RCA 46LA45RQ no backlight

[Jim1590]

Greetings all again. Craigslist freebie here. No back light after a minute or two when powered on. Flashlight test shows that the image is still on the screen.

Opened it up and got 23-24 volts on all 5 pins going from power board to the backlight inverter board. When the backlight cut out, no change in the readings.

Right now I am thinking a bad cap somewhere on the backlight board. There are 8 caps at 35v 390uf. Since the TV is 7 years old, I might as well replace all 8.

Now I have a bag of 35v 470uf caps from a prev repair. Was just as cheap to buy the 50 count bag as the 4 I needed. Brand is Chenxing off of Amazon.

Can I use the caps on hand? Or should I just buy the 390uf ones?

Next post with have pics of the boards.

Thanks

[Jim1590]

Re: RCA 46LA45RQ no backlight

First set

[Jim1590]

Re: RCA 46LA45RQ no backlight

Second set

[Jim1590]

Re: RCA 46LA45RQ no backlight

Anyone?

[finntricky]

Re: RCA 46LA45RQ no backlight

take the inverter out and check the back for burn marks/discolouring, that will give an idea as to where there may be a problem,

[Jim1590]

Re: RCA 46LA45RQ no backlight

Nothing on the back. Looks like there is no tracings or components at all. On the front, most of the solder points have at least some Browning.

[Andrew F. Ali]

Re: RCA 46LA45RQ no backlight

Check those 2 fuses on the Inv Bd. Ckeck if there is voltage on both sides of each fuse.

[Jim1590]

Re: RCA 46LA45RQ no backlight

Not at home to test right now, but wouldn't a bad fuse be bad all the time? The backlight works for a few min and incidently it works much longer if I have the back cover off. Discovered that when I was testing. That's why I thought heat related cap issues.

[DOPPLERBOB]

Re: RCA 46LA45RQ no backlight

Try using a heat gun and freeze spray to see if you can narrow down the heat related problem area. (providing you have a heat gun and freeze spray of course). You can substitute the heat gun with a hair dryer but it doesn't direct the heat into a small area as good. But it does heat up areas quicker and you then can use the freeze spray to isolate the problem.

[CapLeaker]

Re: RCA 46LA45RQ no backlight

Since the back lights come on for the first minute or two and then go out, I rule out capacitors. My bet is on a bad transformer or a bad bulb, some component that draws more current when getting hot.
Compare the resistance of the secondary output winding of each transformer on the inverter board. The tolerance can not exceed 3% of each other.

[Andrew F. Ali]

Re: RCA 46LA45RQ no backlight

Since the back lights come on for the first minute or two and then go out, I rule out capacitors. My bet is on a bad transformer or a bad bulb, some component that draws more current when getting hot.
Compare the resistance of the secondary output winding of each transformer on the inverter board. The tolerance can not exceed 3% of each other.

My bad....Some how missed the came on and shut off part.....NO not fuses...but CapLeaker set you in the right direction...Thanks