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POST Diagnostic Cards, 8 Bit ISA, Useful?

mmruzek

mmruzek

Experienced Member
Joined
Sep 28, 2011
Messages
232
Location
Michigan, USA
I see many POST diagnostic cards for sale on EBAY that are 8 bit ISA compatible and only cost a few dollars... Do they have any value for repair/trouble shooting of older systems such as the IBM 5150 PC? Can anyone suggest a specific card that might be 'best in class'? Thank You, Michael
 
POST cards appeared around the time of the AT. The IBM AT BIOS outputs codes to port 80h, and so the vast majority of POST cards will be monitoring port 80h.
Other machines started to output on different ports. The following list is from the manual for my 'Micro 2000' POST card:

Port 80h = standard usage
Port 84h = All Compaq computers
Port 90h = PS/2 models 25 and 30
Port 300h = Award BIOS
Port 680h = Computers with Microchannel bus

Therefore some POST cards will have switches/jumpers to change which port is being monitored.

IBM XT

The IBM 5160 BIOS outputs only a few POST codes and does so to port 60h.
Someone has listed those codes at http://www.61131568.com/E_ibmxt.asp
I have yet to see a POST card that monitors that port.

As for XT clones, I would expect that some BIOS manufacturers added the code to their XT BIOS after they saw the technique introduced in the IBM 5170 (or was it that IBM copied the technique from some other manufacturer).

IBM PC

Won't work.
 
If you buy one of the cheap ones from eBay, do not believe the claim that you can insert them into an ISA slot backwards without harm!. I took out a southbridge chip on a P1 system that way.
 
I got one of those cheap ebay cards, they work ok for what they do.

Also purchased the laptop one that works on the parallel port.

I tried inserting the ISA one backwards, it makes the PS not start up (never tried plugging it in when the thing is running which is VERY bad for any card). Since the PS didnt start up I think something was shorting to ground. This was on an AT system, no idea what happens with ATX.

Be aware you need to look up the 2 digit code using the correct type of BIOS in the provided manual and then trouble shoot why the system isn't working.
 
mmruzek said:
Do they have any value for repair/trouble shooting of older systems such as the IBM 5150 PC?
Click to expand...
Already in 1987 I built my own one and still use it! At the moment I'm trying to create my own BIOS (not from scratch) and use it for debugging: just throw in a handfull of OUT commands and if an expected code doesn't appear on the screen or one appears you didn't expect, there is either an error in your code or you misunderstood things.

Groetjes, Ruud Baltissen
www.Baltissen.org
 
Doesnt work on XT to me.. Yes you can put them in the slot and the display will lit but no more then that..
 
Yes, that's been my experience as well.

I've plugged any one of the 3 I have (first one cost me about 500 bucks with a bunch of diagnostic software) in backwards a number of times and you don't get any meaningful display, but, they've never been damaged or damaged anything else.

However, a little arrow and the words "towards back" wouldn't have killed them.
 
On mine, the reverse on an old HP Vectra VL P1 system toasted the GALs and the Southbridge chip. The smell of magic smoke was definitely present.

So be careful.
 
I put it in the wrong direction for the first try.. Didnt know which side was meaned to be the back side.. But was happy nothing getting to burn inside the isa slot..

Then i thought, i have it in the wrong direction.. So i turned it 180 degrees.. But nothing special to see on the display..

The back side is the side of the slot brackets..
 
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