No voltage cold rail. TCL L39B2610

[keshin]

Hey guys and gals quick warning I'm quite movie and have 3 LCD tvs I wish to learn this new skill on. I appreciate very much any help anyone can give me. That aside here are my symptoms.

1. The tv does not turn on, no standby led etc
2. The fuse was blown I have replaced and it has not blown again
3. I have taken voltages on different places and it appears I'm not getting voltage across to the cold side
4. No caps appear to be bulging or leaking
5. No other signs or burnt components or damage apart from pictured below slight deformed frame.



I'm thinking the problem lies somewhere at this transformer.I get voltage to the hot side but not out the cold side.



I appreciate any help anyone has to offer I'd like to learn the skills to repair this stuff instead of it ending up in a landfill. The worlds already full of too much waste

[attainteddragon]

Re: No voltage cold rail. TCL L39B2610

if your fuse failed then it is most likely that you have other bad components.

first, we need pics of the entire back of the tv and a straight on pic of the whole ps.

you also need to check what voltages are present on the harness that goes to the main board. list as pin no, pin desc, v in stby, v when on.

[keshin]

Re: No voltage cold rail. TCL L39B2610

Thanks for your reply attached are 3 photos one of while back of tv, main power board and then main board





As I cannot turn the tv on I can only give voltages with the power plugged in

Pin out as follows starting from top left
24v = 0v 24v = 0v
24v = 0v GND = 0v
GND = 0v GND = 0v
3.3v = 0v 3.3v = 0v
PS-ON = 0v GND = 0v
BL-ON = 0v DIM = 0v

[budm]

Re: No voltage cold rail. TCL L39B2610

Thanks for your reply attached are 3 photos one of while back of tv, main power board and then main board





As I cannot turn the tv on I can only give voltages with the power plugged in

Pin out as follows starting from top left
24v = 0v 24v = 0v
24v = 0v GND = 0v
GND = 0v GND = 0v
3.3v = 0v 3.3v = 0v
PS-ON = 0v GND = 0v
BL-ON = 0v DIM = 0v

Are those Voltage taken with all the cables back in place and measured before and after the power switch is activated (the Voltages after the power switch is activated are needed for us to find out if the main board sends out the command signals or not) ? We need those readings in two states.
This is an always on power supply so it should have some Voltages on the cold side.
We also need clear straight shot high res of the whole top and bottom side of the board so we can trace out the connections.

[attainteddragon]

Re: No voltage cold rail. TCL L39B2610

could you also check the voltage on ce1 or ce2. dcv across either of these caps. be very careful as you are measuring voltages on the hot side of the ps.

a picture of the underside of the ps will be required too.

if you can add pics as attachments, (by clicking on advanced then add attachment,) will make things easier to view in the thread and not slow down the loading of page.

[keshin]

Re: No voltage cold rail. TCL L39B2610

With cables plugged in voltages are 0 pushing power button does not change state or anything. Attached is a photo. The red circled section is the high voltage side which also has voltage. The green circled area is the low voltage (cold) side it has no voltage anywhere. The blue circled section starting form the top are as follows.



All tests on hot side used hot ground
All tests on cold side used cold ground

Voltage regulator
Hot side. Cold side
Pin 3 =0v. Pin 1 =0v
Pin 4 =0v. Pin 2 =0v

Transformer ? (Centre blue circle.
Hot side. Cold side
Pin1= 0v. Pin9= 0v
Pin2= 0v. Pin8= 0v
Pin3= 321v. Pin7= 0v
Pin4= 321v. Pin6= 0v
Pin5= 321v

3 blue caps
Hot side Cold side
Cap1= 0v Cap1=0v
Cap2= 104v Cap2=0v
Cap3= 104v Cap3=0v

[keshin]

Re: No voltage cold rail. TCL L39B2610

Sorry what does dvc mean? I'm still new to this. Attached is the back view

[budm]

Re: No voltage cold rail. TCL L39B2610

I need pictures as requested in post 4 for me to be able to help you.
BTW, you are using the wrong GROUND for your meter for those Voltages you report for the hot side.
No way you can have 482V reading without nice big smoke coming out from the TV, you use wrong ground for the Primary side, the negative leg of the main filter cap in the hot side is the ground ref point for the primary side circuit. Those readings are invalid.

[budm]

Re: No voltage cold rail. TCL L39B2610

Sorry what does dvc mean? I'm still new to this. Attached is the back view

DCV = DC Voltage
That is good picture, thanks.

[keshin]

Re: No voltage cold rail. TCL L39B2610

Sorry guys will try again with pictures also not sure if hot side measurements are right in my previous comment I tested with ac on the volt meter

Ce-1 = 323dcv
Ce-2 = 323dcv

Attached to this post is the front view

[keshin]

Re: No voltage cold rail. TCL L39B2610

I have updated the readings on the post #6

[keshin]

Re: No voltage cold rail. TCL L39B2610

Any help with this anyone?

[budm]

Re: No voltage cold rail. TCL L39B2610

https://www.badcaps.net/forum/attach...2&d=1504152366

Can you read the P/N of that 8-pin SMPS IC on the top left of the picture?
Check resistance of the MOSFET QW1 (attached to the heatsink) Source pin resistor R403 to see if it still shows < 1 Ohm or not, it looks like it has blown.
Also check the capacitance and ESR of the startup/running cap C424.