RE: [Fwd: Diagnostic cartridges]
Date: 2002-02-01 05:39:54

Hi Nicolas,

>I built a hardware on my own now, which uses the concept I described in my
>previous message. I based this on a dual 8k EXROM/ROML board for a 27128
>EPROM, with a latch made from a 74LS00 to switch off the EPROM by a write
>I/O2. I rewired the LS00 to do what I needed: two NAND gates form the
RS-flipflop (/RES asserts /GAME, any access to I/O2 asserts /EXROM), 
>the other
>two gates are used to form a combined chip select from /ROMH and /ROML.
>way I could put all your code into a single 8k bank and therefore install
>different diagnostic carts in one EPROM. I'll expand this to the third

This is of course the most optimal way to do it!

I still have many dead C64's though that fail to be diagnosed by the
indicators. POWER is Ok, RESET is Ok, Clock OK, but ROML access is not (that
is the cart never starts). I assume these to be a failed 6510 or PLA. Would
that be correct?

I also blew-up my first C64 for a long time about a month ago. The only
thing I could put it down to was that I held the RESET line low (via the IEC
port) for about 1.5-2mins (was swapping a bunch of cables with the C64 "on".
The screen eventially garbled. Fortunately, it proved to be only the 6510
which was very very HOT. Is it common to kill the CPU with an extended

- Nick


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