Re: Help diagnosing a SX64..

Hi Martijn,

Unless a ROM is internally shorted, you should be able to run the machine from an Ultimax-style cartridge. They bypass all the ROMs.

It's something to try...

--
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Pete Rittwage
http://rittwage.com

C64 Preservation Project
http://c64preservation.com

Martijn van Buul wrote:
Hiya.

Right now, I'm in the US for a long overdue holliday with my girlfriend. Upon arrival, she surprised me with an SX64, which was unfortunately DOA. Supposedly, the unit got stored in working condition a few years ago,
but had died upon retrieval. I'm having a hard time troubleshooting this beast;
it's showing some mode of failure I have never encountered before. The fact
that I don't have a known-to-be-good C64 lying around which I could use to swap
components with isn't really helping. In fact, my diagnostic tools are limited
to a DVM. Maybe somebody else can help.

It's showing a strange horizontal colorbar pattern. I've taken the liberty of making a picture of it:

http://www.stack.nl/~martijnb/colorbars.jpg

The pattern is mostly stable, except for some minor jitter, but most of the
green bars are flashing. If I hit restore, it toggles between the above
pattern and a running pattern of dark grey, purple and yellow bars. Also,
the "sound effects" change slightly. No other keys produce any noticable
effect (Well, except for the shift/lock key led, but that's hardly noteworthy)

I've been doing some basic troubleshooting myself, but couldn't quite come to a
conclusion:

0) The drive seems to spin up normally.
1) None of the chips run excessively hot.
2) Removing the IO daughterboard containing both CIAs didn't make any difference, neither did removing the SID or the character ROM.
3) Removing the CPU, PLA or any of the other ROMs produces a grey screen.

I tried reseating all of the socketed chips, but to no avail. There's no
visible damage whatsoever; the machine is in a pristine condition.

Any hint would be most welcome. At this point, I'm considering a broken
ROM myself, but other opinions are most welcome.

Assuming that it *is* a bad ROM; would swapping with a regular C64 be useful?
I know that the SX had different ROMS, but it should be able to run on normal ROMs, right?




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