sharp lc32d42u power supply - DPS-178APA

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

Took some doing but there is always a piece of sacrificial Cat 5.

I took a piece of wire from ground to the Q7907 collector.
With TV on or off, 5v.

So Q7926 is good?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Use a piece of wire to connect the emitter to collector, There is only about 5 volts at those points, or take a piece of wire from ground to the Q7907 collector, that will also turn on Q7926

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

I'll have to find me some better gator clips. It's pretty tiny on that Q.
But, unplug PE on the power supply and with the tv on, check the voltage on J7915. It is 0 volts.

This might take me a few days to find leads out here in the boonies.
Prolly pick some up in the city next week.
I'll be in touch.
Thanks very.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

1.923k Ω

Ok good, so the PNL5V line is not shorted. Unplug PE on the power supply and with the tv on, check the voltage on J7915. If it is 0 volts, short the emitter and collector of Q7907 (the two outside legs) together and see if you get +5v on J7915. this will check if Q7926 is working.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

1.923k Ω

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

OK. Will do.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

I don't have a schematic, The main board does have panel 5 volt detect line, It is possible that Q7907 or Q7905 are bad, And the main board is not seeing the PNL5V
Since you are sure the fault is on the power supply, The other problem could be that some thing like C7922 is shorted, check the resistance from J7915 to ground

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

Even if the cap was shorted, the voltage drop across R7930 should not totaly kill the 3.3volt pnl pow control signal

perhaps that accounts for post 25 above?
I don't suppose you could post the schematic?
It'd be useful to me to know what I'm looking at.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

I see now that C7921 is a surface mount on the under side of the board.

Even if the cap was shorted, the voltage drop across R7930 should not totaly kill the 3.3volt pnl pow control signal

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

I see now that C7921 is a surface mount on the under side of the board.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

All you need to do is lift one end of R7930, If THEN the voltage on PD,pin4 comes up, you might have a shorted component but I doubt that is the issue.

Can that be done with the power board out of the TV, or does it need to be done under "load"?

If that isn't the issue, what might other possibilities be?

I would think it's the power board, as, like I said, I swapped supplies with another of the same and the other TV that was dead was fine.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Thanks very. R_J.

I do hear noise from the speakers.
So change out both C7921 & Q7907? If I can find C7921.
Is it a small or large cap?

All you need to do is lift one end of R7930, If THEN the voltage on PD,pin4 comes up, you might have a shorted component but I doubt that is the issue.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

Thanks very. R_J.

I do hear noise from the speakers.
So change out both C7921 & Q7907? If I can find C7921.
Is it a small or large cap?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

The service manual does not have the power supply schematic.

Even If you don't have the panel 5 volts, the tv should work, you just won't have an image because all that would be missing is the +5 volts for the tcon and the panel. (SM page 49)
Post #19 has pictures of this part of the circuit board
Since you have BU5V, UR13 & UR10V I would say your power supply board is working properly.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

I have UR13v PE, pins 11,12 showing 12v.
UR10v pins 8,7 is good.
Funny, my SM doesn't even list Q7907 or C7921. But I did find Q7907 on the PCB.
Ah, I see, my book doesn't have the PS parts list .... near as I can tell
Can it be checked in circuit or only lifted?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Do you have UR13v PE, pins 11,12 and UR10v 8,7 ?
If the PNL_POW signal is being killed, there are only 2 components that will do that, either C7921 or Q7907 are shorted to ground
Best I can do with paint, but this is the circuit

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

OK. But as I said. 2 of the same TV. Swapped out the PS board and all is well.
.
Something else occurs to me. That voltage, Pin4 on plug PD, isn't steady 0v. It jumps around too fast to see the top, stand-by or powered.
Unlike the 5v pin which is quite steady.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Then the main board is not sending the PNL_POW signal

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

yes. all boards connected

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

guess I missed RJs post.
In any case, Pin 4 of Plug PD stays at 0v, in stand by or powered on.
Same with Pin 3 on plug PE, 0v, in stand by or powered on.

Is the main board connected?