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IBM 5120 - Strange "ABCDEFGHJKLMN" error

Vailen

Member
Joined
May 27, 2024
Messages
38
Location
New Jersey
My IBM 5120 was working fine earlier this morning. When I turned it on a short while ago, I encountered this error:

ABCDEFGHJKLMN

Also, the "Process Check" light stays on (when it should turn off after the boot-up process is complete).

Now I am unable to complete the boot process to get to starting screen where I can enter BASIC commands and use the computer.

Does anyone know what this means?
 

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The 5100, 5110, and 5120 all print alphabet letters to the screen when they run their power-on self tests. A halt at one of the letters and a PROCESS CHECK means one of the tests has failed.

PDF page 189 of the 5120 Maintenance Information Manual says that N is a "Feature ROS check". "ROS" is IBMese for ROM, and while I'm more familiar with the 5100 than the 5110/5120, I think a feature ROS is a ROM containing things like the code for the BASIC interpreter on your machine.

Whatever it is, it's malfunctioning, Something could be wrong with its circuitry, but you could be lucky --- try re-seating the circuit boards in the card cage and cross your fingers?
 
The "Feature ROS" was just the disk sorting feature. For just tooling around in BASIC, you won't need that. It should be in Slot K and be a "half width" card. They may be somewhat snug, but a gentle pull should lift the card out (maybe slightly rock it side to side). Unless you have a working disk drive, this card won't ever be useful (my understanding is it contains a little memory buffer, and some ROS software to effectively be able to swap-files and facilitate sorting).

This Feature ROS wasn't in the 5100, but is identical between the 5110 and 5120. If you still get startup issues, try removing the RWS (RAM/memory) at the end if you have 64K (and try just 32K or swapping the ram cards) - which is essentially suggesting re-seating the cards like stepleton said.

I had one 5110 with a lazy Executive ROS, I end up having to RESET that system about 10 times before it will finally start booting. So you could try that, just let the system warm up for a few minutes, then reset a few times.
 
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