JVC LT-42EM59 no picture no sound

[bayougrizz]

I have the above TV with no picture and the best I can tell no sound either. I found another thread with a similar issue, but after following those posts, I believe I have a different issue.

Could someone please help me determine the issue so I man order replacement parts?

I hope the board pictures are sufficient. If I need to more and focused on a particular area, I certainly will.

Thank you

[budm]

Re: JVC LT-42EM59 no picture no sound

Can I get closed up pictures around the connector (the one that goes to the power supply board) of the inverter board? I can see the pin names of the connector so we can see if you are getting the correct Voltages and signals or not.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

On the power supply, top right, there are a 2 connectors with cables going from the PSU to the main board. We need the pin out of those.
Here is how it works:
The PSU has a STBY voltage that is always there and that goes to the main board. When you turn on the TV, the main board returns a PSon (to turn the whole power supply on) and a BLon (back light).
So you need to measure all those pins (DC) with the TV on, the negative lead on GND or chassis ground. Post back all the voltages measured with the corresponding pin out and then we can go from there.

[budm]

Re: JVC LT-42EM59 no picture no sound

http://www.shopjimmy.com/jvc-sfn-905...upply-unit.htm

The problem is that there are no pin names for the connectors on the power supply board, the inverter board does have pin names so we can at least find out if the Voltages and the signal Voltages are OK or not.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

that's a bummer... hate that when there isn't any labeling printed on.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

Here are the pictures you requested.

Thank you for answering my post.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I measured voltage on all the pins on both connectors CapLeaker mentioned. Now, I unplugged the connectors from the power supply board and measured from each pin to ground. The only one I got voltage on was pin 5 of the CN9005 connector at 6VDC. Most of the rest measured 0VDC. On that same connector Pins 10, 9, and 7 measured .357VDC.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

CapLeaker,

here is the pin out you were looking for. I found the manual for this tv in a past thread on this forum.

[budm]

Re: JVC LT-42EM59 no picture no sound

CapLeaker,

here is the pin out you were looking for. I found the manual for this tv in a past thread on this forum.

OK, so now you do have pin names for both connectros, then report the aDCV readings with the pin names next to each Voltage readings so we can see what you have and what you do not have, do that with the TV off and then with the TV power switch activated.
For example:
CN9006: BL-ON PIN1, TV OFF = XXX V, TV ON = XXXV

Do that on both connectors.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I used to be able to plug the TV in, hit the power button and the relay(s) would click. Now I am having trouble with that. While measuring voltage for you guys, I was not able to get anything to happen when pressing the power button.

See voltage readings attached.

[budm]

Re: JVC LT-42EM59 no picture no sound

Do you have ALL the cables connected back together when you take these measurement?
STB3.5V is really 0 Volt? If it is, this one needs to be fixed.
You should check your meter's battery that it is not low.
BTW, can you give the link to the thread of that service manual of this model?
I search the thread using 'JVC LT-42EM59' and no hits.
What is the P/N as printed on the power supply board? I need to see if shopjimmy has good pictures of your power supply board.
Which one is your power supply board?
http://www.shopjimmy.com/catalogsear...=JVC+LT-42EM59

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

Hmmm... o.k pin out is a very big plus. However I have to say x2 what budm already mentioned. If STB3.5V = 0V... that's not good and that has to be fixed first. I wonder if there is a schematic for that board somewhere. That would be much nicer than tracing stuff on the board.

Anyway... food for thought... If you unplug everything from the PSU and plug the PSU in, what does STBY3.5V do?

[budm]

Re: JVC LT-42EM59 no picture no sound

It looks like he has the 9066A power supply, SJ does not have good clear pictures of the top or the bottom side of the board which I will need to be able to trace out the connections.
"Anyway... food for thought... If you unplug everything from the PSU and plug the PSU in, what does STBY3.5V do?" That is a very good question.

Picture provided by shopjimmy.

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I must have had a loose connection or something, but at any rate, I re-seated every connector carefully and remeasured with the TV plugged in and then again after pressing the power button and hearing the relay(s) click. I checked them at the power supply board and at the signal board to make sure there wasnt a connector or wire issue. The batteries in my meter are good. I keep them fresh as I use this meter for work everyday..but thanks for bringing that up, I have made that mistake in the past!

There is no wire on Pin 6 (STB3.5V), but I measured the pin through the plugged in connector and still got 0VDC.

The power supply part number on the board is SFN-9066A.

I unplugged all connectors from the power supply board, and just plugged that board in. Nothing changed, I still have 0VDC on STB3.5.

[budm]

Re: JVC LT-42EM59 no picture no sound

"There is no wire on Pin 6 (STB3.5V)" That means the main board does not use this Voltage to run, it uses only the 5VSTBY.

[budm]

Re: JVC LT-42EM59 no picture no sound

" I re-seated every connector carefully and remeasured with the TV plugged in and then again after pressing the power button and hearing the relay(s) click"

There must be an error in your measurement, to have the relays click on you MUST have DCV at CN9006 pin 6 (MAIN_POW), and at PIN 8 (PFC_POW) because those two transistors Q9001 and Q9002 which drive the relays must be getting the command on signals from the main board to turn them on.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

I must have had a loose connection or something, but at any rate, I re-seated every connector carefully and remeasured with the TV plugged in and then again after pressing the power button and hearing the relay(s) click. I checked them at the power supply board and at the signal board to make sure there wasnt a connector or wire issue. The batteries in my meter are good. I keep them fresh as I use this meter for work everyday..but thanks for bringing that up, I have made that mistake in the past!

There is no wire on Pin 6 (STB3.5V), but I measured the pin through the plugged in connector and still got 0VDC.

The power supply part number on the board is SFN-9066A.

I unplugged all connectors from the power supply board, and just plugged that board in. Nothing changed, I still have 0VDC on STB3.5.

O.k. on the 3.5VSTBY and since the pin is missing, there wont be any voltage there.

If you pressed that power button and then the relays clicked that means something has changed on the pins between the main board and the PSU. Did you check both connectors and not just one? I am sure that the main board returned at least the PSon (Main POW) signal. Nice schematics budm!

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

I got 3.1VDC on both pin 6 and 8 on CN9006 this time. When I press the power button the relays click and about 10 seconds later they click again (apparently off I reckon). I didn't realize this the first time. I had to be quicker to catch the voltage reading.

[CapLeaker]

Re: JVC LT-42EM59 no picture no sound

what about pin 1 and 9?

[bayougrizz]

Re: JVC LT-42EM59 no picture no sound

No wires in Pin 4,5,7,9, or 10. Pin 1 measured .740VDC with the power on. Pin 4 measured .5VDC and Pin 5 had no voltage.