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I'm poking at this again.
I need to make room and it's last call on this panel before it's off to E-waste.
Let's summarize:
-Display "ran when parked", meaning the last time I saw it working it was flawless and I was the person who turned it off without issue
-Display was left plugged in and on standby for a period of months
-When turned on you get a green LED + a relay click, the high voltage comes up, then after about two seconds the high-voltage drops, a relay releases somewhere and the green LED briefly goes out, then comes back on.
-The Pioneer manufactured PSU starts cycling a 1-long, 1-short blink error which means it has shutdown part of the PSU for some reason.
-If the panel has a valid video input and audio, even with the above the display is still responsive and has a green light on the bezel, but it's operating completely blind.
-The display never detects the PSU failure and as such the entire display never shuts down because it never detects the fault stored in the PSU.
-NEC's service manual does not list this as a potential fault scenario. It's "impossible"
-NEC's service manual does not cover the plasma display portion (sustain boards, drivers and buffers) with any technical detail, instead referring to another service manual I do not have and cannot locate.
-For a period of time I had access to a large quantity of heavily worn or defective plasma displays of the same make and model
-I salvaged two power supplies and the contents of at least two panels
-I did NOT save the correct boards that fit my revision of the display......
-Internally, the PX-42VM5A has two major board revisions. The plasma display portion is NOT interchangeable between revisions due to different connections/mounting hole placement, so I do not have any buffer, driver or sustain boards I can substitute.
-I can swap in a known good power supply and the high voltage shuts down, so the fault remains in the plasma display section and not the power supply.
-Isolating the high-voltage output of the power supply causes the PSU to not go into a partial shutdown, however the display then detects a power failure and shuts down. This is exactly how it should according to the service manual.
-The DC outputs of the power supply are all within spec. The high voltage however shuts down too quickly for me to measure the loading of the voltage rail
End of summary.
Since high voltage comes up consistently and remains stable until the partial shutdown I can only guess that nothing between the PSU and the panel itself is dead-shorted, such as the monolithic IGBT, the drivers or the buffers, unless power is totally blocked from reaching things further downstream of the PSU until commanded. The only thing I can guess is when the panel tries to "strike" (the panel brings up the cells to their illuminated idle state) is the point where the PSU detects something abnormal. I'm not sure how the initial striking process works on a plasma panel but I am assuming this requires either a boost circuit or inrush protection provided by one of the many high voltage capacitors. In comparison to newer plasma panels there are considerably more of them in this TV.
Why am I dragging my butt rather than recapping? Price.
There's over $40 in capacitors to replace, plus an afternoon of work at the bench. If I'm wrong I'm about to make a very costly mistake. I'm hoping to narrow this down as much as I can before pulling the trigger because if it's anything else in the circuit there is no solution because no replacement parts are available. :/
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