IBM Model 5160: Quick Update (27-Aug-2023)
21A quick update on my plans for my IBM PC/XT aka Model 5160.
First is converting the motherboard from a 256KB to a 640KB board. This involves replacing the 64KB (nine 4164s) in BANK 0 and BANK 1 with 256KB (nine 41256s). I'll then be able to recover a lot of nice 4164 chips from the two expansion boards I have (one for the Portable PC Model 5155 and one for the XT Model 5160).
Refer Note 1 here:
https://www.minuszerodegrees.net/5160/motherboard/5160_motherboard_revisions.htm
Second will be looking at a keyboard issue I have. The keyboard will work fine for a minute or two after booting from cold, but then will cease to work. Rebooting doesn't help ... so it's like some component is "warming up".
I did think maybe a tantalum on the motherboard had blown but they all "look" okay. So I'll pull the keyboard apart again and check there too.
But looking at the capacitors, there's several different types installed ... it looks like maybe blown tantalums have been earlier replaced? Maybe it would be good to replace all of them so they are uniform ... ?
https://www.minuszerodegrees.net/failure/failure.htm
Third, I saw a new video from @Epictronics1 where he increased his Model 5160's clock speed using a PC-SPRINT board.
https://youtu.be/DYtjLshgscY?si=-rJe8w3FU7xSOufK
However he had issues installing it due to the additional slot 8 interface in the PC/XT. So I had a fruitful discussion with @VintageSupportServices on my Discord today and we have two solutions.
My attempt is here:
https://github.com/0ddjob/pc-sprint/tree/master
Ideally you should replace the original 8088 with an NEC V20 but I don't have one handy ... but, I do have an Intel 8088-2 which is supposedly good up to 8MHz, better than the original 8088's 5MHz.
Finally, I'm going to try a genuine 720KB 3½" drive (from an Amstrad PPC640) ... a Matsushita JU-253. This has a dark grey colour and so matches the black of the PC a bit better.