After some weeks, another (rather disappointing) update:
- Finally got my hands on a spare DAC and socketed/replaced the one for Y-Out: no changes.
- Also replaced the LS164 for Z-Out, also without success. Still dead.
So, I now do have:
- Proper voltages everywhere on the board (checked and re-checked)
- X-Out: working as expected.
- Y-Out: known good TL081, TL082, DAC - seems to be somewhat active, but far too weak (already coming from the DAC, pre-amplified)
- Z-Out: known good transistors (all three of them), LS04, LS164 - dead Z-Out (I do see activity at the base of Q7, but beyond that point, the signal seems to get lost).
- Game still does play blind.
Learnings so far:
- I need to get a proper scope. The old Velleman portable is suffering from software issues and frequently locks up during normal operation.
- My lack of knowledge hits me hard here, so I'd appreciate any further hints.
Cheers,
Martin
