Toshiba 58L135UC Power issues

[cperiuta]

Hello to all

I have a Toshiba 58L135UC with no backlight, no power light and no display

I've verified the voltage off of the big capacitors C1A and C1B, it has 389.7V when P802 is connected and 146V with P802 unpluged. I think this is correct.

I have 5V output to main board, but not 12V output.

PWON has 3.1 V when I plug the TV, no change if I turn on. Can be a problem with power button?

Can somebody help me here?

Thanks for any help.

[budm]

Re: Toshiba 58L135UC Power issues

The 12VDC is generated by transformer T1, this power supply is turned on when the PS-ON present which you have because you are getting the 389VDC (PFC Voltage booster is OK) on the main filter cap.
Please check out the blue cap C113 which is next to transformer T1, I cannot read the print on the body to find out what the capacitance and the Voltage rating of the cap is.
Toshiba 75035342 Power Supply LED Board for 58L1350U
Pictures provided by shopjimmy.
BTW, your TV is Toshiba 58L1350UC, right? Not 58L135UC.

[cperiuta]

Re: Toshiba 58L1350UC Power issues

Yes, you're right TV model is Toshiba 58L1350UC. Here is the cap C113 print info.

Thanks

[budm]

Re: Toshiba 58L135UC Power issues

OK the cap is 0.027uF 5% Tolerance, 800V rating.
The body looks very uneven, you need to check its capacitance to see if it is OK, you will have to check it off the board.

[cperiuta]

Re: Toshiba 58L135UC Power issues

This cap is good, it shows 27.05nF.

Anyone have a spec sheet or manual for this power supply?

Thanks

[budm]

Re: Toshiba 58L135UC Power issues

OK, so it looks like the circuit is not active, we need to get the P/N of the SMD SMPS IC U1 so we can find out if it has VCC to run the IC or not.
That IC U1 drives the power MOSFETs Q101A, 101B which drive the power transformer T1.

[cperiuta]

Re: Toshiba 58L135UC Power issues

Here is the P/N of U1

Thanks a lot for you're help!

[budm]

Re: Toshiba 58L135UC Power issues

Good picture! Can you please do straight shot of that section with good clear focused like that so I can see how the traces are connected to the IC? It looks like the capacitor C7 is the filter cap for the IC VCC.

[cperiuta]

Re: Toshiba 58L135UC Power issues

Voila!

[budm]

Re: Toshiba 58L135UC Power issues

OK, found the spec sheet for SSC9522S, made by SANKEN.
Pin 2 is the VCC, pin 4 is the GND.
So look at the picture I marked, you can make the measurement from the top of the board, black probe on either JUMPER J19 or J30 (BE REAL CAREFUL, THESE JUMPERS ARE AT LINE DEADLY POTENTIAL!), the the RED probe on pin 1, 2, 3 of Q731 one at the time to take the DCV readings after the power switch is turned on.
Q731 and Zener ZD731 is the switched Linear regulator to supply regulated Voltage to the VCC to pin 2 of the SMPS IC U1. Opto couple PC902 is turned on by the PS-ON which in turn turns on the Q731.
C7 is not the filter cap for the VCC for U1, found that out after tracing the board.

[cperiuta]

Re: Toshiba 58L135UC Power issues

I read the same voltage before and after pushing the power button

3 - 18.35v
2 - 14.79v
1 - 14.11v

That means we have 14V to VCC pin on U1 and it doesn't goes thrue U1, right? Can I test the U1? Could be a problem on the power swich circuit too?

Thanks

[budm]

Re: Toshiba 58L135UC Power issues

According to spec of U1, VCC(on) is 11.80 VDC (typ.) so it has enough Voltage (14.11 VDC) to run.
So the next pin we need to check is the DCV on pin 1 (Vsens) of U1, it needs to be >1.42 VDC for the IC to run, so black probe still on jumper J19 or J30, then red probe on jumper J26.
BTW, did I already ask you to check the Rectifier DIODE D401A/B, and Dual diode Common Cathode D201 to make sure they are OK?

[cperiuta]

Re: Toshiba 58L135UC Power issues

J26 -- 1.68V
D401A/B are ok

How could I test D201?

[budm]

Re: Toshiba 58L135UC Power issues

J26 -- 1.68V
D401A/B are ok

How could I test D201?

OK, that Voltage is good.
D201, you will test between either one of the outer pins (the two outer pins are connected together by the trace) and the center pin.

[cperiuta]

Re: Toshiba 58L135UC Power issues

Outer pins comes from T1 and they are not connected together. That is like we have two diodes, right? These are the 12V otlet from T1? Do I have to remove D201 from the board to test it?

Thanks

[budm]

Re: Toshiba 58L135UC Power issues

OK, this one is set up as full wave rectifier instead of half wave recticier with two diode connected in parallel.
So just check it like two diode, the center pin is just the common Cathode.

[cperiuta]

Re: Toshiba 58L135UC Power issues

D201 is not good. I'll try tomorow to find it. Thanks

[budm]

Re: Toshiba 58L135UC Power issues

D201 is not good. I'll try tomorow to find it. Thanks

What did you find wrong with the Diode?

[cperiuta]

Re: Toshiba 58L135UC Power issues

I was wrong... I tested it again, it is OK, it gives 0.273V one way and OL on the other. What should I check now?

[budm]

Re: Toshiba 58L135UC Power issues

Well, the SMPS IC is getting the correct VCC and correct Vsens, so the only thing left will be replacing the IC, we do not have the diagram of the board to dig deep into details of the circuit to do more in depth trouble shooting.
You may be better off to get the new power supply board.
Another thing that bother me about the main board in post 1:
'PWON has 3.1 V when I plug the TV, no change if I turn on. Can be a problem with power button?' This signal is not changing the condition, so you may have more than one problem, this signal should toggle when you activate/deactivate the power switch.
What is the back history of this TV?