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Sharp Aquos LC-26P70E

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OldLes:
We found time this afternoon to knock up a 3.3v supply off the +24v on the inverter panel (with supply from bench PSU) using a couple of resistors and a 3v3 zener. Powered up, all CCFLs lit up for the normal (?) short test period, then off. Re-connected everything, but of course still nothing. The green LED on for same period as before, but nothing else. Quick check and no 3.3v present at pin 12 of CN7501 of inverter panel.
I have just spent 30 mins trying to trace it back to source, but no luck. Either its designation changes as it goes from panel to panel, or I am not looking in the right place.
May search again later, or tomorrow.
Les.

In_Focus:
OK so you're definitely dealing with an inverter issue, with your external supplies the lamps should stay lit and the fact that the set won't start is because the lamp error count has reached 5.

My next step would be to strip the screen so you can see the naked CCFLs, power on using your test supplies and I'm certain you will see one or more startup pink. These will need replacing, once you get the inverter to stay on permanently you can then try running with the sets electronics and try and get it into K mode.

Keep up the good work.

OldLes:
Right, I begin to see what you mean. Because of faulty CCFLs, the counter has decided to inhibit the 3.3v start up voltage to the inverter. But since there is NO ATTEMPT to start the inverter (other than with my independent +24v and derived +3.3v supplies), how can it ever be persuaded to display the "K"? If all the tubes were renewed now, it would not try to start up, so the "K" could never be seen.
Logical? Or have I got it wrong?
During my tests yesterday, I looked carefully at the screen, and there were definitely no missing lamps. When I checked them with my tester, there was no suggestion of pink ends, but obviously I could not see them properly.
Les.

downunder:
Hard to pick a pinkish lamp without exposing the lamp cavity....least I've never had any luck. Oldles, I tried to follow the BL-ON signal back to the main board on a schematic but it did my head in.....I failed.
Re the service mode (K mode), it has the ability to over-ride the signal and display a screen even with a faulty CCFL. If K mode cannot be accessed, I'd be inclined to blame the Main board, the same board that generates the BL-ON signal. Admire your dedication!

OldLes:
Downunder, I don't get much time to play with TVs, with major motorbike overhaul underway, plus all the MANY jobs SWMBO keeps pushing my way. (Build greenhouse, lay concrete, etc. etc.).
But, the Sharp. Pin 12 of CN7501 actually links directly to Pin 2 of CN7502, where it is labelled STB. This can be traced to mainboard 6/6 as Pin 2 of P1702. Through R1717, and then on to Pin 18 of IC1710 where it is labelled BL_ON, and shows a level of 3V3. I assume this is the source of inverter control voltage, but currently inhibited because of the lamp count. I probably won't get to look at the set until Monday, but I will see if I can do something here.
OldLes

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