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

[R_J]

Originally Posted by romasik

transformer T7901 ? Why 4,5 ?

WHY? because if that feedback winding is open circuit you will not get the boosted vcc voltage to make the ic work.
Look at the schematic, It's pins for this winding are 1&4, on your board they are 5&4, pin 4 is ground, pin 5 connects to D7906 and the 3 parallel resistors

[romasik]

[QUOTE=R_J;1134903]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

7909 not prsent on my board . R7908,R7909,R7913,D7904 checked all ok. but if 4,5 on transformer T7901 then his open.

[romasik]

Originally Posted by R_J

WHY? because if that feedback winding is open circuit you will not get the boosted vcc voltage to make the ic work.
Look at the schematic, It's pins for this winding are 1&4, on your board they are 5&4, pin 4 is ground, pin 5 connects to D7906 and the 3 parallel resistors

No the transformer is connected as in the schematic.

[R_J]

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[R_J]

Originally Posted by romasik

No the transformer is connected as in the schematic.

Your board is different from the DPS-167CP I was using Your board is a DPS-162KP, I was going by the original post title

[romasik]

20220521_004609.jpg

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20220521_004715.jpg

[romasik]

Originally Posted by R_J

Your board is different from the DPS-167CP I was using Your board is a DPS-162KP

I know I wrote about it at the beginning

[romasik]

So which pin on T7901transformer to check? may be 1,4 ?

[R_J]

Yes, check pins 1 & 4
The vcc voltage is initially supplied by the ic's internal startup cell which is bout 9volts, that part of the ic is working. When the power is first applied the internal mosfet should pulse the primary of T7901, this will induce voltage in the secondary winding and also the feedback winding, This will charge C7907 above 15 volts and the ic will stay operating, However the secondary voltage (5V) from D7950 must be regulated, so the optocoupler is used to control this voltage. The fact this feedback voltage is 40mV it is shutting down the ic.

[romasik]

on my T7901 1,4 - 0,5ohm, 2,3 - 3 ohm , 5,7 - 0,2 ohm

[R_J]

Originally Posted by romasik

on my T7901 1,4 - 0,5ohm, 2,3 - 3 ohm , 5,7 - 0,2 ohm

Yes it is good

[dskall]

Originally Posted by romasik

R7900 is ok, I am writing about C7900

You say things are good. Most fixed their problem with just a couple of component changes. How do we know you didn't replace a 2.2ohm with a 220 ohm?

[romasik]

Originally Posted by dskall

You say things are good. Most fixed their problem with just a couple of component changes. How do we know you didn't replace a 2.2ohm with a 220 ohm?

2.2 ohm red red gold gold
20220521_012804.jpg

[romasik]

Originally Posted by R_J

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.

PC7903, PC7904 i desordered for check . PC7904 need soldered back? Disconnect D7908 and power on board for check 3,4 pin on ic7903 ?

[R_J]

PC7904 is used to turn on Q7902 to supply vcc_on so it can be left out of circuit for now.
If you also remove pc7903 and D7908, pin 4 of ic7903 should be about 7volts, If it does not come up, try isolating just pin4 from the circuit trace, this will eliminate any other component on that line as well.

[Diah]

finally i saw now he post photos on his PCB.. i were wondering how other write parts No. and there was different model threats..
any way.. you don't have 5 V STB and PFC remain not active..
how are you testing. i cant find you wrote about.. where are the signal we are going to let PFC go high ?? this is not only Hot area work.. its cold area too.. beside i can see your soldering work the most worst i can see.. each part you took it out. you need to recheck the green line print chart 1000000000% you did break the line

[lotas]

Remove this supervisor IC7902, it sometimes brings problems with starting (the power supply works without it).

[romasik]

Originally Posted by R_J

PC7904 is used to turn on Q7902 to supply vcc_on so it can be left out of circuit for now.
If you also remove pc7903 and D7908, pin 4 of ic7903 should be about 7volts, If it does not come up, try isolating just pin4 from the circuit trace, this will eliminate any other component on that line as well.

I check without pin 4 0V, I bought another a6069h today and soldered it in, but nothing has changed on 4 pin 45mV on pin 5 9,5V

[romasik]

Originally Posted by lotas

Remove this supervisor IC7902, it sometimes brings problems with starting (the power supply works without it).

Possible unsolder resistor on pin Vcc for off power supervisor? It's enough?

[lotas]

Try like this.