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x68000 Expert with strange video problem - no backgrounds in some games - FIXED!

Started by TheRealAnubis, June 18, 2019, 03:37:43 am

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TheRealAnubis

Hi everyone,

It's been a bit since I've been able to get back into my X68000 Expert and get it working again - I had a strange problem where the background (or parts of the background) of some games would be black/missing.  Many games played fine, but Mahou Daisakusen and Cliss, for two examples, had missing or partial backgrounds.

I ran the Memtest RAM checker and it reported all good..

I finally got a hold of a schematic and figured it was likely to be the RAM right off of the Cynthia chip, so I ordered replacements and started working - the problem was fixed on the 2nd IC that I socketed and replaced!  (MB81C78A-45P-SK)

Upon reassembly, the machine wouldn't boot, and there were garbled characters on the screen.  I was in the process of moving, so I had to admit defeat and pack everything up.
Three short years later, I got it back out to have another look, and the length of the RAM's IC pins were the tiniest bit longer than the originals, which was causing the machine to not boot now, and the garbled characters.  It was such a small amount that I didn't notice it, and I usually notice stuff like that..

After getting the pins out of the way by making a small bend in each pin, then getting it all back together again (and minus the metal pan just in case) it works great!  I've loaded up a bunch of games and all the graphics seem to be there.
It was a strange problem, but hopefully this info will help someone keep their X68K alive!  The repair wasn't too difficult - you just have to be extra careful with the removal of the old RAM.

Sorry for the crummy pix, but at the time, I was in a hurry and got what my sorry phone would take - you get the idea, though..

Picture 1 - Mahou Daisakusen gameplay - the area under my ship stayed blank, but the area under the 'boss' moved with him.
Picture 2 - Cliss gameplay - terrible picture, but as you can see, no background at all.
Picture 3 - The RAM checker saying all is OK - I ran this overnight with the same results.
Picture 4 - The area of the motherboard containing the RAM chips that had a problem - Cynthia chip is the large one to the left.
Picture 5 - Cliss with the background after the RAM repair.
Picture 6 - Garbled boot screen after assembly.