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Re: Old plasma screen Y_SUS anomalies

After replacing the 74AC540s on the YSUS board, a 2nd buffer board replacement didn't pop it's top 47R resistor - although I'm only running the device long enough to scope a few waveforms and take a few screen shots - so I don't know for sure whether the resisisor or a similar part will fail again, given the opportunity.

The buffer output voltage still does not follow the YSUS output below about -50V.

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I now get a lit panel with greenish horizontal streaks and a red-yellowish vertical section that hops back and forth across the display. This was what I was looking at for very short time periods, previously, before the buffer board resistor failure blanked out the bottom sections.

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Do I need a white screen (or any) input signal to go further? Most TV's have a built-in "no signal source detected' display pattern . . .

RL

Reply to
legg
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The TV will produce an "input" legend at the the top of the screen when it's turned on, and a "no signal" message will appear after about 10 seconds of no signal. The TV's control board most likely has a built in pattern generator that will help isolate a no image complaint to either the main or control board assuming the rest of the boards are working. It's been a long time since I repaired those tanks so my memory isn't great on them - but if the control board has a separate harness that plugs into the power supply, the procedure was to remove the connector from the control to the main and jump two pins on the control board. That would put it in a pattern mode. I'm pretty sure I tossed all the training manuals for those but I'll check next week when I get back to the shop.

Reply to
ohg...

On Fri, 12 Nov 2021 13:34:55 -0800 (PST), " snipped-for-privacy@gmail.com" snipped-for-privacy@gmail.com wrote: <snip>

I don't see many screen pattern disgnostic images that resemble what I'm looking at. Most shots that show full-screen random or shifting patterns refer to connector errors or to (agh!) scrambled control boards.

The 74AC541 parts on the control connector input end of YSUS weren't replaced - only because they were hidden when the parts order went in - and they have a different body size than the rare 74AC540S part at the other end of the board. Talk about board revisions between models, this one is obviously a mid-revision of itself . . . . .

RL

Reply to
legg
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The small control board actually sending drive signals to YSUS (flat ribbon), ZSUS (10pin bundle) and the bottom Xrow boards (flat ribbon x2) has no direct connection to the power board.I believe it gets some power from the YSUS board. YSUS also seems to supply power to XrowR through an 8pin bundle.

The main control board with connex to all the I/O has three harnesses going directly to the power board. It connects to the smaller display control board using a high density shielded cable.

I've checked connectors and their insertion/cleanliness. The high density shielded parts are obviously not meant to be fooled with, much. The adhesive on shielding tape holding plugs in place won't last forever.

Flat cables from the screen to the 2nd replacement buffer board didn't like the fit. The newer rev socket seemed to stress them - could not avoid some distortion around the alignment shoulders, with less play in their strain loop area. Don't think these cables are up to many more removal or insertion cycles.

RL

Reply to
legg

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