Rca L40FHD41YX9 no power

[TimT]

something new every time I open a TV. This TV seems dead so I pulled the power supply and started testing. power connectors with 2 rows of pins are getting 12v each but the GND are also getting 12v..this dont seem right? also noticed some solder joints that are solder together at connectors.

[ben7]

Re: Rca L40FHD41YX9 no power

I'm not sure what pin your pointing out, but they all shouldn't read 12v. Are you using the DC setting on your DMM, and does it have a good battery?

[TimT]

Re: Rca L40FHD41YX9 no power

dont get the 12v at GND with board installed... mabe I should not be testing out of chassis?.. getting 5v SB to mainboard. no power at any other pins. no power to inverter.

[ben7]

Re: Rca L40FHD41YX9 no power

dont get the 12v at GND with board installed... mabe I should not be testing out of chassis?.. getting 5v SB to mainboard. no power at any other pins. no power to inverter.

You must be using the wrong reference point. Measure the voltage on the 12v rail, with the positive probe on the 12v pin, and the negative probe on one of the GND pins.

You say no power to any other pins, but, that seems right, since you haven't pressed the TV's power button to see if the other rails (especially the 24v one - for the backlights) jump a little. If they do, then that means there is a short and the TV cant turn on.

Also, what is the voltage on the 'BL-ON' pin? I believe that is the power-on pin.

[TimT]

Re: Rca L40FHD41YX9 no power

probe grounded to chassis bolt. removed connector from mainboard 5v SB is the only voltage at connector. don't know why I was getting 12v to ground out of chassis. ground probe was connected to screw in powerboard. but it's installed now, power putton does nothing.

[ben7]

Re: Rca L40FHD41YX9 no power

Can you carefully measure the voltages across these capacitors?

[TimT]

Re: Rca L40FHD41YX9 no power

Ben7 I am not really not sure how to do this? do I just touch the tops of caps with probe?

[selldoor]

Re: Rca L40FHD41YX9 no power

Ben7 I am not really not sure how to do this? do I just touch the tops of caps with probe?

No you need to find where the cap leg joints are on the bottom of the board and test there. Its not easy, as for the BIG cap it could be 400vDC.
You do need the board powered up - The smaller caps will be a max of 50vDC.
If you are using the boards out of the frame work on a none conductive surface and make sure the boards dont touch each other and do not accidentally touch and heatsinks.

[TimT]

Re: Rca L40FHD41YX9 no power

i pulled the board for this ( no room to test )

large 450 cap tested 165 -165
other caps
15.23 -15.23
12.86 -12.85
18.20 -18.20
one cap was 0 cb 5 if i remember correcty. I did replace that and retested cb5 still 0 ill have to upload better pictures. but cb5 was far right under heat sink

[ben7]

Re: Rca L40FHD41YX9 no power

The rightmost cap appears to be the filter capacitor for the SMPS controller IC (IC3). It is labelled C10. Since there is no voltage there, the controller might have gone short. Probably, some of the MOSFETS died, taking out the controller.

Check QW10 and QW9.

[TimT]

Re: Rca L40FHD41YX9 no power

yes C10 was the cap with no power. I tested QW10 and QW9 with meter set to 20 DCV and probe grounded screw on board. QW10 tested -10.69 on both joints QW9 was 0 on both joints

[ben7]

Re: Rca L40FHD41YX9 no power

yes C10 was the cap with no power. I tested QW10 and QW9 with meter set to 20 DCV and probe grounded screw on board. QW10 tested -10.69 on both joints QW9 was 0 on both joints

No, check their resistance and/or use diode check mode. Make SURE the PSU is unplugged, and the filter cap is discharged - don't want any fried DMM!

[TimT]

Re: Rca L40FHD41YX9 no power

how do i discharge the filter cap? what cap? c10 has no power

[ben7]

Re: Rca L40FHD41YX9 no power

how do i discharge the filter cap? what cap? c10 has no power

The filter cap I am referring to is the big black one. That could hold anywhere up to 400 volts, so it is a good idea to make sure it is discharged. You can check its voltage with the DMM if your not sure if its discharged or not. To discharge it, just use a 100 ohm 5 watt resistor to drain the power from it. You could also just short the terminals with a screwdriver, but that makes a LOT of sparks.

[TimT]

Re: Rca L40FHD41YX9 no power

used the screw driver QW10 8.83 QW9 7.13

[ben7]

Re: Rca L40FHD41YX9 no power

used the screw driver QW10 8.83 QW9 7.13

You measured them in ohms? Across what pins? (they are marked on the board, either G, D, or S

[TimT]

Re: Rca L40FHD41YX9 no power

did not notice they were 3 pin


QW9
- PROBE ON D
G 1455
S 1438
- PROBE ON S
G 007
D 1 =OUT OF RANGE?
-PROBE ON G
G 1
S 007

QW10

-PROBE ON S

G 1438
S 1438
-PROBE ON S
G 007
S 1
-PROBE ON G
S 008
D 1

I now have a new mulitmeter so I should take these readings again.

[budm]

Re: Rca L40FHD41YX9 no power

What scale on the meter are you using? It important to report the reading as shown the meter including and letter on the screen.
For example the reading of 007, is that 007K Ohm?, 007 M ohms?, 007 Ohms?

[TimT]

Re: Rca L40FHD41YX9 no power

im going to retest this with the new meter. its auto ranging

[TimT]

Re: Rca L40FHD41YX9 no power

new test

QW10


- PROBE ON D

S 15.65M
G 15.66M

- PROBE ON S

D 18.32M and climbing
G 08.35K

- PROBE ON G

D 21.34M and declining
S 8.35K

QW9

-PROBE ON D

S 15.34M
G 15.31M

-PROBE ON S

G 7.08K
D 23.33M and climbing

- PROBE ON G

S 7.08K
D 18.96M