Sharp LC-80LE757U - Click - shuts off

[budwich]

Re: Sharp LC-80LE757U - Click - shuts off

Thanks budwich :-)
I couldn't really spot any differences worth nothing. resistors are off, some higher, some lower by 1% or so. TV is awesome!

OK... but that was "examples" of things to look at... note the "strategic"... this means also some pins on "other components", etc such that you aren't really measuring a specific component but more a "path" or an "integrate circuit part".

Once you kind of have a "bench mark", then try heating the "old board" and do some similar measurements and see what / anything changes / jumps out at you. Similar you can freeze things and do that.

Further as others suggested, possibly a crack / poor solder so it will vital that you don't always directly measure at the component "pin" but at a place in a track that you can trace back to the component which then somewhat checks some poor path connections.

the "bench powering" testing that you may try to setup is also good but it depends on how much "support circuits" you need to rig up to get some form of "test bed". I suspect just "turning on" the board via power input and providing a couple of "states" (ie. ps-on, others) might not do much but maybe others will provide better "test bed experience".

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

I touched up the path of the AC_DET on all soldering joints.. board looks really good, so nothing seems broken / cold joint or anything of that nature.

Traced the AC_DET to a FET (PNP) and then opto. Seems the opto is getting the 4.9 one side of the BJT but somehow is not conducting when the TV tries to turn the power on. On the good board, the FET has 4.9 on one leg and it conducts to the other leg when the set is on (FET on) I replaced the FET thinking it must be it, but that didn't do it either!

I had to "Zip up" the TV unfortunately as I need to get rid of it (taking up my whole work area).. I would love to turn on this power board and attempt a repair instead of trashing it. If anyone has experience with what needs to be pulled up (connected) on the Main board connector so I can turn all the rails on and attempt bench-repair that would be great

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Guess you could test your old optos and the new optos and see what's up, there's one example of testing. https://cdn.badcaps-static.com/pdfs/...2a799f3264.pdf

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Pull the data sheet on your optos, might be testing method there too.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Old Part is labeled "R 2651B" and that's exactly what I got. The one I ordered has "NEC 2651B" Looking online, seems like multiple manufacturers make the part.

I'm trying to see when the power supply turns on does it actually send enough current through the opto to turn the BJT on? For that I need to turn the power supply on.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Guess you jump ps-on and standby pins with a resistor for safety to turn on powerboard without mainboard hooked up.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Yeah, see.. that's what I thought.. but when I connect PS_ON, PNL_POW to STB, I don't hear the relay click on / off like it does in the set.

[budm]

Re: Sharp LC-80LE757U - Click - shuts off

STB is the control signal pin NOT Standby power supply pin, BU5V is the 5V Standby power supply, that is why it did not work.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Thanks budm for clarification.

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Thank you! let me give that a shot.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Any progress?

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Hi nomoresonys,
Sorry no update yet, I'll work on it this weekend. I have a couple of other TVs that I need to finish by Saturday for Superbowl.
Thanks for checking back!

[ljintexas]

Re: Sharp LC-80LE757U - Click - shuts off

I bet its a crack in a solder joint..resolder

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

So it WASN'T the optos, did you make any progress or give up? was hoping to see a solution.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Any feedback on this?

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

Hi there,
My apologies for the long delay. I bought 3 Opto isolators from Mouser.com. I replaced all 3 optos on the board and no improvement. I really was only looking at AC_Det line. It so happened that "All 3 of these Optos" were defective; odd? i came across some of these parts by accident and decided to replace them again on the board and the issue seem to be gone. I know before the replacement the issue was intermittent, so maybe this is too soon. I'll wait few more days and few power cycles before I declare the solution.. just a quick update.
Thank you for the help.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

So if I read it right, all 3 of the replacement optos you bought were defective, you put in different ones and tv works?

[jason123]

Re: Sharp LC-80LE757U - Click - shuts off

that's what it seems like as of now. I don't know what the other 2 Optos do to be honest, but I know the AC_DET wasn't fixed the first time I installed the first opto. Replaced all 3 again, and it works perfectly now.. fingers crossed.

[nomoresonys]

Re: Sharp LC-80LE757U - Click - shuts off

Ok, thanks, hate it when I get a brand new part and it's defective before I even put it in. Done it a few times, then went chasing everything else before realizing they sent me a bad one, so exasperating.

[budm]

Re: Sharp LC-80LE757U - Click - shuts off

that's what it seems like as of now. I don't know what the other 2 Optos do to be honest, but I know the AC_DET wasn't fixed the first time I installed the first opto. Replaced all 3 again, and it works perfectly now.. fingers crossed.

Glad to hear the TV is fixed.
Are the Opto from EBAY or from Mouser/Digikey?