Been slowly working on this System 11b game awhile now. Originally purchased with known issues.
http://aussiepinball.com/index.php?topic=5119.0I was looking for a bit of a challenge and to learn more about pinball repair and this machine was just what I was after.
Just want to say that I was made fully aware of all the issues by the seller and had no nasty surprises when this machine arrived.
Anyway, a breif summary of the major problem.
At powerup Cpu would boot and machine would go into attract mode but the score displays would usually show only some of the digits.
Also Cpu controlled lamps were very dim and most not working at all. When I started a game, the A/C relay in the backbox would buzz continuously as it tried to switch, and any coils that did work were very underpowered. No flippers/Pops at all. If I left the power on for awhile, it would usually warm up and the displays would gradually get more digits showing and the lights got a bit brighter. By waiting until all the displays were working you could start and play a game.
I guess my biggest problem was to identify where the problem actually was. You've got the Cpu board, power supply board and the auxillary power board, Hmm
I initially attacked the Power supply board as I figured good input voltage is a good place to start - rebuilt the high voltage section and installed new header pins and connectors which didn't really make any difference. Also found and replaced a bad diode on the Aux Power board as well as replacing the A/C relay. Still no luck.
What I really needed was another system 11 game to swap the boards. This is where the CPU tester was a great help as I could narrow the problem down to the Cpu board.
On the Cpu board, I noticed the blanking LED was also very dim. Used Leon's test rom to test all PIAs which all tested good. Also noticed by shorting pins 5 and 6 on the 555 timer chip, the blanking led became bright as well as several more CPU controlled lights were activated. Started to suspect the blanking circuit. Replaced U43 (555 timer) and Q50 (2N4403 transistor). No difference.
Several hours research later I also replaced C58 (1uf tantalum in the blanking circuit) and the system came to life. Wow!
I have used a standard electro cap that I already had here, but have ordered the correct part from GPE and will replace this when it arrives.
I had to put the board back into the game just to try it out. Displays now bright and clear except for player one which is slightly dim.
Game now starts and plays well and I have to say that I am very pleased with myself.
Still have a few problems to sort - Only 3 out of 8 lamp columns are working and some switch problems as well but now that the board boots properly, I should be able to use the Cpu tester to find/fix these, hopefully without too many problems.
Hard to believe that less than a dollars worth of parts, and particularly that little capacitor, could cause so much chaos.
