I just picked up a IIc. ROM 255. When you power it on, you get a changing pattern:
If I hit ctrl-reset, it will give me a normal boot screen, and then display the "check disk drive" message. If I hit ctrl-reset again, it will reboot to the garbled screen. When it does try to boot from the drive, I get the "check disk" message, regardless of whether I've got a disk inserted.
Occasionally, if I hit ctrl-reset rapidly, I'll get an Applesoft prompt. But even at that point, if I hit ctrl-reset (no apples held), it will reboot to the garbled screen. When I manage to get an Applesoft prompt, the keyboard is fully working.
Any suggestions on where to start?
-Jim
Oh, I've reseated the socketed chips, and I've checked the voltage rails.
You may have more than one problem.
The video garbage and cold booting issues could be indications of bad RAM. The disk message is probably due to a dirty head. One suggestion would be to upgrade the ROM so that you could invoke the built-in diagnostics. This does require some minor motherboard changes however.
I was leaning towards the ROM upgrade. That makes up my mind.
ROM upgrade went fine. MRD0 is flagged. Wonder how many others are shot.
On the bright side, I put the keyboard and drive in a "parts" IIc, and verified that the drive works fine. And the "parts" computer, as well, which is a bit ironic.
BTW, W27E257 EEPROMs are a convenient replacement for 27c256 EPROMs. Drop-in pin compatible.
-Jim