jvc lt-50c550 power supply problem

[chrislyons]

hello i hope i can get help here on this tv, no back lights , all leds bulbs checked working had screen out , the power supply seems to be at fault. when powerd up all correct voltages are there, apart from led, con,1 con2, no power i marked that in red, common fault with tv set but cant find any repair tips ;-( power supply in question tv5001-zc02

[budm]

Re: jvc lt-50c550 power supply problem

Put all connectors back in place.
1) What DC Voltage do you have on the two legs of the 3 mail filter caps in the HOT side when you turn on the TV and measured right between the two legs of the caps? 380 ~ 400vdc?
2) "when powered up all correct voltages are there" Are you saying the control Voltages are also correct, I.E. PS-ON, BL-ON, DIM...? What are the DC Voltage on each pin of the connector that goes to the main board? The pins look to be labeled so put down the pin name and follow by the Voltage reading for each pin so we can easily see what it has and does not have when TV is off and when power switch is activated.
3) Please provide pictures of the whole backside of the TV showing all the boards.

[chrislyons]

Re: jvc lt-50c550 power supply problem

i may have found the problem this yellow transformer has feed 326v but reading zero voltage coming out

[dick_barton]

Re: jvc lt-50c550 power supply problem

If the circuit that drives the transformer primary with an oscillating voltage is not working then there will be no output.

What were the results of the checks suggested in post #2

[dick_barton]

Re: jvc lt-50c550 power supply problem

If the circuit that drives the transformer primary with an oscillating voltage is not working then there will be no output.

Looking at circuit diagram this is a transformer in series with the PFC supply and whose secondary provides the zero crossing for U102 so I would say there's nothing wrong with this transformer.

[nomoresonys]

Re: jvc lt-50c550 power supply problem

Can you do the test?? it's hard to remotely help without the info, you need to help us help you.

[R_J]

Re: jvc lt-50c550 power supply problem

You need to check the voltage across EC101,2 or3 with the tv in standby (OFF) and then AGAIN with the tv turned ON. This will give an indication of the PFC circuit operation.
In the first post you said "when powerd up all correct voltages are there, apart from led" So the power supply is likely working.
Report these voltages.

Next check the voltage on the + of EC202,3 or 4 as the tv is being turned ON. don't wait untill the tv is already ON to check this voltage.

[budm]

Re: jvc lt-50c550 power supply problem

i may have found the problem this yellow transformer has feed 326v but reading zero voltage coming out

That is PFC Inuductor. You do know what PFC is used for in TV, right?
You need to follow instructions and requests if you want to get help.
1) We need to know if the PFC boosted Voltage is working or not.
2) We need to know if all the control Voltages are present or not.

[SmartPiter]

Re: jvc lt-50c550 power supply problem

It is good to hear you guys on the level of expertise you present.

All about powering JVC lt-50c550.

I am trying to diagnose the problem which is quite common in search results, but there is no clear solution for it: JVC lt-50c550

The issue is like this:
I Plug TV in to power, red standby light illuminates, hit the power button, screen illuminates for half a second with the JVC logo then goes off, TV won't then do anything unless you disconnect and reconnect the power which then you get the red standby light again.

The TV was working fine and one night turned off and never turned on properly since.


I was trying to get to LED stripes, but it seems also there is no bolt system of mounting and wondering about the method of opening the bezel to do it...

[neilc6]

Re: jvc lt-50c550 power supply problem

Flash of backlights/logo is a symptom of bad backlights. It is detected and then the driver circuit shuts it down. Depending on model, it the error signal is passed back to the main board then the main board could shut down the TV is as well.

[SmartPiter]

Re: jvc lt-50c550 power supply problem

Flash of backlights/logo is a symptom of bad backlights. It is detected and then the driver circuit shuts it down. Depending on model, it has the error signal is passed back to the main board then the main board could shut down the TV is as well.

Thanks for prompt answer, the curious is that TV is in need to be disconnected from mains to be turned off or tested again, BTW did find the video for similar TV (~40") about opening: some hard words about all front bezel glued... tested and now can open it.

https://www.youtube.com/watch?v=5lTa2oXxyRI

New Led strips and adhesive conductive tape ordered. Will post results of repair in November...