Sharp Aquos LC-26P70E

[OldLes]

Yet another Sharp has come my way, and has me scratching my head again. This initially simply went straight to a red LED. Having heard of problems with the touch panel, we looked at that first. The prog and vol controls are the normal tact switches, but the on-off switch looked odd, and it did not pop out when button released. Pulling it out, then pressing it and pulling back again brought up the sound of a relay operating, but after about 5 seconds, back to red LED with relay off.
I removed the switch, and found I could dismantle it, only to find (well, NOT find) a tiny compression switch which had gone AWOL. Somebody had been there and obviously lost it! I must have more than 1,000 springs, but no compression spring that small; by chance I found a tiny tension spring, so a bit of stretching had something to fit.
I located a copy of the service manual, and found all the supplies were present and correct for the duration of "relay ON" period. No light from the CCFLs, but checking them with my tester had them all lighting up OK.
Not surprisingly, I now suspect the inverter board, but wonder if there are any suggestions from anybody here.
Les.

[In_Focus]

Yes, the on off switch was a cheap and nasty affair on this model.

It sounds like the lamp error count has reached its limit. Try putting the set in "K" mode by applying power whilst holding down volume- and AV then pressing volume- and channel down.

Hopefully should get you some sort of display, look for the usual Sharp problem of one or more of the lamps coming on pink for the first few seconds.

[OldLes]

In Focus, we tried getting into the factory menu, but no sign of anything on screen. There is no CCFL activity at all as far as I can tell.
Les.

[In_Focus]

Were you able to get the front LED to go green? If not you could a have corrupt eeprom which may not be recoverable. If I remember the inverter is similar to the earlier P50, you could try some resistance checks on the many optos on the inverter.

Not easy to fault find these Sharps.

[OldLes]

Hi, In Focus. Let me clarify.
Plug in mains cable. Nothing. Press "ON" button, hear relay, then very brief Red LED, and then Green LED for between 4 and 5 seconds, hear relay open, and all LEDs OFF.
If "ON" is pressed again, relay, red, green (4-5 secs) and relay sequence exactly as above.

During the Green ON period, ALL power rails are present, and all decay slowly after relay opens.
The +24v is present on inverter board, but no visual response.
No optos on inverter board, but I guess you meant on the PSU board.
The inverter board is No.  RUNTKA213WJZZ (5X).
I did all the simple checks there without power. All seven transformers had identical resistances, both fuses OK, no visual problems. I think I will next see what happens if I power the inverter from my bench PSU, when I can access both side of board, and maybe hang a few spare CCFLs to see if any activity to show. There certainly is no activity from the CCFLs in the set.
Les.

[In_Focus]

Something that has just come to mind is that some models would shut down due to the inverter pcb screws being loose. Does sound like an inverter issue but the lamp error counter makes life very difficult with Sharp.

I remember now the inverter is very different to as there are 20 or more optos on the P50 series, I suspect you may need to disable the protection circuit if possible as with the D44 series to progress.

Good luck.

[OldLes]

Over the weekend, I found a few minutes to get the inverter board on the bench, with ONLY a 24v supply from the bench PSU. I am working on the assumption that it would perform OK for a few seconds. Nothing happened. Voltage at the inverter control IC (BD9883FV) pin 20, BUT no Vcc (REG) output at pin 19.
I may try putting +5v on 19 to see if anything happens, but I suspect the IC is faulty.
Any comments?
Les.

[ANDRASONI]

Try to enter in "service mode"(press VOL-and INPUT or AV,after VOL- and CH-) an RESET the "lamp counter error".Exit service mode: unplugged the AC power cord and  wait 30 sec.Success, from Romania, all the best!

[In_Focus]

Over the weekend, I found a few minutes to get the inverter board on the bench, with ONLY a 24v supply from the bench PSU. I am working on the assumption that it would perform OK for a few seconds. Nothing happened. Voltage at the inverter control IC (BD9883FV) pin 20, BUT no Vcc (REG) output at pin 19.
I may try putting +5v on 19 to see if anything happens, but I suspect the IC is faulty.
Any comments?
Les.

A 24V supply alone will not statup up the inverter, you will also need to feed 3.3V to pin 12 of CN7501.

[OldLes]

Thanks for that, I will try when I get a few spare minutes.
Les

[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