Sharp 56FW-53H Pincushion


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Sharp 56FW-53H Pincushion

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Wiz
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Sep 18, 2005, 2:16 PM

Post #1 of 14 (1747 views)
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Sharp 56FW-53H Pincushion	Can't Post

Hey, I have a sharp 28" TV that had both the LOPT and Chopper transistors blown. I replaced these, with similar transistors, although not exactly the same ones. The picture and sound work, however, the picture has a pincushion effect to it. Is this because the transistors are not correct, or could the be some other component that has gone. I couldnt see anything that had obviously blown, or anything that could have made the transistors die in the first place, but as the replacements havent died yet, I am assuming that it was a one off.

Any sugestions welcome.

Oliver

(This post was edited by Wiz on Oct 27, 2009, 5:39 PM)

rrobor
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Sep 19, 2005, 11:59 AM

Post #2 of 14 (1722 views)
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Re: [TheOW] Sharp TV Picture problem. [In reply to]	Can't Post

no it will be the pin correction gone, there will be a rransistor and a coil, often the coil goes shorted turns or may be the modulator diode. Fom the flyback transistor collector there is usually a feed via a diode to a coil, often Sharp use a non polar electrolytic at 4.7uf and thats always stuffed, and there will be a protection resistor.

Wiz
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Sep 19, 2005, 7:43 PM

Post #3 of 14 (1715 views)
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Re: [rrobor] Sharp TV Picture problem. [In reply to]	Can't Post

Not really sure where abouts this cap is, but to my new problem, The tv has a picture, but then when still plugged in, and the switch is turned off, there is a series of sparks from the board to both the live and neutral wire on the power yoke on the board. Please can anyone tell me why this should happen, I dont really want electricity sparking back into the mains. Could any of the transistors failing cause this problem?

Wiz
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Sep 19, 2005, 8:50 PM

Post #4 of 14 (1713 views)
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Re: [TheOW] Sharp TV Picture problem. [In reply to]	Can't Post

Update, The sparking is from around the main power switch going towards the mains lead from the board. I think that the high voltage that is causing the sparking when the switch is off is coming from the earthing on the back of the tube (this gives a zap if touched while sparking), in which case, I think that this high voltage is going straight back down the mains when the TV is on, and only sparking when off cos there no easy way for it to get out of the circuitry. This obviously shouldn't be happening, and as im not experienced enough, I don't know where to look for a problem.

Please Help

mel
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Sep 19, 2005, 9:51 PM

Post #5 of 14 (1710 views)
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Re: [TheOW] Sharp TV Picture problem. [In reply to]	Can't Post

Did you remember to reconnect the Dag shield wire to the chasis ground?

Wiz
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Sep 19, 2005, 11:00 PM

Post #6 of 14 (1706 views)
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Re: [mel] Sharp TV Picture problem. [In reply to]	Can't Post

There is a wire connecting the back of the tube to bothe the tube board and the main circuitry, these are both connected.

Wiz
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Sep 21, 2005, 11:23 PM

Post #7 of 14 (1695 views)
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Re: [TheOW] Sharp TV Picture problem. [In reply to]	Can't Post

The sparking is intermittent now, some times it does it, other times it doesnt???

The image is less pincussion like than it was before, after changing the chopper for another transistor. where abouts is the blown cap that rrobor mentioned likely to be?

rrobor
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Sep 22, 2005, 10:19 AM

Post #8 of 14 (1689 views)
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you have a power feed to the pin correction transistor it can be on that line, I dont know this set so i could be wrong.

Wiz
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Oct 27, 2009, 5:38 PM

Post #9 of 14 (1140 views)
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Re: [rrobor] Sharp TV Picture problem. [In reply to]	Can't Post

Well to bring up an old post, I've been at university for the past few years so this TV has sat in my room since then, still with the same problem.
Now I'm renting a flat, the 32" CRT I have that works, is too big so I'm using the sharp (56FW-53H) one.
After 4 years, Im hoping there might be some new members who know this set or existing members who now have experience of this set who can hopefully give me the solution to this problem.
Having not looked at the set in 4 years, I will go through it later to see if I had overlooked something previously.
Cheers,
Ollie

techchris
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Oct 27, 2009, 6:43 PM

Post #10 of 14 (1137 views)
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Re: [Wiz] Sharp TV Picture problem. [In reply to]	Can't Post

the usual problem on this model was a corrupted eeprom memory chip.You have to order a preprogrammed one from sharp or parts supplier

Wiz
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Oct 28, 2009, 12:14 AM

Post #11 of 14 (1129 views)
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Re: [techchris] Sharp TV Picture problem. [In reply to]	Can't Post

I will look into getting a replacement, whilst im looking into finding one, do you think having the 2 transistors I replaced slightly different from the ones that were removed would cause this problem?

Thanks,
Ollie

techchris
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Oct 28, 2009, 7:38 PM

Post #12 of 14 (1118 views)
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Re: [Wiz] Sharp TV Picture problem. [In reply to]	Can't Post

depends on what was swapped for what. hopefully both pnp or npn types and not reversed.

Wiz
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Oct 28, 2009, 10:31 PM

Post #13 of 14 (1116 views)
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Re: [techchris] Sharp TV Picture problem. [In reply to]	Can't Post

It was 4 years ago when I changed them, so Im not entirely sure what the originals were that I replaced. If I remember correctly, they were replaced with components from another 28" widescreen which had the cathode and grids shorted in the CRT. unsure of the make though.
I would imagine that the thing wouldn't work at all if I had put PNP in place of NPN, but I will find the schematic and check this evening.

Wiz
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Oct 31, 2009, 6:34 AM

Post #14 of 14 (1099 views)
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Re: [Wiz] Sharp TV Picture problem. [In reply to]	Can't Post

Found the component at fault.

After playing in service mode, I noticed that the horizontal sizing etc didn't do anything to change the picture. The horizontal shift moved the picture far enough that I could just see the edge of the picture and the pincushioned side. moving it vertically at this point showed the picture moving but not the pincushioned edge.
I concluded that the flyback transformer controlled horizontal windings must pull the picture electrons beyond the edge of the screen and the chip decided where to put the picture in that. Deciding I couldn't fix the chip, I hoped that there was a component faulty that was causing the magnets to pull the electrons too far and stretching the picture horizontally.
After some following the circuit with a multimeter, I found the fauly component.
It's a surface mount transistor (Q506 [2sd2391]) short across collector and emitter. This component appears to amplify the E/W output from the video processor chip, and therefore could easily cause the problems I've been having. Once I get a replacement I will hopefully have a fully working television again.

Are there any known problems which would cause this component to fail and is there anything else likely to have failed as a result?

BTW I'm not sure if my original post 4 years ago is talking about the same TV, fixing them is a hobby of mine, and I vaugely recall having 2 sharp TV's strangely it appears with a similar problem. As I found out, I haven't replaced any transistors in this particular one so it would appear that this surface mount transistor is the only fault I have found so far.

(This post was edited by Wiz on Oct 31, 2009, 8:18 AM)

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