TCL 65S517 No Backlight, Picture and Sound OK

[budm]

Re: TCL 65S517 No Backlight, Picture and Sound OK

TS3 is the Gate drive transformer for driving the MOSFET's QW3, 4.
The primary side of TS3 is driven by that LED driver IC U601. I would not remove TS3 at this point.

Need to look up the specsheet of U601 to locate the VCC pin and ENA pins to find out what Voltage it has on those pins.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

TS3 is the Gate drive transformer for driving the MOSFET's QW3, 4.
The primary side of TS3 is driven by that LED driver IC U601. I would not remove TS3 at this point.

Need to look up the specsheet of U601 to locate the VCC pin and ENA pins to find out what Voltage it has on those pins.

OK will do, I checked the pins LED driver pins at the plug and with the set on and showing picture but no backlight I am getting no voltage on any of those pins. I am going to look up the sheet on U601 and check those pins

[nomoresonys]

Re: TCL 65S517 No Backlight, Picture and Sound OK

It's going well, looks like you have isolated the issue to the powerboard.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

TS3 is the Gate drive transformer for driving the MOSFET's QW3, 4.
The primary side of TS3 is driven by that LED driver IC U601. I would not remove TS3 at this point.

Need to look up the specsheet of U601 to locate the VCC pin and ENA pins to find out what Voltage it has on those pins.

I pulled the spec sheet. I see the ENA pin, but which would be considered the VCC pins? Would it be one or both of those top driver pins? Sorry I dont read a ton of schematics. Mostly only on Pinball Machines.

[budm]

Re: TCL 65S517 No Backlight, Picture and Sound OK

So what is the P/N of the IC?
Vin = vcc

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

OZ9976AGN
Intelligent Lighting
Offline LCD Controller

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

So what is the P/N of the IC?
Vin = vcc

So if I am testing this right as per the picture i drew on, neither of those pin have voltage. I was guessing that 1 on the board denotes 1st pin on that IC.

[R_J]

Re: TCL 65S517 No Backlight, Picture and Sound OK

If you follow the trace from pin 15, it connects to J5 & J43, that is ground. I would check pin3 for VCC and pin4 for enable (BL_on)
Check the voltage between hot ground (L602) and VBUS+ (L601)

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

If you follow the trace from pin 15, it connects to J5 & J43, that is ground. I would check pin3 for VCC and pin4 for enable (BL_on)

So if I read that right I get P3-12v and P4-3.2V. The pins I tested are noted on the pic.

[R_J]

Re: TCL 65S517 No Backlight, Picture and Sound OK

I think I spotted your problem... R649 (22Ω?) is blown/missing, it should be the same as R652. I suspect QW4 could be damaged as well

So you have good vcc and the enable is also ok, Check the VBUS voltage, careful this is the hot side of the power supply.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

I think I spotted your problem... R649 (22Ω?) is blown/missing, it should be the same as R652. I suspect QW4 could be damaged as well

So you have good vcc and the enable is also ok, Check the VBUS voltage, careful this is the hot side of the power supply.

Sorry the pic was kinda bad I guess. R649 is present and reads 22 ohm just like R652. I am not really sure where to check the VBUS voltage at and where to put my ground probe, Iam doing a few things I have never done yet here. Lead me there and I can test them.

[R_J]

Re: TCL 65S517 No Backlight, Picture and Sound OK

ok, it was just the picture. you can check the VBUS voltage between hot ground (L602) and VBUS+ (L601) But I suspect it is ok.

Then have a good look at C620 (or check it if you have a cap tester) This cap when bad usually bulges, but might not and could still be open, if it is open the circuit will not work because it is the ground return for TS2

One thing to check is the LED1+ voltage going to the led's, You must monitor this voltage as you turn ON the tv and see if there is any voltage present. If the led string is open, this voltage will come up fast and then drop to 0v due to the protection circuit. If you tried to check it once the tv was on and it check 0 volts, it may be due to open led's

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

ok, it was just the picture. you can check the VBUS voltage between hot ground (L602) and VBUS+ (L601) But I suspect it is ok.

Then have a good look at C620 (or check it if you have a cap tester) This cap when bad usually bulges, but might not and could still be open, if it is open the circuit will not work because it is the ground return for TS2

One thing to check is the LED1+ voltage going to the led's, You must monitor this voltage as you turn ON the tv and see if there is any voltage present. If the led string is open, this voltage will come up fast and then drop to 0v due to the protection circuit. If you tried to check it once the tv was on and it check 0 volts, it may be due to open led's

Checked the Vbus voltage and I get 396V between those 2. I desoldered the C620 cap. Im not really sure how to test one of these, I usually test the round electrolytics. I do have an ESR meter and a Klein DMM with capacitance but there is no farad values on the top of this cap. It doesnt look bulged but I cant find a video on how to test these that is in english.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

I think I found the Data Sheet. I decoded the cap to this line and it looks as if it should read .027uf. In capacitance mode on the meter it reads 26.96 nf so am I safe to assume it may be good?

[nomoresonys]

Re: TCL 65S517 No Backlight, Picture and Sound OK

That capacitance is ok.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

ok, it was just the picture. you can check the VBUS voltage between hot ground (L602) and VBUS+ (L601) But I suspect it is ok.

Then have a good look at C620 (or check it if you have a cap tester) This cap when bad usually bulges, but might not and could still be open, if it is open the circuit will not work because it is the ground return for TS2

One thing to check is the LED1+ voltage going to the led's, You must monitor this voltage as you turn ON the tv and see if there is any voltage present. If the led string is open, this voltage will come up fast and then drop to 0v due to the protection circuit. If you tried to check it once the tv was on and it check 0 volts, it may be due to open led's

I soldered that good cap back on the board today and checked voltage at the LED1+ when powering on. Voltage bobs around in the MV range a little then settles on 0.7 V. So not really any voltage spike to speak of.

[budm]

Re: TCL 65S517 No Backlight, Picture and Sound OK

Hi RJ, Do you have the link to that good clear pictures of the power supply board?
It is strange that the VCC pin does not match the app schematic of the IC.
At this point it looks like the IC is not driving the TS3 Gate drive transformer.

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

Hi RJ, Do you have the link to that good clear pictures of the power supply board?
It is strange that the VCC pin does not match the app schematic of the IC.
At this point it looks like the IC is not driving the TS3 Gate drive transformer.

Budm, Not sure if this will help but here is a link to the board on the web, and I have included new photos of my board that are about as bright and resolute as I can get them. Let me know if you I can help in any other way.

https://www.shopjimmy.com/tcl-08-l17...-supply-board/

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

Here is a better photo if you are trying to follow traces from the IC

[rebelkustoms]

Re: TCL 65S517 No Backlight, Picture and Sound OK

I think we may have run out of road on this one. I am out of ideas I may hunt around for a PS on ebay or something.