Sharp LC-60SQ15U TV DPS-167CP - No power

[R_J]

Originally Posted by romasik

7907 check his ok, on 4 legs 40mV

Check for a shorted D7988, or defective PC7903, something is killing the feedback voltage. I suspect the voltage needs to be above 1 volt and maybe around 3~5 volts, but needs to be lower than 8 volts

[romasik]

Originally Posted by R_J

Check for a shorted D7988, or defective PC7903, something is killing the feedback voltage. I suspect the voltage needs to be above 1 volt and maybe around 3~5 volts, but needs to be lower than 8 volts

D7908 170 and 90 Omh

[romasik]

What do you think?

[R_J]

Originally Posted by romasik

What do you think?

I think something is causing the voltage to be too low. If you look at the datasheet for the ic (page 11) you will see FB/OLP pin is supplied by approximately 7 volts, this line is controlled externally, so I suspect either the diode D7908 is bad or the optocoupler is bad.
170Ω and 90Ω does seem to be low. lift one end of the diode and check again to see what the resistance is.

[romasik]

Originally Posted by R_J

I think something is causing the voltage to be too low. If you look at the datasheet for the ic (page 11) you will see FB/OLP pin is supplied by approximately 7 volts, this line is controlled externally, so I suspect either the diode D7908 is bad or the optocoupler is bad.
170Ω and 90Ω does seem to be low. lift one end of the diode and check again to see what the resistance is.

Ok, i check later (it's too late, I'm going to sleep). How i can check IC7903 defective or not?

[R_J]

Originally Posted by romasik

Ok, i check later (it's too late, I'm going to sleep). How i can check IC7903 defective or not?

I would check the resistance and compare with the other two or try exchanging it with pc7904 and see if you get your standby voltage.
You should be able to leave the zener diode out of circuit for testing.

[romasik]

Originally Posted by R_J

I would check the resistance and compare with the other two or try exchanging it with pc7904 and see if you get your standby voltage.
You should be able to leave the zener diode out of circuit for testing.

What is PC7904 ? And which diode should be soldered to test?

[romasik]

Originally Posted by romasik

What is PC7904 ? And which diode should be soldered to test?

PC7904 i found, how check his?

[romasik]

I checked diode D7908 57Omh and infinity , PC7904, PC7903 desolder and check all fine(

[R_J]

If the optocoupler and the diode are good, then it only leaves the ic that is bad.
If you look at the datasheet page 11, you will see that without anything connected to the FB pin, that pin should be at 7 volts. Normally the optocoupler controls this voltage and varies it around 3~4 volts to control the ic. You measured almost 0 volts on the FB pin. So something is keeping the voltage low or the ic is bad.

[romasik]

Originally Posted by R_J

If the optocoupler and the diode are good, then it only leaves the ic that is bad.
If you look at the datasheet page 11, you will see that without anything connected to the FB pin, that pin should be at 7 volts. Normally the optocoupler controls this voltage and varies it around 3~4 volts to control the ic. You measured almost 0 volts on the FB pin. So something is keeping the voltage low or the ic is bad.

is it possible to check ic somehow? in my city they are only in one store, it will be from the same batch.

How i can check my ic? Thanks

[romasik]

and I also suspect the C7900, but I don’t understand how to check it with a multimeter. Like a regular cap, it does not show voltage after charging.

[dskall]

What is your ohm reading on R7900?

[romasik]

Originally Posted by dskall

What is your ohm reading on R7900?

R7900 is ok, I am writing about C7900

[R_J]

C7900 is likely good, If it was open circuit it will not stop the circuit from working. This cap is not your problem.

[romasik]

I no longer know what to do, maybe IC7903 is defective ? I also read on another forum that the voltage on large caps should be 380V with a working ic7801, and I have 300

[R_J]

Originally Posted by romasik

I no longer know what to do, maybe IC7903 is defective ? I also read on another forum that the voltage on large caps should be 380V with a working ic7801, and I have 300

You need the #$%%^ standby circuit working BEFORE the pfc circuit OR the main supply circuit will work.

[romasik]

Originally Posted by R_J

You need the #$%%^ standby circuit working BEFORE the pfc circuit OR the main supply circuit will work.

what to do? try to change IC7903 again?

[R_J]

Check the transformer winding between pins 4 and 5, it should be almost 0Ω, then check the resistors R7908,R7909,R7913, if they are good, check the diode D7904, also check the zener diode D7909

If these are all good, Disconnect D7908 and pins 3&4 of the optocoupler PC7903 and see if the voltage on pin 4 of ic7903 comes up to about 7 volts. If it does not, I suspect the ic is bad.
It is a simple circuit, and should not be that hard to diagnose.

If you look at the schematic for the dps-262, you will see the pfc ic ic7801 pin8 gets it's VCC_ON voltage from the emitter of Q7902, The collector voltage is supplied via D7906/C7918. This voltage is only there when the standby circuit is working.

[romasik]

Originally Posted by R_J

Check the transformer winding between pins 4 and 5, it should be almost 0Ω, then check the resistors R7908,R7909,R7913, if they are good, check the diode D7904, also check the zener diode D7909

If these are all good, Disconnect D7908 and pins 3&4 of the optocoupler PC7903 and see if the voltage on pin 4 of ic7903 comes up to about 7 volts. If it does not, I suspect the ic is bad.
It is a simple circuit, and should not be that hard to diagnose.

transformer T7901 ? Why 4,5 ?