Rca l37wd12 lcd tv

[gelatinous]

Re: Rca l37wd12 lcd tv

I don't know if it's related but I had a similar problem with a Toshiba (no standby light, falling at the first hurdle) - turned out to be the 2.5V supply on the scaler for the DDR had dropped out. Very strange. Don't know if it is related.Have you posted a picture of your scaler board?

I know that there's one 2.5V supply on the board and it is active when the system is in standby. It is also the voltage used to run the keyboard buttons..

I will post the pictures of the scaler board shortly, they are still on my phone.

[tom66]

Re: Rca l37wd12 lcd tv

I don't know if it's related but I had a similar problem with a Toshiba (no standby light, falling at the first hurdle) - turned out to be the 2.5V supply on the scaler for the DDR had dropped out. Very strange. Don't know if it is related.Have you posted a picture of your scaler board?

[gelatinous]

Re: Rca l37wd12 lcd tv

thanks budm!

With these diagrams I have determined that pin 2 on the keyboard is just high enough to enable TK002, which in turn disables TK001 which in turn turns off the standby LED. So once again this is pointing to a main board issue as pin 2 connects to the main board.

I will hopefully be able to trace this line soon, though I have a feeling that it is going to run to the same processor as the TV_KEY and the P-ON signals.

[budm]

Re: Rca l37wd12 lcd tv

Diagrams for keyboard

[budm]

Re: Rca l37wd12 lcd tv

I will try to locate the manual when I get home.

[gelatinous]

Re: Rca l37wd12 lcd tv

Thanks budm, I've registered and am waiting to be able to login. When you get a chance would you be able to check the button board schematic and see what the two SOT23 parts are?

[budm]

Re: Rca l37wd12 lcd tv

I ordered from RCA in 2007, $50.

http://www.thomsonnetwork.com/EN/Public

[gelatinous]

Re: Rca l37wd12 lcd tv

Thanks budm, the layout of your tv looks identical to mine. can I ask where you found the service manual? I've been looking but haven't had much luck.

[budm]

Re: Rca l37wd12 lcd tv

My 26" is used in my kitchen every day. I have the service manual also, so I look at the board diagram and see what is like.
My TV's buttons are ont he right side of the screen.
http://s807.photobucket.com/albums/y...t=DSCF1331.jpg

[gelatinous]

Re: Rca l37wd12 lcd tv

I think I may have found a problem on the button board. I can't tell if this part is a transistor or a double diode... If my memory is correct the part is labelled TK002 and is SOT23 packaging

Pins:
1
23

Diode check:
2-3 ........1807....... OL
1-2 .........OL.......OL
1-3 .........OL.......OL

in board and out of board. So far as I can tell this part has to do with the standby LED, it may have more function but I haven't looked at the circuit that close. I wish I'd brought the board with me to work so I could tinker with it a little.

Pin 1 is connected to the 5V standby through a 2k resistor *I think*, I don't have the circuit with me now to verify.

Budm is your 26 in use? I don't know if the button board is the same or not but I would at least like to try and replace this part before looking for a main board... I had a look on ebay and none were showing up for me.

[budm]

Re: Rca l37wd12 lcd tv

Since the main board does not generate the PS_ON signal, so more likely it is not generating the BL_ON signal either, main board will more likely to be the problem.

[gelatinous]

Re: Rca l37wd12 lcd tv

Ok, I jumpered the 5V standby to the P-ON and the relay clicked and voltages came up. 12V was 11.7V 24V was 23.9V. Power LED turned green. No Backlights were present... Inverter voltage was ~2V.

The main processor that the button signals go to had 1.8V and 3.3V when in standby but no standby LED was present.

I am inclined to say that this is a main board issue and that it is going to take a while to troubleshoot.

[gelatinous]

Re: Rca l37wd12 lcd tv

But you said the TV does not power on anyway with the relay forced on?

Some TVs do a self-test when first plugged in. They will power up the PSU, check outputs are good, then power down. If not, they go into a lock out mode. Don't ask me why... Both Toshiba 32WLT66S and 42WLT66 are confirmed to do this, as are all 17PWxx based Vestel and some Samsung TVs. Not sure who makes the RCA chassis, probably not RCA themselves!

yes the unit does not power on at all. However, I think that this is because the PSU is not seeing the 5V P-ON signal from the main board, telling it to turn on. The main board is not generating this signal at all.

When I first got this TV plugging it in a leaving it for a while, then quickly unplugging and replugging it in would turn it on, but all buttons would be unresponsive.

Since working on the 1W board the unit now does nothing. The 5V standby is still getting to the main board and I can measure ~160V at the rectifier output on the PSU but the main outputs do nothing and it is totally silent.

I never checked to see if the supply was coming up before because I never heard the relay click unless the TV was turning on.

Without the main board telling the 1W board the engage the relay the PSU gets no power.

Sorry if my response seems jumbled, I'm at work and have had far too much coffee.

Also I will check the boards for a manufacturer identification.

[tom66]

Re: Rca l37wd12 lcd tv

I had no sound from the PSU at all when it was connected. Before I replaced the cap on teh 1W board I was able to hear a high pitched squeal from the 1W board, but the PSU itself has always been silent.

I noticed that the 5V signal to engage the relay on the 1W board is connected to the P-ON signal to the PSU via a zero ohm resistor on the main board. I have also traced the signal to a pin on one of the micro processors, there appears to only be a 100ohm resistor between the microprocessor and the 5V enable. I hope to be able to trace the button press line on the main board next and see if something preventing the signal from getting to the processor or if the processor is dead / not being powered.

I'm pretty sure that the issue is on the mainboard, but I don't have a 5V supply to imitate the P-ON signal for the PSU so I can't eliminate it yet..

But you said the TV does not power on anyway with the relay forced on?

Some TVs do a self-test when first plugged in. They will power up the PSU, check outputs are good, then power down. If not, they go into a lock out mode. Don't ask me why... Both Toshiba 32WLT66S and 42WLT66 are confirmed to do this, as are all 17PWxx based Vestel and some Samsung TVs. Not sure who makes the RCA chassis, probably not RCA themselves!

[gelatinous]

Re: Rca l37wd12 lcd tv

Check the diodes on the output for shorts.

Do you notice a ticking or clicking sound at a regular interval from the PSU?

I had no sound from the PSU at all when it was connected. Before I replaced the cap on teh 1W board I was able to hear a high pitched squeal from the 1W board, but the PSU itself has always been silent.

I noticed that the 5V signal to engage the relay on the 1W board is connected to the P-ON signal to the PSU via a zero ohm resistor on the main board. I have also traced the signal to a pin on one of the micro processors, there appears to only be a 100ohm resistor between the microprocessor and the 5V enable. I hope to be able to trace the button press line on the main board next and see if something preventing the signal from getting to the processor or if the processor is dead / not being powered.

I'm pretty sure that the issue is on the mainboard, but I don't have a 5V supply to imitate the P-ON signal for the PSU so I can't eliminate it yet..

[tom66]

Re: Rca l37wd12 lcd tv

Check the diodes on the output for shorts.

Do you notice a ticking or clicking sound at a regular interval from the PSU?

[gelatinous]

Re: Rca l37wd12 lcd tv

Is there a fuse on the input to the PSU? Is it good?

What voltage do you measure across the startup cap?

What manufacturer output caps are used? (They look like Nichicon which are very good.)

I've replaced all the output caps as they were bulging, the TV did exibit the same symptoms after though, it's only been since I worked on the 1W board that it stopped turning on at all... I still get 5V standby to the mainboard, but even bypassing the relay on the 1W board gives me zero output on the PSU now. The inline fuse on both the 1W board and the PSU are good.

I will have to snag some wire from work so I can measure across the startup cap.

[selldoor]

Re: Rca l37wd12 lcd tv

I am also having the same exact issue with the same exact TV.
All the caps on my 1W board tested fine and I see no bulged or leaking caps anywere.
My TV would also work if left on but then one day the buttons stopped responding so i unplugged it and plugged it back in, it would turn on each time but wouldn't always respond to buttons on tv or remote. My boss gave this TV to me and It was working when I took it from the office. After a 15 min drive it has yet to turn back on. When I plug it in, I hear a little electrical charge but no CLICK like it used to. Solid red light on front.

Do you need any help troubleshooting your set?
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.

[tom66]

Re: Rca l37wd12 lcd tv

Is there a fuse on the input to the PSU? Is it good?

What voltage do you measure across the startup cap?

What manufacturer output caps are used? (They look like Nichicon which are very good.)

[gelatinous]

Re: Rca l37wd12 lcd tv

Here are some shots of the PSU, I noticed that there is a section on the bottom that looks to have gotten hot, looks to be one of the transformer windings.

I tried changing the startup cap 10uF 50V on the PWM PFC chip but that had no effect.

It's hard for me to measure the voltages on this supply as it has to be in the TV for me to power it up... I don't have a good selection of testing cables at my house. I was able to measure ~160VDC at the output of the bridge though.

EDIT: I just noticed that my attachments are messed up.
EDIT 2: I also just noticed that in one of the pictures of the bottom of the board there is mention of the P-ON signal I was talking about. I will work on getting some decent pictures of the mainboard soon.