Sharp LC-52SB55U (No Power)

[ddjmagic]

Hi all, I'm looking for some help with Sharp LC-52SB55U.

It's a US model, but currently being used in the UK for a few years (TV is 100-240V Power)

Currently the TV does not power on, no lights or noises when the power button is pressed.

I was not present when the TV stopped working but apparantly the TV randomly 'clicked' a few times while the green light came on and off a few times, since that it hasn't powered on or shown any lights.

I have taken the TV apart and the power board is RDENCA295WJQZ (DPS-277BP)

I've checked for voltage on the PD connector and there is 0v on any of the pins (including the one marked BU5V)

I've confirmed power is getting to the board, and the main bridge rectifier (D15XB60) has 240V AC and 300V+ DC.

I can't seem to find any schematic for the power board, so a bit stuck on trying to find the issue.

Any help or advice to troubleshoot further is appreciated.

Thanks, Dan.

[lotas]

Re: Sharp LC-52SB55U (No Power)

Dps-277bp

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

Dps-277bp

Great, thank you. I'll have a look through that.
Anyone know of any common problems/most likely issue on this board?

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

The last place I seem to be finding any DC voltage is diode on the center of the board (D7908).

I've checked D7908 & D7909 (next to it) in circuit and both are showing very low resistance in both directions (0.02), other diodes I can see test 0.6 & OL, so potentially D7908/D7909 diodes could be the issue?

Would the next step be taking them out of the circuit and test again?

[dick_barton]

Re: Sharp LC-52SB55U (No Power)

Would the next step be taking them out of the circuit and test again?

That would be a better way of being certain if one or both are faulty.

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

That would be a better way of being certain if one or both are faulty.

Thanks. D7909 tests fine off the board but D7908 is still testing bad off circuit.
D7909 test good back on the board. So it seems that D7908 diode is no good.

Does anyone know where in the UK something like this could be purchased?
Could potentially something else have casued the bad diode?

[lotas]

Re: Sharp LC-52SB55U (No Power)

Thanks. D7909 tests fine off the board but D7908 is still testing bad off circuit.
D7909 test good back on the board. So it seems that D7908 diode is no good.

Does anyone know where in the UK something like this could be purchased?
Could potentially something else have casued the bad diode?

Look for this name of the Zener diode D7908 - 1N5383BRLG.

[R_J]

Re: Sharp LC-52SB55U (No Power)

D7908 usually checks open and will be ok it is a high voltage tvs diode. In circuit, the transformer primary is across the diodes.
Check that R7914 is ok,
Check the voltage across C7918 and C7915, it could be that both caps are bad and not letting the standby power supply section run. These caps can go open.

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

D7908 usually checks open and will be ok it is a high voltage tvs diode. In circuit, the transformer primary is across the diodes.
Check that R7914 is ok,
Check the voltage across C7918 and C7915, it could be that both caps are bad and not letting the standby power supply section run. These caps can go open.

D7908 seems to be showing a short on the tests? Unless I'm reading the meter wrong (also has continuity both ways)

R7914 seems to test all good, there is no voltage at C7918 or C7915 at all.

[R_J]

Re: Sharp LC-52SB55U (No Power)

If D7908 checks shorted, then it is bad. Try replacing it and see if the circuit operates. The fact that it is shorted basically across the transformer primary would cause the circuit not to function.

[lotas]

Re: Sharp LC-52SB55U (No Power)

This is a protective diode, to check the power supply, you can turn it on without it, if everything starts, then the problem was only in it.

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

This is a protective diode, to check the power supply, you can turn it on without it, if everything starts, then the problem was only in it.

Thanks for this. I can confirm with everything back together except D7908, everything operates and powers up correctly.

I just need to find a replacement diode now and I think I'll be good to go.

Thanks everyone for the help.

[lotas]

Re: Sharp LC-52SB55U (No Power)

1N5383B - Zener Single Diode, 150 V, 5 W

[ddjmagic]

Re: Sharp LC-52SB55U (No Power)

1N5383B - Zener Single Diode, 150 V, 5 W

I managed to source this diode, soldered it back in and TV is all back together now and working great

Thanks again.