Telefunken 32" LCD TV Model TLCD-32HDA

[angelos]

Hi all,
I battled on this set all day and was none the wiser and thus need expert guidance.

Upon opening the set i noticed it was tampered. The plug wires were soldered direct into the board but for now i won't know if they're a problem. The symptom is that there is no back lights. Flashlight on screen shows the LCD has a picture. I checked the ballast inverter and noticed the following....
The drive voltage is not enough to start the lamps. I used my 100x scope probe to check whats happening. The drive IC is outputting a waveform as follows check "at_first_Xfmer_from_IC.jpg" measuring about 22Vp-p at a frequency of 250KHz. From there i scoped "From_collecor_of_mosfet.jpg" it was about 400V p-p and then i finally took my measuremet at the point where the output goes to the little board that expands the HT to the lamps. At this point my peak to peak is about 250V. Too little to strike the lamps on.
I added a rough sketch showing the circuit without the support components.
With the lamp tester the lamps light up even though this is not a fool proof method of testing them. I can get no info on the drive ic which is a F0711.
Surely the voltage on collector should have gbeen a lot higher on the mosfet where i measured but its not.
I also added a short video to show you what the ballast waveform does on switch on at https://youtu.be/ZVgnLDt__Uk
Can any body guide me better????

Regards
Angelos

[budm]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

1) When you first turn on the TV, do see the backlights even flash on for seconds?
2) Do you have about 380 ~ 400VDC when measure right between the two legs of the main filter cap?
3) Do you have Bl-on and Dim control signals from the main board.
4) What are the Voltages on each pin of the power supply connector that goes to the main board when TV is off and when power switch is activated? Your pictures are not clear enough to see if the pins have pin labels for them or not.

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

1) When you first turn on the TV, do see the backlights even flash on for seconds?

No not even an attempt to startup.

2) Do you have about 380 ~ 400VDC when measure right between the two legs of the main filter cap?

Nope on standby this voltage is 334V DC and when i press standby the voltage drops to 257V DC. I guess this means my PFC circuit is fubar.
I guess i will have to check that first before commenting on other tests.
Thanks Budm. Will check what drives that circuit but my knowledge on that circuit is rather limited.

3) Do you have Bl-on and Dim control signals from the main board.
4) What are the Voltages on each pin of the power supply connector that goes to the main board when TV is off and when power switch is activated? Your pictures are not clear enough to see if the pins have pin labels for them or not.

[budm]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Even if the PFC not working the DCV on the cap should not even drop down to 257VDC!, you should check the condition of that main filter cap.

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Will do. Tomorrow then.

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Hi Budm, looking at how power factor correction is implemented i realised that i might have misinformed you a tad. I measured that smoothing cap voltage across the full wave bridge rectifiers positive and negative output and not directly on the cap. Once i get to it in about 9 hours from now i will post a full update. Sorry for that.

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

1) When you first turn on the TV, do see the backlights even flash on for seconds?

No, nothing at all.

2) Do you have about 380 ~ 400VDC when measure right between the two legs of the main filter cap?

On standby it is 342V and when switched on goes to 391V

3) Do you have Bl-on and Dim control signals from the main board.

I get BK-ON = 4.43V and
ADJ = 5.15V
I must say that this set was tampered and all these wires have been soldered into the board directly bypassing the plug terminal. Afraid to swap those two wires around (BK-ON and ADJ).



4) What are the Voltages on each pin of the power supply connector that goes to the main board when TV is off and when power switch is activated?

On Con 3 we have

Standby ON
GND = 0 0
ADJ = 1.7 5.2
BK-ON = 0 4.4

On Con 2 we have

Standby ON

PS-ON = 0V 4.5V
+5VSB = 5.2V 5.2V
GND = 0V 0V
GND = 0V 0V
+5V = 1.96V 5.2V
+5V = 1.96V 5.2V
GND = 0V 0V
GND = 0V 0V
+12V = 0V 11.19V
+12V = 0V 11.19V

Now i noticed the +12V rail is at 11.19V, a bit low so i check the two electrolytics.
They were as follows

Capacitance ESR
1043uF 0.03ohm
1038uF 0.04ohm conclusion, no problem with them since both caps are rated at 1000uf 25V
That 12V circuit comes off the T301 transformer that also drives that inverter transformer. It goes to a TO-220 package double diode then thru a small coil t then to that 1000uf cap then again through a coil and then again through another 1000uf cap and then to the output pin of PSU



Your pictures are not clear enough to see if the pins have pin labels for them or not.

I have added some more pictures to this post.

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Any info budm?

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Any help? This thread has died?

[budm]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

So we will have to concentrate in the inverter section next since all the running Voltages and the commands signal are OK.
So that 40-pin? IC (I cannot read the designator as printed on the board only has 'F0711' I expect more than one lines printed on top of that IC.
Can we get close up pictures of the IC?
How about the P/N of the inverter transformer, and the resistance reading on the secondary side of the inverter transforner?

[angelos]

Re: Telefunken 32" LCD TV Model TLCD-32HDA

Please check this thread in 2 days from now. I am away at the moment and will upload the info as soon as i have returned.