Sharp LCD TV Blows Fuses LC-19SB24U

[Solder Boy]

I've had this unit on the shelf for a year so I dusted it off to see what was wrong with it. It didn't turn on at all. I checked the alum caps they were good but I'm not sure about the two rectangular black caps.

One is .1uf 275v the other is .22uf 275v. The one black cap doesn't even register anything on my ESR meter and the other one reads 25 and is in the yellow zone.

The small black fuse is a replacement.. it blew when power was applied.

Would I be in the right area if I suspect those two black caps are bad?

The grey fuse tested ok.

[retiredcaps]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

It didn't turn on at all.

The small black fuse is a replacement.. it blew when power was applied.

Would I be in the right area if I suspect those two black caps are bad?

The grey fuse tested ok.

I haven't worked on any LCD TVs, but people report that these types of caps rarely fail.

If the fuse blew, I would check the bridge rectifier (D7527) for shorts. Number the pins 1-4. Set your multimeter on 200 ohm (if manual). With power off and lcd unplugged, measure 1-2, 1-3, 1-4, 2-3, 2-4, and 3-4. Any reading below 30 ohms suggest a shorted bridge rectifier.

If there are no shorts, check capacitor C7528 to see if you get mains voltage x 1.4 DC V. That is 120 AC * 1.4 = 160 to 165V DC.

If that is present, there seems to be two diodes mounted on heatsinks. Using a ground screw for the black probe, put the red probe on the middle pin and measure the DC V.

[Hobby 1]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

Its not a cap, its the power FET. Look for one with a dead short across the legs. Replace it with a higher rated one. These are all failing with the same problem. Takes longer to open the case than to fix it.

[Dgtech]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

I've had this unit on the shelf for a year so I dusted it off to see what was wrong with it. It didn't turn on at all. I checked the alum caps they were good but I'm not sure about the two rectangular black caps.

One is .1uf 275v the other is .22uf 275v. The one black cap doesn't even register anything on my ESR meter and the other one reads 25 and is in the yellow zone.

The small black fuse is a replacement.. it blew when power was applied.

Would I be in the right area if I suspect those two black caps are bad?

The grey fuse tested ok.

It sounds to me like you have a direct short to ground on the primary (HOT) side. This should be easy to find. You can do everything with the power off. First, measure across the fuse with ohm meter. What resistance do you get there. If zero, then I'd desolder the rectifier, and then re-measure.

[easterbran]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

Sorry to resurrect such an old thread. I am currently having the same issue with my LC-19SB24U. I have tested both F7501 (good) and F7502 (bad). So I replaced F7502 with a 2.5A 250V slow-blow fuse. Every time I connect the Power Supply Board to the wall, the F7502 fuse immediately blows. This happens with the Power Supply Board isolated from all other components (not connected to the main board or backlights).

I then checked the two large diodes (D7520 and D7526) for continuity from anode to cathode and they looked good. No continuity in the reverse direction, as expected. These were both tested off of the board.

All caps appear to be in good shape, no bulging or discoloration. Following the advice in this thread, I looked into the FETs attached to the heatsinks. Following this guide (http://electronicsbeliever.com/how-t...-is-defective/), I found that the resistance was nearly zero across all pins of Q7523, which is part number (FQPF8N60C), and that this likely means that this transistor is bad. The other FET showed high resistance (order of kOhms) between all pins, so I ruled this one out.

I'm currently waiting for the new FET to arrive, but was wondering if anyone had any advice or things to check in the meantime?

I'm referencing the Troubleshooting diagram (attached) from the service manual (downloadable here: ).

[easterbran]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

Forgot to mention, I have checked the D7527 Bridge Rectifier to make sure the resistance is appropriate from anode to cathode of each diode, and all 4 pins looked good. This was done with the rectifier off the board.

[R_J]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

If the fet is shorted all around, then it is very likely components in the gate drive are also bad and need to be checked.
Check D7522 (15volt zener) Q7524 (2sc2712)

[TechGeek]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

Is it a Hot to Neutral or Hot to Ground short? You can verify this by checking resistance on the 3 pin IEC connector. Ground is the lonely pin.
Hot is on the left if the connector looks like this:
|
| |

Hot on right:
| |
|

EDIT: the lonely pin is on the middle

[easterbran]

Re: Sharp LCD TV Blows Fuses LC-19SB24U

SOLVED!

It was indeed the Q7523 FET, which is part number (FQPF8N60C). I replaced it with a $10 replacement off eBay, and all is well. No more blowing the F7502 fuse and the monitor works as usual.

Thanks all!