While still waiting for revised boards, I thought I'd give a run to my new rework setup - a Pace SX90 w/ an MBT PS (which I'm just in love with, BTW... Highly recommended).
Recapping is the obvious use for this rig, and so I started looking at the boards a little closer, and noticed that C6 on A5 (Output/HV Control) was leaked and corroded a bunch of resistors in its proximity (see pic). I haven't noticed this before - my bad. Damage was so bad, R9 essentially seem to have had one leg almost severed (not not glaringly obvious, at least until I tried to remove it, and one leg just came off). I went ahead and replaced C6, R9, R10, and - why not? - recapped the entire board. The SX90 IS that much fun.
Upon putting it back, I see the same warning lights and all, and think - darn, no progress... - but as I'm thinking this, C18 literally blew up. Brand new cap, correctly polarized, voltage rating exceeding original... What gives? I feel this may be hitting at the core of at least one issue with this unit, though what that is exactly, I am still processing.
For instance, why is C18 (and C17, for that matter) only rated for 35V? (see enclosed pic) They seem to (potentially?) be exposed to 175V... Is there a floating ground aspect here I need to factor in (reducing exactly how much those caps are "seeing?").
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I ran the unit with A5 pulled and it seems to exhibit the same behavior as before (same blinking LEDs on the controller board, no PS errors LEDs on, same "8000000" on the left screen and "squares...1/squares...0...." on the right screen). Back to the drawing board.