ArcadeCollecting.com
Welcome, Guest. Please login or register.
June 18, 2019, 06:17:53 PM

Login with username, password and session length
Search:     Advanced search
Yay, a message board!
319 Posts in 114 Topics by 43 Members
Latest Member: deejaymc
* Home Help Search Login Register
+  ArcadeCollecting.com
|-+  General Category
| |-+  Repair logs
| | |-+  Tron
« previous next »
Pages: [1] Print
Author Topic: Tron  (Read 2146 times)
tim
Administrator
Full Member
*****
Posts: 166


View Profile
« on: November 20, 2005, 05:03:03 PM »

Symptom
No boot. Screen full of random graphic blocks.

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

Fix
Replaced Z80. Code now runs but...

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

Tests
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.

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

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

Tests
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.

Fix
Burned new ROM. Game now boots.
« Last Edit: November 20, 2005, 10:38:37 PM by tim » Logged
Pages: [1] Print 
« previous next »
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.19 | SMF © 2013, Simple Machines Valid XHTML 1.0! Valid CSS!