A lamp, relay or coil output on the driver board is on all the time or never comes on.
A driver board output is stuck on or dead
Cause: Most often a failed output transistor (shorted gives a constant output, open gives none); less often a 74175 latch.
Checks
- Test each output on a test fixture or in a known good game.
- For a lamp output, confirm that a high on the matching 74175 latch output turns on its lamp transistor; if the latch output never goes high, the latch is suspect.
- Check that the 7404 sound buffer inputs sit low and pulse high when sounds play.
Fix
- Replace the failed transistor (or the latch if its output is wrong).
Systems
Related tips
- How driver board coil transistors are switched
- How the System 80 driver board is laid out
- Which transistor types sit where on the driver board
- Driver board A3-J4 coil outputs
- Driver board A3-J3 lamp groups and relays
- One or more controlled lamps never light or stay on
- How driver board lamp latches work
- Driver board A3-J2 backbox lamps
Source: System 80 Service Manual, Gottlieb