Zaccaria/Associated Leisure Mr. Do! Maintenance 2019

19/04/2020 - Game PCB #C50327 repair

Mr. Do! no boot Mr. Do! PCB on the bench Mr. Do! graphics issues

Pre-show testing encountered the game PCB not booting. The +5V in the cabinet measured OK and so the game PCB was removed for bench test.

On the bench the game PCB wasn't booting and a pass through pressing on the socketed IC's found that IC A4, EPROM D1, caused a change in video. Cleaning up the IC pins on all the socketed IC's brought the game to life but with graphics issues that did not appear to be socket related.

The background characters appeared to be split-doubled. Starting with IC W8 (2128) both address and data busses looked OK on the scope. Moving on to IC's U8 & S8 (2732) found pin 6 low, pin 7 pulsing and pin 8 pulsing. These three bits were the address bits for each column within the character with the remaining address bits selecting the character itself, so a stuck bit in column address would cause this display artifact. Moving upstream to IC T5 (LS86) pin 11 "2VC" output and pin 13 input found the input pulsing OK so I suspected IC T5 (LS86) was bad. A quick piggy-back check with a replacement IC fixed the character doubling and replacing IC T5 fixed the game.