I have an IBM-compatible Columbia Data Products VP Portable. I want to put my thoughts here on my troubleshooting efforts and see if anyone agrees (or not with my thought process). I bought this a few years ago (in the box!) from the original owner who said he remembered an issue with it in 1991 and he couldn't fix.
It POSTs and the keyboard has power, but it won't input.
Assuming it has the same beep codes as an IBM this would make me think system board or RAM.
When I started digging around I found that 8253 was installed backwards, Ok weird...I swapped it the right way (per the board and socket) and now it powers on, POSTs...BUT has a continuous beep (beeps FOREVER). The keyboard still gets power, but won't input.
Ok maybe that 8253 is dead (yes confirmed it's dead on another machine), put in a known good 8253 still long continuous beep.
I am thinking this isn't a RAM issue and something in the keyboard input logic. I found this thread ( https://forum.vcfed.org/index.php?threads/ibm-5150-continuous-beep-on-powerup.71222/ ) of a similar issue on an IBM that was resolved by replacing the 74LS245 Octal Bus Transceiver on U13.
Obviously, U13 isn't the same on this board, but there was masking tape on the VP's U13 which is a 74LS125....OK...i could get behind this...maybe that failed and is making the board see multiple key presses.....
Before I throw more parts at this (since I do not have a 74LS125 or 74LS245handy) what do you al think?
It POSTs and the keyboard has power, but it won't input.
Assuming it has the same beep codes as an IBM this would make me think system board or RAM.
When I started digging around I found that 8253 was installed backwards, Ok weird...I swapped it the right way (per the board and socket) and now it powers on, POSTs...BUT has a continuous beep (beeps FOREVER). The keyboard still gets power, but won't input.
Ok maybe that 8253 is dead (yes confirmed it's dead on another machine), put in a known good 8253 still long continuous beep.
I am thinking this isn't a RAM issue and something in the keyboard input logic. I found this thread ( https://forum.vcfed.org/index.php?threads/ibm-5150-continuous-beep-on-powerup.71222/ ) of a similar issue on an IBM that was resolved by replacing the 74LS245 Octal Bus Transceiver on U13.
Obviously, U13 isn't the same on this board, but there was masking tape on the VP's U13 which is a 74LS125....OK...i could get behind this...maybe that failed and is making the board see multiple key presses.....
Before I throw more parts at this (since I do not have a 74LS125 or 74LS245handy) what do you al think?