My next repair project is this Sony MSX2 computer. Purchased as not working (black screen).
Unfortunately this machine has a bit more to its history than the eBay advert let on. Upon opening it I noticed that the problematic HIC1 board (The video out multiplexer that tends to suffer from corrosion on these machines) was not only missing, but pin headers had been fitted in its place.
This tells me two things. The hic board on this machine had indeed failed. But also, someone had replaced it with the modern replacement hic board but I guess it still didn’t fix the problem so they took it back out and sold the computer.
So, I need to either build or source a hic board for starters. But even then I probably still need to get the actual machine running.
I have already gone over the board with my scope to see if I can see what is going on. For starters it seems the computer tries to start for a few seconds and then comes to a stop. I can see a horizontal sync and csync but it appears the video signal is just a black screen.
I’ve also noticed that the CAS signal for the system memory is not there. Currently I’m assuming a possible memory fault so I will try swapping that out first. If it still doesn’t appear to be running then I will probably look into the ROM chip next.
All of this is under the assumption that the MSX2 should actually run fine even without the hic board present. Unfortunately I don’t have another MSX2 to test this theory.
This is going to be fun 😁
If you get a sync signal and a black screen, first thing to check/replace is the on-board RAM.
I have already ordered some replacement RAM as that is my suspicion, have also ordered a DRAM tester as I think that will be a useful tool to have sitting around 🙂
Also, this board has extra tracks on the bottom side (green ones). Those are fragile, so please check if all of them are intact.