Well the Dragon is really messing with my mind this evening.
Powered up on DBT w 120w bulb, supplies all look good! Power off, switched to full line voltage power, supplies all look good! Back to 120w DBT, set left bias to 34 mv, no problem, power down move dragon claws to right bias test points, power up, still on 120w dbt, set right bias to 34 mv, decided to let it soak a while. A few minutes pass, something starts to smell hot
, then
FLASH an 8 inch spark blasts off from the R module
. Shut down, tested all the silicon on the module, perfect condition
. Close examination with magnifier finds a small solder blob on the top of the pcb, but not touching any components or traces.
Cleared blob, powered up on 60w dbt, no problem, powered up again on 120w dbt, no problem, DC offset good. Powered up again on full line voltage, NO problem, offset still good, all power supplies good, relay pulls in normally. Back to 120w dbt, set biases again, NO problem. Power down again, mminimize bias pots, put 5a circuit breaker in place of bulb, powered up again on full line voltage. Tickled the the dragon on left side, stable and normal at 30mv, rose a couple mv over ten minutes. Power down, move dragon claws to R side tps, power up on full line voltage. Set R bias on R side to 31mv. Sitting on full power for 50 minutes now, R bias stable at 32.5 mv.
. Power supplies mirrored and stable at +/- 40.0 vdc. Q5 mounting screw head temp stable at 37 deg C on both modules. Guess the SX-780 made its saving throw, 20/d20. (Any old DnD players?) Had enough for tonight, back at it tomorrow.