need to reseat chips and other connectors to make sure everything
else is making contact. Any number of unconnected/oxidized connections can cause non-boot. What else
have you found?


Re: Dead DOS computer

Posted: Tue Jan 19, 2010 2:46 pm
by MrAl
Hi John,

Well if all else fails you can pull the hard drive and install it into another computer.
At least that will get you going.

Re: Dead DOS computer

Posted: Tue Jan 19, 2010 5:04 pm
by haklesup
On the chance that the adapter is mucking it up, try booting without any monitor. The drives should spin up and the keyboard reset but you may also get some beeps because the monitor is not detected.

RGA, Is that like EGA or CGA? or is it a typo for RGB?

since he said it was embedded, I doubt tossing the HDD in a new PC would work. Besides he probaly needs a particular interface like ISA which you won't find on new hardware.

Re: Dead DOS computer

Posted: Tue Jan 19, 2010 6:37 pm
by kheston
A client had a custom program running in DOS for years until the motherboard quit. I was asked to write a Windows version of the program, but I needed to see how the old DOS version worked. Instead of trying to make DOS work with modern hardware, I used the free version of VMware. It worked perfectly, still does. If the DOS machine in question doesn't have any weird peripherals you need to keep using, perhaps you can do something similar.

Whatever you do, might I suggest placing the hard disk into a working machine and imaging it? Not sure if there's stuff there you're worried about losing, but if the motherboard quit, perhaps the drive is next.

Re: Dead DOS computer

Posted: Wed Jan 20, 2010 7:10 am
by dyarker
If the CMOS memory RAM battery went dead then the CMOS memory has "forgotten" EVERYTHING. Which drive to boot from, hard disk sectors per track, tracks per platter, number of platters, etc. I seem to recall that getting to BIOS setup took more than one key to get to, and was different for different motherboards/SBCs/CPU boards. The key combo is programmed into the PROM/EPROM.

Step 1 - Clean/replace battery holder, install new battery. The boot start code in PROM/EPROM will quit early if it can't find CMOS memory (empty or not). Now power up and see if you can get into BIOS mode.

(On older harddrives sector/cylinder/track/preemphasis info was on a label on the drive.)

That ought to get you started.


Re: Dead DOS computer

Posted: Wed Jan 20, 2010 9:45 am
by KevinL
in most of the computers during the 486 time frame used the 'del' to entry bois setup..

the first thing I still do to service old Dos computer is to first verify the power, min to see is +12 & + 5... -12 is mainly for serial ports...

you can start with minimum machine by disconnecting the power to hard & floppy drives, remove all cards but video..

then boot, machine should do a power on reset at keyboard with light flash and beep on the speaker..
if no beep then remove video card and power up again.. should hear 7 short beeps followed by a longer beep which means video card troubles... I don't remember the beeps for memory errors but there's beeps for that also but machine should boot to video if the first 64K to maybe 256K is good durng boot up...

if video card works correctly you should see enough info on the screen to help in troubleshooting from there..
you should memory check by the memory size counting up and will be a bios error, if it does not match what's in the bios....
most troubles shoud be on screen like:
no hard controller if bois has info about hard drive...
no floppy drive, if a floppy is set in the bios...

once you can get the bios to set the time & date and stay set after a medimum power off, then the battery and battery circuit checks out..

from here you set the bios for the floppy drive, hard drive and maybe even the parallel and serial ports on some boards..

good luck...

Re: Dead DOS computer

Posted: Wed Jan 20, 2010 1:37 pm
by Janitor Tzap
Oh Boy,

Well, lets first do this logically.

Step One: Disconnect Monitor, Mouse, Printer, External Modem.
Leave the Keyboard connected.

Step Two: Try powering it up.
You should start hearing beeps, and the drives should start up.
{If you get nothing, move on to Step Three.}
If it beeps.
Shut down, and connect one at a time, the other External Devices.
Trying each till you find the one that stops the computer from beeping at all.
That is the problem component, that is causing it not to boot.

Step Three: Open up the case and strip out all boards, including memory sticks.
And disconnect all drives.
Power up the board.
It should start beeping right away.
{If you still get nothing, move on to Step Four.}
Now replace Memory Sticks first, and do as before.
Checking each component until the computer stops beeping.

Step Four: Check for the CMOs/BIOs Reset Jumper.
If the jumper is set to the reset, the computer won't boot.
Or you said that the batteries had leaked.
Normally this jumper is near by the battery connector.
So check if this has caused a short, or any where else on the mother board.
{If you still get nothing, move on to Step Five.}

Step Five: Check voltages from the power supply.
If voltages are missing, then you'll need to repair, or replace the supply.
Power Supply checks out fine.
You are in a world of hurt then aren't you. :(
Because that means the CPU, or the Mother Board has died.
If this is the case....
You may get lucky, and it is just failed electrolytic capacitors on the old Mother Board.
Other then that....
You may be able to find another old computer that you can jury-rig, to get it too work.

Signed: Janitor Tzap

Re: Dead DOS computer

Posted: Mon Feb 01, 2010 12:23 pm
by jwax
Power Supply voltages are normal.
A minute after powering up, I get a short "raspberry", then two short beeps.
Next I'll start pulling off cables, disconnecting things one by one.
Thanks for the help guys!

Re: Dead DOS computer

Posted: Mon Feb 01, 2010 3:00 pm
by Janitor Tzap
That beep code sounds like its the CGA Video Card, that its complaining about.

Here's a site that has Bios Beep Codes.

Signed: Janitor Tzap

Re: Dead DOS computer

Posted: Tue Feb 02, 2010 6:30 am
by KevinL
it's been a little time since I troubleshot one in the field, but you might try pulling the memory to see if the beeps change, even before pulling power cables to hard & floppy drives, no need to pull ribbon cables. I'm trying to remember if the video will display even if no memory is in the motherboard, just dont remember, but it will not hurt the computer to boot it with no memory to see if the beeps change.

if memory, some motherboards had to have a pair of memory sticks and some required 4 identical memory sticks to boot correctly.

to help with memory troubles, will need the part number of the memory chips on the memory sticks. like 4464, 4164, the memory sticks are also pickie about matching the number chips located on the stick and whether their single or double side with chips.