Bookkeeping or stored settings in the Z5 RAM go bad now and then on a game with a reset board (A24).
Intermittent bookkeeping RAM (Z5) errors: reset cable MA-796
Cause: The CPU read/write line (U1 pin 34) is too weak to drive the Z5 RAM reliably, and the control board and reset board reset outputs are tied together.
Checks
- Look at the cable from the reset board to the control board at plug A24P2.
- See whether a 3 k resistor sits across pins 7 and 11 and a diode sits between pins 17 and 24 of that plug.
Fix
- Fit the MA-796 cable, or add the parts to the existing one: a 3 k 1/4 W resistor (XO-23) from pin 7 to pin 11 of A24P2, and a 1N270 diode (XO-265) from pin 17 to pin 24.
- Move the wire that was on pin 17 over to pin 24.
Systems
Related tips
- Control board MA-774 is a drop-in for MA-647
- How System 80A differs from System 80
- Control board MA-291: main chips and battery
Source: Premier Technology Parts Catalog (System 80, 80A and 80B), Gottlieb / Premier