Sharp LC-52D64U hard to start

[Dannyx]

Re: Sharp LC-52D64U hard to start

Bypassing the protection on the inverter IC sounds like the only option left to mess around with at this point.

[nomoresonys]

Re: Sharp LC-52D64U hard to start

Wonder if there's a way to test the transformers on inverter, it doesn't look as easy to do as on some samsung tvs?

[elitegroups]

Re: Sharp LC-52D64U hard to start

Thanks, a lot of good info in that video. I touched up all the solder joints of the transformers but didn't help. I was trying to zone in on the individual component that needed to heat up in order for the tv to fire up but I noticed if if heated up the bare sheet metal section next to the master inverter the set was firing up immediately as well. So it seems the hair dryer is heating up the tubes just behind which is the absolute worst case scenario. The set seems like a good candidate for an LED conversion! I saw a video on youtube where a guy converted 42" version but I have to figure out how get to the tubes without destroying the lcd.

https://www.youtube.com/watch?v=jdk-GxU7TU4

Please disregard, I tried heating up the sheet metal again but no go, it is something on the master inverter that is thermal related. I wil try to test the transformers. One has a slight bulge in it.

[Dannyx]

Re: Sharp LC-52D64U hard to start

Can you hear any arcing ? I had the same issue with a Panasonic (I think) which used this master-slave inverter setup and although not visible, one of the transformers was arcing internally. It was just barely audible if I placed my ear on it, so I took the gamble and bought the two inverter boards and swapping the master one did fix the issue. If you can get them for a good price, it might be worth doing the same, instead of bothering to track down the issue and fix it at component level. True, it's more "fun" this way for us tech geeks

[nomoresonys]

Re: Sharp LC-52D64U hard to start

Ok, so if I'm understanding, you narrowed it down to 1 inverter board and tv is still coming on as soon as you hit it with the heat?

[Dannyx]

Re: Sharp LC-52D64U hard to start

Well if heating the board causes it to turn on, I'd try to zone in on the problematic area by heating less and less of the board until you pinpoint it. I did this with a mainboard once which had a bad cap somewhere but there were a lot of them clustered together, so identifying the bad one proved difficult. I used the smallest nozzle of my hot air station and began heating each one gently and trying out the TV each time until I found the bad one.

[nomoresonys]

Re: Sharp LC-52D64U hard to start

Good idea Danny, I think I would try grabbing an inverter too, can probably get one for 10-20 bucks or less, shopjimmy list here, looks like theyre sold out, might show some substitute part numbers tho: https://www.shopjimmy.com/catalogsea...?q=+LC-52D64U+

[elitegroups]

Re: Sharp LC-52D64U hard to start

Great advice guys! I think i have it narrowed it down to a single mosfet now. I touched up the joints but no go. I made a funnel for the hair dryer and found it this way. I can remedy the the problem on command now by heating the fet and quickly induce the problem by cooling it. Im going to swap its position with another of the same fet on the board and see if the trouble moves with it.

[nomoresonys]

Re: Sharp LC-52D64U hard to start

Nice work, looks like you found the culprit.

[elitegroups]

Re: Sharp LC-52D64U hard to start

So I swapped the suspect mosfet positions with another on the same board but the trouble didn't follow the suspected fet. So it looks now the issue is not the fet but the actual board being heat up. The pad area underneath the problem area looks darkened from prolonged heat and I noticed a very small hairline crack on the top side of the board underneath where the fet was. Now this is the trouble area and heating it up temporarily fixes the issue. I was hoping to find a broken trace or solder joint on the flip side but couldn't find any defects. There is an smd resistor and diode directly underneath where the fet was so I touched up the joints but no go. I did a lot of continuity tests on the traces and pads in the area as well but no improvement. I am uploading some pics of the area. One interesting thing I noticed is when the area is cold and I fire up the set while holding the fet, the screen flickers as usual and you can immediately feel the fet heat up a great amount. Now if I heat up the board with the hair dryer then turn it on the screen comes on immediately no flickering and the fet doesn't get very hot.

[Dannyx]

Re: Sharp LC-52D64U hard to start

I would continue reflowing stuff in that area. Another idea that just crossed my mind is to see what transformer that FET is driving and swap THAT with another one, rather than the FET. The heat might cause some strange behaviour in the nearby transformer as well Though you said you tried funneling the heat as much as possible, through conduction some of it may have "leaked" down to the transformer...just my 2 cents at this point.

[budwich]

Re: Sharp LC-52D64U hard to start

you appear to have narrowed down the area of focus. You have looked at what happens in terms visual and "touchy / feely" observations.... but now you need to also check the voltages that are appearing at that component during your two different scenarios to see if its a gate or "switch issue". As suggested, perhaps its another component that is causing the draw thru the "switch".

one other point.... you have been working on the "premise" that heating is helping with "connectivity" but based on your recent observation (device heating up when "cold started") appears to indicate that may there is a some form of "short" connection when cold that is causing a large draw heating up the device but when the "area" is pre-heated, that "short connection" is broken... potentially by things like board expansion. Maybe check various resistance paths at "cold" and at "hot" to see if anything jumps out.

[elitegroups]

Re: Sharp LC-52D64U hard to start

Those are some good tips to narrow it down. Im going to have another go at it today. Just wondering, does this seem like the trouble could be a bad lamp and the heavy current draw is from the fet and transformer trying to fire up the faulty bulb?

[budwich]

Re: Sharp LC-52D64U hard to start

yep.... just like a regular house tube, if it takes quite a bit to start / if it is "burned" and take a bit to "arc up" then it is hard on the "ballast" and will usually / eventually take out the ballast.

[elitegroups]

Re: Sharp LC-52D64U hard to start

Great News! The set is working now. I had to bite the bullet and buy the master inverter board and all looks ok now. It would of been nice to fix the old board but now I have some spare transformers in case of future troubles.
What led me to throw in the towel was while trying to measure the gate voltages to the mosfets to see if one wasn't receiving a proper gate voltage to fire, my probe slipped and shorted one FET out. So now my trouble was compounded and i just decided to get the whole board. However I was getting some measurements i didn't understand. There are 8 mosfets on the board, 4 p-channels and 4 n-channels. Now on the n-channel fets i got a reading of around 4.5vdc from gate to chassis but on the p-channels I measured 60vdc on their gates which seemed too high. 60 volts also happens to be the supply voltage to the board. I know a scope is really needed to see the waveform but I wonder if this is some sort of push-pull configuration how the fets are arranged. A big thank you to the great tips and help!