Electronic Technical Enterprises








The early Bally electronic pinballs have a green LED that flashes 7 times on a normal startup. If it does not flash all seven times, then the following are indicated as potential problems. A picture is shown at the bottom of this page.

CAUTION! If you attempt repair on your MPU board and it is unsuccessful, then you will only drive up the ultimate cost of repair. Be sure you have adequate soldering and board repair skills before you begin work. We recommend you cut the pins loose from the chip in question from the top, then pull the pins out from the top while heating the pad to minimize damage. Battery corrosion damage must be repaired, then the area cleaned with dilute vinegar, then clean water to stop further corrosion.

The following is a list of potential causes for failing to complete the 7 flash sequence. The list shows the step that was completed and what are indicated as possible repair items. The first item indicated is far and away the mostly likely, and the following items less likely. If the following designations or explantions are not sufficient, then you lack the knowledge to repair the board yourself and should have it repaired by someone with the required knowledge and experience.

  • Always off: 12 volt missing, 5 volt missing, LED circuit bad *
  • Always on: C14, C15 shorted, U16 bad, U15 bad, U9 bad, Reset line bad, valid power circuit bad, U19 bad
  • Erratic flashing: Bus bad
  • Flicker/flash: U1-U8, U10, U11, U9
  • 1 flash: U7, U9, U10, U11
  • 2 flash: U8, U9, U10, U11
  • 3 flash: U10, U9
  • 4 flash: U11, U9
  • 5 flash: Interrupt circuit fault, U11, U12, C16, C17
  • 6 flash: Interrupt circuit fault, U10, Fault in zero crossing circuit, U14, U18, U19
  • 7 flash but game operation improper: U11, U10, U20, U14, U19. Note: Good PIAs of certain brands may not function correctly in some of these machines. If a switch matrix or solenoid problem is a headscratcher, try swapping with a PIA of a different brand.


* - Test Points for voltages on the Bally MPU are: TP1: 4.75-5.25 volts (5 volts nominal), TP2: 10.5-13.3 volts (11.9 nominal), TP3: 21.5 volts, TP4: ground, TP5: 5 volts nominal.



 




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