Rca 42la45rq

[toddw65]

Hi all.

Someone gave me this tv so I'm trying to get it up and running again. The set powers up and the backlights come on and stay on for a while, but no picture, sound, menu, etc. I've hooked up an HDMI source and tried blindly switching inputs but I can't really tell if I've stumbled across the right input or not.

Thoughts on where to start?

Thanks,
Todd

[toddw65]

Re: Rca 42la45rq

Don't see a way to edit my post, but I wanted to add that the remote will not power the tv off/on which I would suspect means something other than just a display failure.

[budm]

Re: Rca 42la45rq

So the backlights stay on but the screen just has slight glow?
We need the pictures that show all the boards and how all the boards are connected together. The power switch on the TV works, right?
We need to see if the T-CON is getting the 5V/12V from the main board or not.
History of this TV on how it went out? Surge/ Lighting?
You may have EEPROM problem:
http://www.shopjimmy.com/catalogsear...q=Rca+42la45rq

[toddw65]

Re: Rca 42la45rq

So the backlights stay on but the screen just has slight glow?
We need the pictures that show all the boards and how all the boards are connected together. The power switch on the TV works, right?
We need to see if the T-CON is getting the 5V/12V from the main board or not.
History of this TV on how it went out? Surge/ Lighting?
You may have EEPROM problem:
http://www.shopjimmy.com/catalogsear...q=Rca+42la45rq

Backlights do stay on fully and the screen glows a dim gray. Power button works. I don't have any solid info on how it went out. Only that "a board was replaced under warranty" a year ago and then it "went out again" and the lady did mention that they only use the remote with their new TV because of static in the winter.

Not sure where to measure voltage for the T-CON, but assuming the smallest board is the T-CON, I measured from chassis to either side of F1 and get nothing. Does that help?

[budm]

Re: Rca 42la45rq

Backlights do stay on fully and the screen glows a dim gray. Power button works. I don't have any solid info on how it went out. Only that "a board was replaced under warranty" a year ago and then it "went out again" and the lady did mention that they only use the remote with their new TV because of static in the winter.

Not sure where to measure voltage for the T-CON, but assuming the smallest board is the T-CON, I measured from chassis to either side of F1 and get nothing. Does that help?

OK, so the main board is not sending the Voltage to run the T-CON. There should be a switched MOSFET that is controlled by the main board processor to turn on that MOSFET (it is being used as an ON/OFF switch).
So the bottom line is you have to trace out the main board to locate that MOSFET.

[toddw65]

Re: Rca 42la45rq

OK, so the main board is not sending the Voltage to run the T-CON. There should be a switched MOSFET that is controlled by the main board processor to turn on that MOSFET (it is being used as an ON/OFF switch).
So the bottom line is you have to trace out the main board to locate that MOSFET.

Ok. That makes sense. Out of curiosity, what's the jumper for on the main board that switches between 5v & 12v?

[budm]

Re: Rca 42la45rq

Ok. That makes sense. Out of curiosity, what's the jumper for on the main board that switches between 5v & 12v?

OK, sorry for confusing you about the DCV for T-CON board, some of T-CONs use 5VDC, some may use 12VDC to run, so you need to look up the spec sheet of the LCD panel to find what the Voltage should be 5V or 12V for the T-CON.

[toddw65]

Re: Rca 42la45rq

Ok. No problem. It's jumpered to 12V but either way I'll find the MOSFET and look it up. Thanks.

[toddw65]

Re: Rca 42la45rq

Ok. I looked up the panel and it is 12V. However, I've gone all over the Main board and can't find anything I can identify as a MOSFET. Lots of various 1117 regulators, flash mem, transistors, etc., but nothing I can identify as a MOSFET. I've attached some pics of what I was able to identify.

[toddw65]

Re: Rca 42la45rq

I decided to go back and do some voltage checks on the pb which I guess I should have started with in the 1st place. Not sure what it means, but what I found was interesting. I've attached some larger pics of the pb and one of the connector where I measured the voltages...with everything plugged in of course.

The +5VSB is at 5v as expected in standby and PS_ON goes high when I hit the power button. Looking at the right side of the connector, the top 12V position, (the second 12V isn't used), and both 5V positions have the expected/listed voltages on each when in standby. They stay at those voltages when you hit the power button. Then, as soon as the backlights come on, the 12v drops to about 4.5V & both 5v positions on the right of the connector go to about 0.6V. Turn the power off with the switch and the voltages come back. No idea what it means, but it doesn't seem normal to me.

[budm]

Re: Rca 42la45rq

I decided to go back and do some voltage checks on the pb which I guess I should have started with in the 1st place. Not sure what it means, but what I found was interesting. I've attached some larger pics of the pb and one of the connector where I measured the voltages...with everything plugged in of course.

The +5VSB is at 5v as expected in standby and PS_ON goes high when I hit the power button. Looking at the right side of the connector, the top 12V position, (the second 12V isn't used), and both 5V positions have the expected/listed voltages on each when in standby. They stay at those voltages when you hit the power button. Then, as soon as the backlights come on, the 12v drops to about 4.5V & both 5v positions on the right of the connector go to about 0.6V. Turn the power off with the switch and the voltages come back. No idea what it means, but it doesn't seem normal to me.

But with this condition that the switched 12V and switched 5V have drops out, the backlights still stay on, right?
Did connect the cable (LVDS cable) between the main board and the T-CON board to see if the switched 12V and switched 5V will stay on.

[toddw65]

Re: Rca 42la45rq

Right. The backlights stay on and if I disconnect the LVDS cable, its the same result.

[budm]

Re: Rca 42la45rq

'Right. The backlights stay on and if I disconnect the LVDS cable, its the same result.' and the 12V still drops out, right?

So that may explain why you do not have Voltage at the T-CON since the 12V drops out.
So we need to find out why the switched 5V, 12V drop out. I will have to trace the power supply board.

[toddw65]

Re: Rca 42la45rq

Ok. I don't know if it was coincidence or not, but in messing with this some more I burned my finger on EC405, a 1000uf, 25 cap that's just to right of CON5 on the power board so I replaced it. Now, when I turn the power on, the backlights come on just like before but both the 5v & 12v lines hold. Now power is getting to the main board, but it's still not getting to the TCON board.

[budm]

Re: Rca 42la45rq

Sounds like the cap was installed backward.
Need to find that switched MOSFET that supplies the 12V to the T-CON next.

[toddw65]

Re: Rca 42la45rq

Any idea what these are? I've googled with no luck. Thanks.

[toddw65]

Re: Rca 42la45rq

Ok. I *think* the H1A is an NPN transistor. Correct? Still No idea on the WPW7. If someone knows what it is or how to decode it that would be great.

In trying to figure out where I'm losing the 12v that should be going to the TCON, I've traced the 12v to these two ICs, but I'm not sure where to go next.

[budm]

Re: Rca 42la45rq

WP7W is most likely to be the P-CH MOSFET, you can see that the 12V is fed to the Source (right pin) but nothing is at the Drain (top pin) because the GATE (left pin) is at 11.61V, it need to be at least 2~3V < than the Source pin Voltage.
To have the Gate Voltage goes lower the H1A NPN needs to be bias ON so the Collector (top pin) will go low, right now you are getting 0V between Base (left pin) and the Emitter (right pin) that means the controller is not sending the signal to turn on the H1A.
You can force on the MOSFET by using 2~3K resistor between GATE and GND.

[toddw65]

Re: Rca 42la45rq

WP7W is most likely to be the P-CH MOSFET, you can see that the 12V is fed to the Source (right pin) but nothing is at the Drain (top pin) because the GATE (left pin) is at 11.61V, it need to be at least 2~3V < than the Source pin Voltage.
To have the Gate Voltage goes lower the H1A NPN needs to be bias ON so the Collector (top pin) will go low, right now you are getting 0V between Base (left pin) and the Emitter (right pin) that means the controller is not sending the signal to turn on the H1A.
You can force on the MOSFET by using 2~3K resistor between GATE and GND.

Great info! Thanks. Is there a way to decode these ICs in order to find proper replacements when needed?

[budm]

Re: Rca 42la45rq

At this point I do not think they are bad, you are not getting the 12V at the Drain pin because the Transistor is not getting the command on to bias on that NPN transistor, unless it has shorted out Emitter to Base junction.