Commando Repair Logs
Repairer: Paul Swan
BOARD NO: 0046
(1) The background was corrupted during game play
(2) The sound volume was very low.
(1) Flexing and tapping the top board made the problem worse and intermittent. Changing the ribbon cables had no effect - the fault was definately on the top board. The nature of the corruption was that large graphic blocks contained the wrong peices of backgroung in some columns, and this was carried down the screen as the screen scrolled down. This suggested the the background RAM was either not being loaded correctly or the output of the RAM that was used as the character (ROM) address was being corrupted. Re-soledring the top left ribbon connector, the video RAM, the ROM address latches above the RAM and four or five miscellaneous TTL chips directly below the RAM fixed the game.
(2) Visual inspection and trace of the speaker pin back to the amp revealed a leaking 1000uF capacitor with a leg partially pulled out. Replacing it fixed the sound.
Forum Thread: Commando PCB Repair
Symptom: Very ‘snowy’ video
Cure: Bad output on pin 12 of the LS273 at location 4B of the smaller top board
Symptom: When powered on the copyright text appears (ie 'typed') too fast and the static attract screens are cycled through too fast, sometimes with text and or sprites missing, and sometimes with text added (see Diagnosis for more info)
Diagnosis: However, when inserting a coin the 'CREDIT 00' text either doesn't appear or doesn't count up as the board is coined up - sometimes an audible sound is played to indicate a coin up, but sometimes not. Either way, the coin ups ARE recognised (as the game WILL start).
Also, when coined up, the screen saying to press 1 or 2 player startdoes NOT appear.
On pressing the coin up button then player 1 or 2 start, the game starts and plays perfectly. No problems with sound, graphics, etc.
All EPROMs are fine.
Cure: Replaced LS74 at 6M on centre board (chip had bad outputs)
Repair Logs converted to wiki format by Brad from Aussie Arcade.