Sharp LC-37D64U - no power

[eggo]

Hi

I am trying to troubleshoot a Sharp LC-37D64U that has no power. The part number of the power supply board is RDENCA257WJQZ. I suspect it is the diode that is in the red rectangle in the pic. The problem is that I cannot seem to cross reference the part number. It is D3S58 and the location on the board is D5701. Does anyone know what the equivalent part number is?

[budm]

Re: Sharp LC-37D64U - no power

You have TWO power supplies, the smaller transformer is for the always ON POWER SUPPLY, the large transformer is for switched power supply that will come on when PS-ON is present and standby power supply has to be working.
So you need to find out first if the standby power supply is working or not first.
We also need high res straight shot pictures of the whole top side and bottom side of the board.
Why do think that the diode is bad?
What Voltage checking have you done so far in the hot side and on the cold side?

[eggo]

Re: Sharp LC-37D64U - no power

I do not have any stand by power (measured across the zener for the power switch).
On the hot side, I have 346 VDC coming out of the bridge rectifier.
On the hot side of the small transformer, starting from the top down, I have 57.5 mV AC, 178 mV AC and 92 mV AC. On the cold side of the small transformer, I have 12.7 mV AC.

[budm]

Re: Sharp LC-37D64U - no power

Are you using the chassis as the reference GND for the meter wen you make the measurement in the hot side of the circuit? When working in the hot side you need to use the negative leg of the main filter cap as the GND ref. for your meter.
What is your country AC line Voltage?

[eggo]

Re: Sharp LC-37D64U - no power

Sorry wrong measurements
Starting at the top of the small transformer
68 V AC and 116.5 V DC
68 V AC and 289 V DC
92 mV AC and 0 V DC
The line voltage is 120 V AC

[budm]

Re: Sharp LC-37D64U - no power

Sorry wrong measurements
Starting at the top of the small transformer
68 V AC and 116.5 V DC
68 V AC and 289 V DC
92 mV AC and 0 V DC
The line voltage is 120 V AC

Your readings do not make any sense to me, you have 8 pins on the primary side of the transformer, 2 of them are not used.
https://www.badcaps.net/forum/attach...3&d=1539616261
D741 on the cold side of the transformer is the rectifier diode for the standby power supply, is it good?

[eggo]

Re: Sharp LC-37D64U - no power

That diagram was the one with the incorrect measurements and I was not able to delete it. Here is the correct one.
I pulled D741 and checked it with the diode test function on the multimeter and forward bas was 0.168 V and reverse bias was OL

[eggo]

Re: Sharp LC-37D64U - no power

Sorry the bottom 2 readings are 92 mV AC and 0 V DC and not 9.2 as shown in the pic

[R_J]

Re: Sharp LC-37D64U - no power

Check if you have standby voltage. Meter Black to chassis Meter red to D741 (white circle side of diode)
If you do not have standby, It is a good chance that IC721 is bad.
Check if F721 fuse is good also

[eggo]

Re: Sharp LC-37D64U - no power

I get 0.47 VDC at D741. I checked F721 and it is good. Is there a way to test IC721? I will see if I can pick one up locally on the weekend and change it