[Coco] MPROM woes

[Roger Taylor]

I can't for the life of me figure out why my MPROM board will do 
everything it's supposed to do except WRITE the EPROMs.

The voltage regulator is showing Ground, 12.5v, 21v, and the source 
voltage.  I haven't checked the EPROM socket VCC pin yet.  I guess I 
need to reheat the solder joints.

The EPROMs are reporting blank and I've tried 27128, 27256, and some 
2764 clones, using the 12.5v jumper setting then the 21v, but I have 
60+ EPROMs and I doubt all of them are bad.  Most are new, so 
obviously something is going wrong on the board.

The software gets to the first write of address $0000 and reports 
"Not programmed properly" and quits.  In other words, the write 
didn't take.  Checking the EPROM again reports it to still be 
completely blank with $FF's.

-- 
Roger Taylor

http://www.wordofthedayonline.com