Rca led50b45rq

[x_orange90_x]

Re: Rca led50b45rq

I will check those pins tonight. However, i think i may have overlooked a very possible sign of failure.. I was going back through the pictures i posted earlier this week and found a great deal of discoloration around the resistors on the bottom of the board (picture reattached). From what I've read about this model, it doesn't usually run hot, so could this be a possible sign that the resistors are blown?

[x_orange90_x]

Re: Rca led50b45rq

Sorry for the delayed feedback. Here are the readings from the IC. I didn't have time to write the corresponding names out for each pin, so please refer to the attached picture.

1 - 0
2 - 0
3 - .49
4 - 0
5 - 0
6 - 0
7 - .62
8 - 0
9 - 0
10 - 0
11 - 0
12 - .28
13 - 0
14 - 0
15 - .22 drop to 0
16 - .11 drop to 0

[x_orange90_x]

Re: Rca led50b45rq

I finally got enough time to type this back out with the corresponding labels.

CSS - 0V
DELAY - 0V
CF - 0.49V
RFmin - 0V
STBY - 0V
ISEN - 0V
LINE - 0.62V
DIS - 0V
PFC_STOP - 0V
GND - 0V
LVG - 0V
Vcc- 0.28V
N.C. - 0V
OUT - 0V
HVG - 0.22V spike, drops to 0V
VBOOT - 0.11V spike, drops to 0V

[dick_barton]

Re: Rca led50b45rq

The first thing to note is that VCC is at 0.28V so this chip will not operate. Need to find out why there is no voltage supplying VCC

Are you certain that you have taken the readings with the set switched on and the black meter lead connected to the EC1 / EC1A ground.

[x_orange90_x]

Re: Rca led50b45rq

Set was out of standby (ON), and black probe was on the negative leg of EC1.

[x_orange90_x]

Re: Rca led50b45rq

Am i possibly checking this incorrectly? The lack of replies has me wondering if I've either stumped the experts, or just hit a dead end. This leads me to ask if the grounds behind the power board screws are a determining factor Here, because i am checking these voltages with the board breadboarded..

[budm]

Re: Rca led50b45rq

Am i possibly checking this incorrectly? The lack of replies has me wondering if I've either stumped the experts, or just hit a dead end. This leads me to ask if the grounds behind the power board screws are a determining factor Here, because i am checking these voltages with the board breadboarded..

Right now you will have to trace out the connection from the VCC pin of the PFC IC back to the switched power supply source which means reverse engineering the board, so how much time are you willing to spend to do that? I do not have the board in front of me to do that at this point.

[x_orange90_x]

Re: Rca led50b45rq

I will look closer at it tonight and try to follow the trace. Hopefully I'll get lucky and it lead back to a capacitor. I'm assuming that the VCC is one of the most crucial points of the power supply system?

[budm]

Re: Rca led50b45rq

No VCC no running circuit, just like no battery to run your cell phone.

[budm]

Re: Rca led50b45rq

We are going to need real hi res straight shot pictures of the top and bottom side of the board without all that glare so we can easily see the traces.

[x_orange90_x]

Re: Rca led50b45rq

Here is the best i could do without creating a glare again.

Edit: I added a couple more pictures with light shining through the board from both sides. PIN 12 (VCC) is the pin that lines up exactly with the left side of C4 (fourth pin from the right).

[budm]

Re: Rca led50b45rq

Check DCV at Collector of Q10.

[x_orange90_x]

Re: Rca led50b45rq

Thank you for the diagram! Do i just need to check the points you've labeled + and -?

[vinceroger69]

Re: Rca led50b45rq

q10 budm has maked check the dc voltage on the pin marked c thats the collector pin.

[x_orange90_x]

Re: Rca led50b45rq

q10 budm has maked check the dc voltage on the pin marked c thats the collector pin.

Am i putting the black probe on the - pin he marked as HGND and the red probe on that C pin? I really am trying to keep up with this, however my experience with electronics diagnostics has never went this in depth. I am completely willing to learn though and rather excited to be doing this.

[vinceroger69]

Re: Rca led50b45rq

yes i would test it that way myself just be carefull as thats the hot/mains live side of the psu so dont let probes etc slip as may cause more damage

[budm]

Re: Rca led50b45rq

Am i putting the black probe on the - pin he marked as HGND and the red probe on that C pin? I really am trying to keep up with this, however my experience with electronics diagnostics has never went this in depth. I am completely willing to learn though and rather excited to be doing this.

Black probe on HGND (HOT SIDE CIRCUIT GND), just be real careful since you are working in the deadly side of the circuit, best to at least plug the TV into the GFCI outlets.
E = Emitter
B = Base
C = Collector

[x_orange90_x]

Re: Rca led50b45rq

Black probe on HGND (HOT SIDE CIRCUIT GND), just be real careful since you are working in the deadly side of the circuit, best to at least plug the TV into the GFCI outlets.
E = Emitter
B = Base
C = Collector

Here are those voltages:

B - 13.5v
C - 14v
E - 12.97v

[budm]

Re: Rca led50b45rq

Here are those voltages:

B - 13.5v
C - 14v
E - 12.97v

So that Q10 Emitter has about 13VDC, but you are getting only 0.28V ON PIN 12 of the PFC IC.
As you can see in the picture that I marked, the E is conected ZERO resistor, another end of that resistor should be connected to pin 12 where C4 is also, so verify if my tracing is correct or not. It should show <1 Ohms between pin 12 of the IC and the Emitter/ or the resistor connected to the Emitter of Q10.

[x_orange90_x]

Re: Rca led50b45rq

Your tracing appears correct. I checked resistance between the resistor 000 and pin 12, from 000 to both sides of C4, and also from the incoming side of 000 to both ends of C4 and to pin 12. I get a reading of 1 with all of them, however a couple of times i had it bounce all around from 70.0 and below when checking the incoming side of 000 to the outgoing side of C4.