Proscan 50" PLDED5066A-E no backlights

[budm]

Re: Proscan 50" PLDED5066A-E no backlights

OK, so your meter probably was not fast enough to catch the Voltage rise before it goes into protection mode and lead to believe that the problem is in the power supply section but turns out to be bad LEDs just like other LED Backlights TV. At least now you found out you do have bad LEDs.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

First I would like to thank everyone for the help. Update!! Apparently when I tested each LED in the strip I missed the first LED in each strip. I bought a power supply and tried to test each pair of wires with 45 DCV. I got nothing so I broke down and removed all of the strips from the tv. On all five strips the first LED is bad. The back of the strip under those LEDs are burnt. Sorry for the confusion.

Is there a way to remove the LED and replace those that are bad. The strip is around 25 each and the tv is not worth that much but I do have LED strip from another tv if there is a way to remove.

[CapLeaker]

Re: Proscan 50" PLDED5066A-E no backlights

good, now we know that the problem has to be on the PSU.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

5 X 14. I connected two AA batteries and checked each light individually. They all worked.

[paulstef]

Re: Proscan 50" PLDED5066A-E no backlights

Is there a way to test the LED strips without taking the panel off. If so how. Thanks again for all the help.

It would be really helpful to have an oscilloscope. Sometimes there is voltage for the LEDs just for a brief moment, the power supply recognizes there is a problem and shuts down the driver circuit. That's something you may not be able to detect using a multimeter.

I had to repair several backlights of these cheap TVs. The problem is we don't know what's their backlight configuration. I would say you may have 5x 10 to 5x15 LEDs in series (inside the panel) which are then all in series on the PCB.

So you could remove the connector that goes to the LEDs and try to start with 25V on each of the output pairs. Assuming there are 5 strips in there it's not likely that ALL strips are damaged. So you should get light on at least one of them. If you don't get light on any of them you may slowly increase the voltage. Make sure to use a benchtop power supply with current limit set to let's say 300mA.

[CapLeaker]

Re: Proscan 50" PLDED5066A-E no backlights

That's where the min /max setting on the DMM comes in handy.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

C9F=.661
C8F=.669

I only have a DMM but I took pic of the screen with a high speed camera on my phone while turning on. The voltage when turned on jumps to 1.8 volts them drops to .66 volts.

[budm]

Re: Proscan 50" PLDED5066A-E no backlights

OK, I want to be sure about this Voltage measurement I asked on post 41:
'What DCV do you have between the two legs of the brown cap C8F, and between the two legs of brown cap C9F?' and you report the reading of 0.661V between the two legs of C9F.
What I forget to ask you to do is to leave the probes on the legs of the cap, plug the TV into the outlet and then turn the TV on to see if you see the Voltage jumps up on the meter (set the meter to 200vdc scale) or not.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

All of the wires of the female connector to chassis ground were OL

[budm]

Re: Proscan 50" PLDED5066A-E no backlights

I have no idea, I upload the spec sheet but it does not have application sample circuits to show how it is used. Need to locate application notes, will have to do more searching for it.
BTW, remove the LED female connector from the board and then check each pin of the female connector against chassis GND to see if any one of them show resistance or not.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

Pic of the IC

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

If there is a lock our curcuit, which pin on the IC would it connect too and I will try and trace it.

[budm]

Re: Proscan 50" PLDED5066A-E no backlights

Since we do not have the diagram, then I do not know if there is any lock out circuit to not allow the IC to drive the Gate drive isolation transformer.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

I traced pin 17 and pin 18 to T1F. Is there any faults that will stop the voltage from reaching pin 18 and 17 other than the IC itself?

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

Should the other pin 5 thru 18 read in mV ?

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

No scope so I will try and locate a IC

[budm]

Re: Proscan 50" PLDED5066A-E no backlights

So Pin 2 (STBY ON/OFF) is getting the ON command and VCC is OK, but no action on the output pins.
You need to probe the pins with the scope or just try replacing the IC.

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

Q7F is left of pic

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

Q7F is top of pic

[mnpdreed]

Re: Proscan 50" PLDED5066A-E no backlights

IC1F
1 VCC 11.10V
2 STB 4.13V
3 GND
4 RT 1.487 V
PINS 5 thru 18 reads mV

Question. Q7F runs off pin 1. The 3 pins of Q7F read 11v
11.10v, 11.79v, and 11.80v. Is this normal?