RCA LED42C45RQ screen blinks, but will not stay on

[Pioneerx01]

I am trying to fix up LED42C45RQ, but it has been problematic. When I got it, I plugged it in. Red power LED lit up, TV did nothing (as it should, I believe). When I press the power button on the TV (I have no remote) the red LED turns off, and 3 second later the TV screen flashed twice fast (at least LED's do) and nothing shows on the screen while it does. Red LED remains off, and you can't do anything with the TV no matter what you press. I have to re-plug it to AC and then I can repeat the process.

I have opened the TV up, nothing looked wrong. When the TV is in stand-by (red LED on) I get 5V on +5Vsb, but rest are at 0V. When I power the TV on, I get proper voltages all over, but after the screen flashes (3 seconds after power up) the +5 and +12V drop to 0V, and all I get is 5V on +5Vsb and ON/OFF. After the TV's power up, and after the flashes, I am reading 3V on the BL-ON pin.

I have tried disconnecting the LED's from the PSU board, and hook up multi-meter instead, but no change. LED voltage comes on to over 120VDC (maybe more, I have no max function on multi-meter) and then it slowly drops down to 0V. rest of the voltages are as described above. Then I disconnected the T-Con, but same issue. I have disconnected the IR, same issue. I have quickly disconnected the buttons after I power it on, but same issue.

I have purchased replacement PSU, installed it, but same thing happened. So I have got replacement Main, but same thing. Only thing I did not replace was the T-Con, but that does not sound like a T-Con issue, especially if it was disconnected from the main. Both parts were used, but from reputable vendors. The odds of me getting a defective component that has the same issue as my original one are relatively high, but not impossible. I am at a loss as to what to do next.

Thoughts?
Thanks

PSU - RS100S-3T01, RE46HQ1053
Main - 42RE01M3393LNA5-B1, MK-RE01-131209-ZQ201
T-Con - 42T24-C08, T420HVD011.0, TT-5542T24C10-361-M058745-05427-03

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on (Not back-light issue)

Anyone?

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

I wonder if maybe you have a bad LED. It sounds like something is putting it in protect mode, and you've pretty much ruled everything else out.

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

I wonder if maybe you have a bad LED. It sounds like something is putting it in protect mode, and you've pretty much ruled everything else out.

I have disconnected the LED's from the TV and put volt meter on in instead, to eliminate them from the equation. See third paragraph.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

I have disconnected the LED's from the TV and put volt meter on in instead, to eliminate them from the equation. See third paragraph.

That's not really eliminating them from the equation though. You are taking a voltage measurement, but you don't know what the correct voltage should be. Also, without the LEDs connected, it is going to shut down immediately.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

It's actually a bad idea to assume you've ruled anything out unless you are 100% certain it came from a working TV. When it's switched on, but after it's gone into protect, do you still have around 3 volts on the on/off pin? You're going to need a better meter too. Something capable of over 400vdc so you can check the PFC circuit.

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

Sorry for the long delay, last few days were problematic.

You are correct, there is a chance that LED's are bad. I just took the lazy way out with diagnosis. I did take time to take out the panel and look at the LED's and they are all fine. For that brief half a second they are on. See picture.

Yes, I still get 3V on the panel on/off pin, even after the LED's are done flashing.

As to the volt meter it does go up to 1000VDC, it just does not have min/max option, so when the LED's flash on for less than a second, the volt meter is not fast enough to catch the peak before the voltage starts to drop down again.

The interesting thing is that once the TV flashes on, I still get 3V on on/off pin, but I am not able to turn the TV off, so I get 0V on that pin. I can press the power button all I want I will not get anything from the TV. I have to physically unplug in and plug it back in to repeat the process. Makes me think is main board related somehow.

Thoughts?
Thanks

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

If you have a 5k resistor you can disconnect the main board and jumper the 5v standby to the on/off pin and also to bl_on. That should switch on the power supply and turn on the backlights.

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

OK, I did that. The LEDs came on continuous full power, but only for about 5 seconds or so. After that darkness. I have to re-plug to get the same result.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

I kind of thought you'd get that result. Try to get a voltage reading across the PFC cap. That's going to be the big capacitor, and you will put one probe on each pin. You should see 160 to 170 volts when it's off, and 370 to 400 when it's on.

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

OK, new "problem." After I have written the last response, I have put the TV's panel and filter back together. Now when I jump the pins (same way as I did before) the LED's flash once for less than a second and then turn off. It is not the same flash as I was originally getting which was two very fast ones, this one is slower and one flash only.

As to the capacitor, it reads 162.5V when off, but does not seem to increase at all when LED's are on for that brief moment. I did this several times, it was always in 162.5V area.

When I remove the resistors and plug the main board in, I am back to same flashes as I did originally. Capacitor is still at 162.5V in this set-up as well.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

Sounds like the PFC isn't switching on. Can you get some good clear pics of the bottom of the board?

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

Pictures I can do. I have marked the capacitor contacts in the picture for reference. Red = hot

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

ZD103 looks burned. Can you test it?

It's the glass diode at the top (bottom of board) near the Cold/Hot line.

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

It just looks burned. It was soldered on with the print showing, its just the black letters. It reads OK.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

What are the part numbers on the 2 ICs on the hot side?

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

Both read: I D7750RGR 1332AG

[Pioneerx01]

Re: RCA LED42C45RQ screen blinks, but will not stay on

That is an LD7750RGR (L not I). They are hard to read.

[lookimback]

Re: RCA LED42C45RQ screen blinks, but will not stay on

Here's the datasheet for them. They're PWM controllers. They have a protect function which latches until the power is cycled. That sounds familiar. I'm calling it a night. Tomorrow I'll help you troubleshoot the circuit.

[budm]

Re: RCA LED42C45RQ screen blinks, but will not stay on

There is no PFC Voltage booster in this power supply board.