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

So with the the wire on Q7907, you get 5 volts on J7915. I can't see what would be preventing the 5 volts for the panel from turning on, Try disconnecting the LVDS cable going to the t-con board, then with plug PE re-connected see if you get 5 volts on J7915

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

which is the LDVS cable? The 2 ribbons at the top of the board or those at the bottom behind the cage.?
Also, not familiar with those connectors. How do they separate?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

The lvds cable is the one between the main board and the t-con board, it must be behind shield, It is the wide 30 pin, You can also just unplug it from the main board.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

both sides behind the cage.
Ov.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

Hi R_J. I realize you're prolly have other things going, but when you get a chance.
Thanks,

Fritz

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

both sides behind the cage.
Ov.

Remove the shield to gain access to the t-con board.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

zero volts on J7915 with plug PE restored and the lvds unplugged.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

zero volts on J7915 with plug PE restored and the lvds unplugged.

That eliminates the t-con/panel, killing the voltage. Look for IC2007 on the main board, this is the ic that controls the PNL5V_ON, I was going to say post the voltages of the 5 pins, but it seems to be a bga chip.
So check the voltage on R2004 and C2024

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

IC2007, R2004 and C2024 seem to be on the B-side (trace).
Are there test points on top I can access?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

IC2007, R2004 and C2024 seem to be on the B-side (trace).
Are there test points on top I can access?

If you look at the service manual, it has board views, you would need to follow the trace and see where it appears on the other side.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

trying to figure out the location.
Is there any indication in the SM pcb drawings that would indicate this heat sink. The ref point might help localize the chip.


Or remove it that I might have a look at whats hidden.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

IC2007 pin1 is the PNL5V_ON_CPU and connects to [Y23] under the CPU.
IC2007 pin2 is the PNL_POW and connects to pin 63 of IC2002
Pins 1 AND 2 need to be high (3.3v) to get the PNL5V_ON (IC2007 pin4) to be high which turns on the panel power on the power supply.
Since the pins are hard to access I don't know how to check their voltages.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

Since I'm sure the PS is the problem, as when I swapped supplies with another of the same TV, it works.
Isn't there some point to source the problem on the power board?

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Since I'm sure the PS is the problem, as when I swapped supplies with another of the same TV, it works.
Isn't there some point to source the problem on the power board?

What voltages are missing on the power board?

PE
pin1=UR6V
pin2=gnd
pin3=PNL5V
pin4=PNL5V
pin5=gnd
pin6=gnd
pin7=UR10V
pin8=UR10V
pin9=gnd
pin10=gnd
pin11=UR13V
pin12=UR13V

PD
pin1=PS-ON
pin2=AC_DET
pin3=gnd
pin4=PNL POW
pin5=BU5V
pin6=gnd

LA
pin1~5=24V
pin6~10=gnd

If the only voltage you are missing is on plug PE: PNL5V , short Q7907 collector to ground, this will turn on the PNL5V and the tv should work. If it does, the Q7907 could be bad.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

PE
pin1=UR6V - 5.77
pin2=gnd
pin3=PNL5V - 0
pin4=PNL5V - 0
pin5=gnd
pin6=gnd
pin7=UR10V - 10
pin8=UR10V - 10
pin9=gnd
pin10=gnd
pin11=UR13V - 12
pin12=UR13V - 12

PD
pin1=PS-ON - 3.02
pin2=AC_DET - 3.07
pin3=gnd
pin4=PNL POW - 0
pin5=BU5V - 5
pin6=gnd

LA
pin1~5=24V yes
pin6~10=gnd


when I short Q7907 collector to ground, the red LED annunciators on the Main panel under the heat sink/cage, go off.
But the TV does not come on.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

The ONLY voltage that is not being supplied by the power supply is the switched PNL5V. This voltage comes directly from the working BU5V. The only control line for this voltage is PNL POW, It needs to be at 3.3 volts to turn on Q7907 base.
Shorting Q7907 collector to ground will force the PNL5V ON. So if the main board etc. are ok, the tv should work.

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

"Shorting Q7907 collector to ground will force the PNL5V ON. "

Something has changed here. The blue power LED upfront no longer lights.
I just shorted the C of Q7907 to gnd. PNL POW (P4 of PD) OV.
P3/4 of PE at 0V.


Perhaps Q7907 was failing or am I coming to the wrong conclusion?

Other Voltages are all still correct.

[R_J]

Re: sharp lc32d42u power supply - DPS-178APA

Disconnect the power supply from the main board and get two 1K resistors, Connect one resistor between BU5V and PS-ON and the other resistor between BU5V and PNL POW
Then check if you have all the voltages including PE pin 3,4 PNL5V

[metropical]

Re: sharp lc32d42u power supply - DPS-178APA

"Since all the other voltages are being supplied by the power supply, and you say the rest of the tv is working and the fault is on THIS power supply. Simply forcing on Q7926 will not be an issue and the tv will work because you tested proved it with the other power supply correct?

Correct.

Can I assume that this resistor test can be done without the "load" of the rest of the TV?
If so, I'd bring it to my friends shop week after next and do it there.
If not I'll get a couple 1ks from him and do under load.

But thanks so far, R_J, and I'll be in touch after I visit his shop.