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I've become responsible for reviving a Tempest upright that burnt out (literally, as in a plume of smoke was rising from it) on location. After cleaning up the smoke mess and rebuilding the monitor, got the usual half-collapse on one vertical half of the screen. After completely rebuilding the monitor with an Alan-1 XY board and TUK, we fixed the half-collapse and started seeing a very weird "diagonal" collapse where both the top-left and bottom-right corners would kind of collapse towards the center in scenes with a lot of bright vectors, including the title sequence and triangular tube scene in the attract loop. I don't have video of that at the moment (working on getting it from my fellow tech) but some work that he did on the game board (again, working on details, but definitely including replacing the six X/Y pots) this was reduced to more of a "bounce" during the title sequence when the "TEMPEST" title is at its brightest.

Things that we've done so far:
  1. Totally rebuilt the monitor. HV has new flyback, new caps, new resistors (except for a couple oddball values we didn't have in stock and weren't roasted on the original) and everything else transferred to a fresh PCB from Arcade Jason. Deflection transistors and XY board totally replaced with upgrade kit from Alan-1. Confirmed correct behavior by hooking up the monitor harness to a known-good Star Wars UR. At this point I can say with confidence that whatever the issue is, it's not the monitor.
  2. Unidentified parts swaps in the analog output stage from another Tempest boardset. I didn't do this work and the other tech didn't leave a written worklog. I'm following up with him and when I have more details I'll edit this post with the scoop. EDIT: Most devices on the analog output section (with the exception of one DAC) were socketed already, and the XY op-amps were swapped (X->Y, Y->X) to no effect.
  3. What I know for a fact the other tech did: replaced all six XY vector adjustment pots on the vector board with new ones from APAR. After (2) and (3) the partial collapse stopped appearing in the gameplay parts of the attract loop and reduced in severity during the title sequence.
At this point I'm at a loss as to what the issue could be, and loath to deploy the parts shotgun for something as finicky (and expensive) as a Tempest. Any help from the vector gurus here would be greatly appreciated.
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