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Author Topic: Tron  (Read 2572 times)
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« on: November 20, 2005, 05:03:03 PM »

No boot. Screen full of random graphic blocks.

Put the Z80 logic analyzer on the main CPU (middle board). Halt light on, no activity.

Replaced Z80. Code now runs but...

Still no boot. Screen full of random graphic blocks with moving short diagonal lines.

Traced code through to a read of the last byte of NVRAM (C7FF). It was reading FF when it should have
read 00. A peek at the schematics showed the vbatt line pulls the address/data lines on the NVRAM high.

Connecting +5 to the vbatt line caused C7FF to be read as 00 as it should, but...

Still no boot. Screen full of random blocks resetting over and over.

Watchdog is barking. Traced code to a chunk that was in an infinite loop, so the watchdog never got reset. Compared
the code to MAME and found it didn't quite match. Values were similar, but not quite right. Something was wrong with
the code above 0x705A or so. Looked at the memory map and found that address was in EPROM "C". Pulled the EPROM,
found bent pin. Pin broke off when trying to straighten.

Burned new ROM. Game now boots.
« Last Edit: November 20, 2005, 10:38:37 PM by tim » Logged
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