Re: [Fwd: Diagnostic cartridges]

From: Nicolas Welte (
Date: 2002-02-05 13:47:40

Hi Nick, wrote:
> 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?

If you don't latch the ROML signal, you will only be able to see it if it
gets accessed continuously. So if the test program crashs for some reason
during the first few commands, you'll never notice this. 

A PLA failure often results in the PLA running extremely hot, so you can use
this as an additional diagnostic test :-) The last dead PLA I had was working
almost correctly except for some color RAM stuff, but still it was running
extremely hot.

> 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

I don't think so, but hot plugging cables can cause all damages you can
imagine. Also, it isn't very nice to use a reset switch that is directly
connected to the reset line. A monoflop circuit as used in the 64/128 reset
circuit is much nicer, the ripple/noise as created by a simple switch can
send the CPU into a lot of undefined stated before it starts to run.


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