After repairing battery-leak damage on the CPU board, the game boots with sound, display and most lamps working, but the I/O board's blanking LED keeps flashing and lamp rows 1 and 3 do nothing in the lamp row test.
Whitestar: I/O board blanking LED flashes, lamp rows 1 and 3 dead: data bus short
Cause: A solder short on the CPU board between data bus lines D0 and D2 just after the 74HC245 bus buffer. The two lines are not next to each other, so checking only neighbouring pins missed it. D0 also drives the I/O board's watchdog, which is why blanking never released.
Checks
- Compare the D0 signal with a working data line (such as D1) on a scope or logic probe at the buffer and at the I/O board.
- With the power off, check every data line against every other one for a short, not just adjacent pins, especially around reworked chips and traces.
- Check the ribbon cable and its header pins for corrosion damage too.
Fix
- Find and remove the solder bridge (or damaged trace) joining the two data lines.
Systems
Related tips
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- One flipper flips but has a weak hold and drops when hit: bad transistor at Q16
- F7 blows at power-up: flasher socket tabs touching, which also shorted Q27
- Resets when the flippers are used: arcing flipper coil, then bridge rectifier BR21
Source: Pinball Repair help group!! (Facebook group)