JVC Model: JLC37BC3002 - Backlight not working

[nsilvang]

Re: JVC Model: JLC37BC3002 - Backlight not working

i need the bios dump for this tv jlc37bc3002

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Did not notice that in the first post.
It may be a bad cfl lamp arching.

No, it is definitely blue LED lights. the one under the PS/Inverter board I can actually see the when I look under it. The light in the top corner is the same light and they both light and fade out the same together. Plus if there were arcing and such, i think I would hear it and it would look a lot different lol.

[Dumah Brazorf]

Re: JVC Model: JLC37BC3002 - Backlight not working

When first turned on, i think I see some faint blue-ish light from the top left corner (looking at the back) through some of the holes in the metal backplate. But this only lasts a second or two. Can't tell if this is the backlighting trying to fire off, or something else.

Did not notice that in the first post.
It may be a bad cfl lamp arching.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Its was STATUS - 3.31, same as before (also get all 3 12VDCs)

[dick_barton]

Re: JVC Model: JLC37BC3002 - Backlight not working

It certainly looks as Budm says. Out of curiosity what was the Status voltage when you had jumped all three points? From the link in an earlier post given on this thread, when the set was displaying the logo
VBR_B - 3.22V
Status - 0.0V

I suspect that the Status voltage (3.06V) is at fault condition and as a result disabling VBR_B

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Ok, that's what I was wanting to hear from the experts I will search for a new board. Thanks a bunch for the great help! Will update once I get a new one.

[budm]

Re: JVC Model: JLC37BC3002 - Backlight not working

At since point since you did test the power supply/inverter board by itself using force on with resistors but still no backlights then you do have power supply board problem.
VBR missing is the main board problem.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Ok, I was able to test using 3 resistors. Using a 1K resistor for each one, I jumpered 5.1V to INV_ON, 5.1 to REMOTE_ON, and 5.1 to VBR_B. I get the same as before. Once power is applied, all I get is the blue LED lights come on a few seconds then fade out. No backlight. I read the voltages, all the same as listed the most recent time above, onl difference is the VBR_B voltage being about 0.68V.

Since you mentioned it should be above 1V, I used a lower ohm resistor (470 ohm) and tried again. This time VBR_B voltage was 1.2V. Same result. No backlight. Blue LEDs behaving the same. Starting to think its just a back PS/Inverter board. Curious to try to find what component(s) are bad on it though.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Ok, I will try using 3 once I get home

[budm]

Re: JVC Model: JLC37BC3002 - Backlight not working

OK, I think I understand what you describe now after reading this statement again "Same thing happens as when I push the power button in normal configuration. "
So it looks like you need a third resistor (1K) between VBR_B and the 5.1STB also to get the backlights to come on for this power board testing.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

I'm sorry, I'm not following. I disconnected the power supply board connector from the main board for that test. I do not see any other connections to disconnect.

[budm]

Re: JVC Model: JLC37BC3002 - Backlight not working

When using force on, you must remove the signal control wires that go back to the main board first.
VBR_B (dimmin control) - 0 VDC = no backlights, it has to have 1V or more typ.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Ok, repeated same test, this time with both the 5.1VSB + INV_ON and 5.1VSB + REMOTE_ON jumpered with 1K ohm resistors respectively.

Same thing happens as when I push the power button in normal configuration. The aforementioned blue LED lights turn on for a few seconds then fade out. Still no backlight. This time i did get the 12v.
Read the voltages on the connector:

VBR_B - 0 VDC
STATUS - 3.31 VDC
INV_ON - 5.01 VDC
REMOTE_ON - 5.22 VDC
12V - 11.84 VDC
12V - 11.84 VDC
12V - 11.84 VDC
GND - 0
GND - 0
GND - 0
GND - 0
5.1STB - 5.1 VDC
5.1STB - 5.1 VDC
5.1STB - 5.1 VDC

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Can you post a picture of the underside of the board showing what the connector pin names are.

Hi, sorry it took so long to post a pic. Couldn't take one until I got home from work. Here is the pic you requested.

[dick_barton]

Re: JVC Model: JLC37BC3002 - Backlight not working

Having the correct pinouts as seen from underneath the board it looks like you have to jumper 5.1VSTB to Remote ON/OFF and 5.1VSTB to Inv ON/OFF using the resistors and then check that your backlights come on and stay on.
Explains why your 12V did not come on in the previous test.

Photo's courtesy of Shopjimmy

[dick_barton]

Re: JVC Model: JLC37BC3002 - Backlight not working

Can you post a picture of the underside of the board showing what the connector pin names are.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

I don't think you have a power supply board problem.
If you disconnect you power supply from the mainboard and on the power supply, attach a 1K resistor between 5.1VSTB and ON/OFF and a second 1K resistor between 5.1VSTB and VBR_B and check that your backlights come on and stay on.

Ok, got some 1K ohm resistors. I did the test you mentioned. Disconnected the main board from the power supply. Put 1K resistor between one of the 5.1VSTB and ON/OFF (INV ON/OFF, had to look at back of board to know which on/off it was) and also put one between a 5.1VSTB and VBR_B.

The results: Plugged the TV in..... and nothing. No backlight. Getting good 5.1VSTB's. 4.95VDC on the INV_ON/OFF pin (power supply side of resistor). I get 0.6VDC on VBR_B pin (power supply board side of resistor). And no 12VDC's at all. (Guessing that is normal since connector is disconnected?)
Is the backlight supposed to turn on and stay on with just this set up using the resistors? Still trying to figure out if the power supply/Inverter board or the main board is bad.

Reconnected main board connector. Decided to take voltage readings again and watch while toggle the ON/OFF button. All voltages are as stated above in previous post, with the one new thing I noticed. When TV is in standby (just plugged in and red LED light on front) VBR_B voltage reads 0VDC. When I turn the TV on (w/ power button) VBR_B goes to 1.2VDC. After about 3-5 seconds, what I thought looked like the backlight in the top left corner (through some holes), turns off, (I turned the lights down to see it better) and the VBR_B voltage drops to 0.4VDC. The VBR_B voltage stays at 0.4VDC until I cycle the power switch again. Then I get the same result each time. Turns out that the blue light is actually a blue LED on the bottom side of the power supply/inverter board and apparently a blue LED in the top right corner under the metal someplace. Just LEDs not the backlights lol.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

Post a pic of the back of the power board.

I have taken some, please let me know if you want me to try to get better quality or closer up. I can try.

[Dumah Brazorf]

Re: JVC Model: JLC37BC3002 - Backlight not working

Post a pic of the back of the power board.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

I don't think you have a power supply board problem.
If you disconnect you power supply from the mainboard and on the power supply, attach a 1K resistor between 5.1VSTB and ON/OFF and a second 1K resistor between 5.1VSTB and VBR_B and check that your backlights come on and stay on.

Ok, I will try that. I have to get some resistors first though. Don't have any laying around at the moment. Thx. Will post my findings afterward.