JVC Model: JLC37BC3002 - Backlight not working

[dick_barton]

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.

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

I see that! Thx for linking that post. If that is the problem, where would I check next?

I searched the forum some more and found a thread with similar backlight issue but the resolution was not clear other than they used a repair kit on the power supply board from ShopJimmy.

i searched ShopJimmy and found a repair kit for a Vizio/JVC 0500-0412-1300 board (link here)
But my board is a 0500-0412-1310. (Mine is 37", that repair kit is for a 32") will they be the same kits since its just for the power supply board? (Seems all parts and boards for my model TV are out of stock everywhere) I would think that the power supply board would be similar, but the main boards would be different between different sized TVs of the similar model ranges. Not sure how that all works though. Would just hate to purchase a repair kit for a wrong board if it wont work for me.

Also, without knowing fully yet what component is bad, I am hesitant to buy anything.

[dick_barton]

Re: JVC Model: JLC37BC3002 - Backlight not working

It seems as though your backlight control voltage may be to low.
In another thread similar t your set the VBR_B voltage is much higher and they do have the backlights working. See post #4

https://www.badcaps.net/forum/showth...ighlight=VBR_B

[kyrinth021883]

Re: JVC Model: JLC37BC3002 - Backlight not working

I have checked both fuses on the board and both are good.

https://www.badcaps.net/forum/attach...6&d=1507079126
That is the is the NOSFET for the PFC Voltage booster circuit. is he 3.15A fuse close to it good?
You need to verify that you do have 3800~400V DC between the two legs of the main filter cap, the backlights inverter circuit needs that to operate.

I checked the voltage between the two legs of the main filter cap (assuming this is the largest one next to the NOSFET picture I posted?) The voltage was about 385 VDC when the TV was turned on.

[dick_barton]

Re: JVC Model: JLC37BC3002 - Backlight not working

There's a second fuse on the board. Have you checked it. Also occasionally the two transformers need to be resoldered.

[budm]

Re: JVC Model: JLC37BC3002 - Backlight not working

https://www.badcaps.net/forum/attach...6&d=1507079126
That is the is the NOSFET for the PFC Voltage booster circuit. is he 3.15A fuse close to it good?
You need to verify that you do have 3800~400V DC between the two legs of the main filter cap, the backlights inverter circuit needs that to operate.

[kyrinth021883]

Hello! I have dabbled a little with fixing a few TVs here and there as kind of a side hobby when I'm not busy. I am still totally a beginner though. I work as an avionics technician and so have a basic understanding of electronics principles.
I was recently given a JVC flatscreen from a friend at work who said the picture went out. I brought it home and did a quick check. TV does power on after plugged in, standby light good, remote functions good, TV powers on from standby good, and checked the LCD with flashlight and verified the LCD is working and seems to have a picture, but the back light does not seem to be coming on at all.
I opened up the back to check for anything obvious (bad caps, burnt marks, loose connection, etc). After not seeing anything obvious, I put a meter on it and tested each pin at the connector (the one connecting the power supply board to the main board). The following are the results (going from top to bottom of connector):

With TV in standby:

VBR_B - 0 VDC
STATUS - 0 VDC
ON/OFF - 0 VDC
ON/OFF - 0 VDC
12V - 0 VDC
12V - 0 VDC
12V - 0 VDC
GND - 0 VDC (GND ohm check good)
GND - 0 VDC (GND ohm check good)
GND - 0 VDC (GND ohm check good)
GND - 0 VDC (GND ohm check good)
5.1VSB - 5.1 VDC
5.1VSB - 5.1 VDC
5.1VSB - 5.1 VDC


With TV in ON:

VBR_B - 0.53 VDC
STATUS - 3.06 VDC
ON/OFF - 3.26 VDC
ON/OFF - 3.28 VDC
12V - 11.98 VDC
12V - 11.98 VDC
12V - 11.98 VDC
GND - 0 VDC
GND - 0 VDC
GND - 0 VDC
GND - 0 VDC
5.1VSB - 5.21 VDC
5.1VSB - 5.21 VDC
5.1VSB - 5.21 VDC

I'm not 100% sure, but I think these voltages all look correct?

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.

After not getting anywhere, I decided to inspect the boards more closely. The only thing I could find that might be a possible cause of fault is what looks like a small dead bug (ant maybe?) laying across two legs of a mosfet.
Looks like "Q602" on the power supply board (see pictures). Not experienced enough to know what 2 legs of the mosfet the dead bug are laying across. My question would be could this possibly be the cause of the fault and how could I check it? Also, what else could I check to further trouble shoot this problem. I feel like I am on the right track with it being a back lighting issue. Thank you in advance for any assistance.