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PS/1 2123 - Errors and dead video

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
Hi all,

Hoping that someone here can point em in the right direction of getting a recently purchased IBM 2123 up-and-running. I'm not sure if I've casued more damage but what started at two error codes (161 and 163), quickly became three (error 303) then today four (error 404)! Also, the on-board video was working fine and has now stopped. Plugging in a 16-bit ISA VGA card does give me a display so at least I can see something!

Ignoring the failure on on-board video, powering the PS/1 on gives the 2048K memory check, and the in order 304, 303, 161 and then a pause and disk access before 163. I then get two short beeps and then the graphic showing "consult the manual".

I know that the 161 and 163 are common and the CMOS battery is dead. I've replaced the CR2032 but still see the 161 and 163. Am I right in thinking that both of these will remain until I get in to the disk-based config program? Or should the 161 error have now disappeared after replacing a battery? I do have the disk and it loads to the blue IBM screen, but as the keyboard does not work I can go no further :-(

I'm more concerned about the 303/304 errors. I see that these are keyboard-related - or possibly keyboard controller related. I have tried two PS/2 type keyboards - a fairly modern HP one and an older Compaq one. Both of these keyboards now have the same symptoms. Up until today they only gave the 303, but the 304 is new and worrying. Could it simply not like either keyboard? I did have one of them working - very briefly and only once - just after I got the PS/1 but then the 303 error appeared. I have read that this may be capacitor related, but I've no idea which ones on a 2123 board.

I've checked the PSU rails and all fine.

Any help or pointers gratefully accepted! The case is in good condition and I'd like to get this up-and-running if i can.

Thanks,

Dave

PS: Hopefully this post won't appear twice. I'm sure I created it once already but apparently I've made zero posts. So apologies if there are two of the same post.
 

IBMMuseum

Veteran Member
Joined
Aug 28, 2006
Messages
1,394
The PS/1 "Pro" 2123 was going to be the PS/2 "Model 30SX" - same planar (with RAM and video connection changes) as the 25SX. You need a keyboard that is closer to the same age. I can see what might be the best way to proceed.
 

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
Thanks for the reply. I've since received a Model M keyboard and tried that, but get the same problem.

There seems to be no visible signs of damage to the system board and the keyboard socket looks to be ok (no corrosion, no cracked or dry solder joints) so wondering if this might be more a chip or component failure. Unfortunately I really have no idea where to start.
 

IBMMuseum

Veteran Member
Joined
Aug 28, 2006
Messages
1,394
Thanks for the reply. I've since received a Model M keyboard and tried that, but get the same problem.

There seems to be no visible signs of damage to the system board and the keyboard socket looks to be ok (no corrosion, no cracked or dry solder joints) so wondering if this might be more a chip or component failure. Unfortunately I really have no idea where to start.

Are you able to toggle keyboard LEDs? 'F3' is a keyboard fuse. I can't read the rating even with the hi-res images I have, but I have a 25SX that I can look at directly in a few hours.

http://ibmmuseum.com/Planars/Model 25SX/Model25SX-16-L.jpg
http://ibmmuseum.com/Planars/Model 25SX/Model25SX-20-K.jpg
http://ibmmuseum.com/Planars/Model 25SX/Model25SX-Reverse.jpg
 

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
I’m travelling for a couple of days but do remember the F3 component for a reason.

When I power up all three keyboard LEDs flash briefly so not sure what that means about the fuse, but it looks like it may be OK. Before the 304 error started, you would also see the Num Lock LED illuminate if that key pressed (if I remember correctly).

As for the fuse, I’ll have to take a proper look but it stuck in my mind as there was a thin wire across the side - it may have been connecting the two pins so I wonder if someone have jury-rigged it in the past. Not sure I can post images just yet, but if I can I will once I return.
 

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
I've just checked the F3 fuse with a continuity meter and it seems to be OK. This is no doubt helped by the fact that there is a wire link between the two ends of the fuse, so looks like someone has bypassed it.

Assuming that this bypass hasn't caused larger issues on the board, what is next in the signal path? There's very little information on the 2123 - I did see reference to it using a "8042AH Universal Peripheral Interface 8-bit Slave Microcontroller" but can;t see one of these on the planar.

Thanks,

Dave
 

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
Ah yes.

So, I'm not really sure what I can check on the PLCC, being programmable and I've no idea how the thing's inputs/output is configured, but I have verified that it is getting a 5.1V supply, so at least power is getting to it.

I've had a multimeter on the keyboard socket and it too is getting a 5.14V supply. Interestingly (or maybe not as I've no idea if what I'm doing proves anything) but the CLK line sits at 1.77V regardless of there being a keyboard plugged in or not and the DATA line:

- sits at 5.14V with no keyboard
- sits at slightly less than 5.14V with a model M and voltage drops a few millivolts when a key is pressed.
- sits at 2.6V with an old Compaq PS/2 keyboard plugged in.

I suspect that the voltage readings on the CLK and DATA lines are meaningless as I'm sure I'd need a data probe to see what's really going on. However, I'm assuming that the CLK line is driven by the 8042AH and the DATA line feeds back to the 8042AH - I just don't know where! Really struggling on this!
 

dhoggan

New Member
Joined
Jan 22, 2021
Messages
6
Hi,

Apologies at resurrecting this old thread, but I'm really keen to get the 2123 working. Can anyone suggest anything based upon the above findings?
 
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