Re: Apple IIc going crazy, bad ROMs ?

["David Wilson" <mcs6502@gmail.com>]

Gabriele72 wrote:
> The machine powers up with the usual Apple //c [...] Check Disk Drive
> writings but also some "@" appear on the screen here and there. Despite
> what I throw in the disk drive, the machine always ends up in system
> monitor.
>
> Breaking into basic prompt is possible but basic commands return weird
> effects (the commands give the expected result followed by load of
> garbage characters). I suspect one or more bad ROMs but I can't verify.
>
> I noticed 3 socketed ROMs, 342-0133 CHARGEN (I think it's fine),
> 342-0284A MAP, and 342-0272 MON. I can burn 2716 EPROMs and up if
> needed. Any suggestion is greatly appreciated.

342-0272 is the original (ROM FF) firmware and does not have a very
good self test. If you can burn a 27256 with the ROM 00 (342-0033)
firmware and cut and solder the two jumpers on the motherboard (drop of
solder to join -(||)- and a sharp knife to cut -|><|- making it open
circuit) you will have a better self test that _may_ be able to
identify which RAM chip you need to cut out and replace (or if it is a
faulty ROM then the problem will be resolved).