Diagnosis of a 40AO2USB TV that's stuck in Standby

[Varoshiotis]

Hi, this is my first post!
I have a Techwood 40AO2USB TV which when turned on flashes a blue led and then steadies this. I assume this is a Standby Mode. I can not make the TV do anything else (other than switch off - blue light flashes again and then goes off). I assume the TV goes through it's checks, then finds something that is not right and goes into Standby. Can someone please suggest what I should check/test to narrow down whether it is the PSU Board (markings: Vestel 17IPS20, 23250360) or the Main Board (markings 10099021) or the Backlight Assembly, OR something else. I have a Fluke Meter and I am competent in using it, and I am electrically-aware on safety. I am not after component identification & replacement, rather to know what replacement board to change without spending money unnecessarily. I can provide photos if helpful.
Thank you!

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

There are quite a few versions of the 17IPS20. What version number is given on your power supply.
Have you measured any of the voltages on the various connectors?

eg these are readings from another power supply as an example

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Hi, thanks for responding.

1. The markings on the PSU Board are: Vestel 17IPS20, 23250360 - 27447736 1006.

2. No, I have not taken any measurements as yet, but will do so once I have a table confirmed such as the one you suggested.

Thank you again!

https://www.badcaps.net/forum/attach...1&d=1603037237

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

The photo is too hard to make anything out. The black connector at the bottom right hand side has a parallel set of pins similar to the one I listed where you need to take the voltage readings.

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Thank you Dick_Barton.

I have taken some measurements from the black connector on the PSU feeding the MB. Unfortunately I do not have a drawing and so I don't know how the pins are numbered. And, I can only take the measurements from the six (6) outside pins of the connector as if I try to measure the voltage on the row of pins behind this I run the risk of shorting things out. I don't know if I pull the board out and see on the underside whether access is going to be easier! Anyhow, the Voltages on the 6 pins of the black connector to the MB are as follows (pins numbered 1-6, 1 top, 6 Bottom):

Pin 1: 11.97 V
Pin 2: 0 V
Pin 3: 0.112 V
Pin 4: 0.207 V
Pin 5: 1.984 V
Pin 6: 0.017 V

(I measured them a couple of times and they were steady at the above values). The TV was Turned ON, but again with the little blue led light steady ON (I assume this is Standby).

Does that tell you anything?
(I appreciate your help. If it helps I can post another photo of the PSU Board).

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

As I said earlier there are several versions of this power supply so a good high resolution picture could help to identify it.
Attached is one schematic but I don't know if it's for your power supply.

Can you match the connectors to the diagram?

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Thank you Dick-Barton

Yes, I have realised there are several deviations of the PSU Board. I have taken a few more photos, hope they have better resolution. There is a label on the last Photo (Bottom Right) reading: 071114 R9; does that mean anything to you?

Thanks again!

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

It looks as though it's possibly revision 9 so 17IPS20-R9
Unfortunately the pictures are still too small to make out any of the component labelling. Can you post a photo of the full board well focused.

The power supply schematic is within the attached manual

Take a look at the last page. If you have CN4 can you give the readings.

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Thanks Dick_Barton

I tried to reply twice and somehow managed to lose the response - I wonder if there is a time limit on response!)

Anyway, Yes, I think you are right - it is the 17IPS20 Revision 9 PSU Board.
Thank you for the Manual, I will study it. I am surprised that still you cannot see the photos with enough resolution - I have no difficulty doing so when I log onto the Website and read the Post. If allowed I can send the photos to you via an email?

I have located the CN4 Connector - it is the connector to the MB. It has 12 Pins. I have tried to sync these based on the 24V Rail: With the TV Upright (Normal Position), and with the CN4 Unplugged, and looking through the Opening I have labelled the Pins as follows:

Top:
Pin 11 Pin 12
Pin 9 Pin 10
Pin 7 Pin 8
Pin 5 Pin 6
Pin 3 Pin 4
Pin 1 Pin 2

I have taken two sets of Measurements:

1. TV Upright (Normal Position), ON Mains, CN4 Unplugged:
Pin 1: 23.46V Pin 2: 0 V
Pin 3: 0.001 V Pin 4: 0 V
Pin 5: 0 V Pin 6: 0 V
Pin 7: 0.046 V Pin 8: 0 V
Pin 9: 0.004 V Pin 10: 11.97 V
Pin 11: 11.97 V Pin 12: 11.97 V

2. TV Upright, ON Mains, CN4 Connected to MB:
Pin 1: 0.02 V P2: Not Measured (NM) due to risk of shorting Pins
Pin 3: 1.98 V P4: NM
Pin 5: 0.207 V P6: NM
Pin 7: 0.156 V P8: NM
Pin 9: 0.002 V P10: NM
Pin 11: 11.97 V P12: NM

I hope you can make some sense of these & thank you again!

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Is Q212 in circuit. If not then that would explain the missing +5V on Pin3.

The backlight control signal is missing (Pin5) that goes to the enable pin of U500 (Led driver circuit)
Can you check with a bright torch if there is any picture on the screen. Use the remote to go into menu and look carefully.

It's starting to look as though you may have a faulty led(s) or a faulty MP3394

[steviewonder]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Most likely Bad led's...Rather more likely than a psu issue,from experience with any IPS20 version...

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

That's my thoughts too.

Can you check what voltage you have at V_LED+ at switch on. The voltage will peak quickly then drop just as fast.

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

On Power Up I measured 104.5 V on the Pin with the White Wire out of the PSU Board going to the LEDs. As you say this then starts dropping.

I did try shining a bright torch on the TV - Nothing seen!

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

What did it drop down to?

It is looking more and more like a led(s) issue or led connection issue.

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Dropped to 0.1V over some 10-15 mins (and slowly continues to drop).

[R_J]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

On Power Up I measured 104.5 V on the Pin with the White Wire out of the PSU Board going to the LEDs.

This indicates to me that the led string is open, likely one ore more open led's

[arizanotlari]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Tv goes to standby mode? This is not led fault. Check mainboard first.

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

What is the voltage on pin 16 (VCC) of U500. It should be 6 Volts

You could test the backlights by disconnecting the mainboard from the power supply and connecting up the two resistors to CN4 as shown to provide backlight on signal which should be 1.6V or greater

[Varoshiotis]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

Thank you Arizanotlari & Dick_Barton for your suggestions.

Dick_Barton: I can't find U500 on my PSU Board! Am I searching in the wrong place or is my Board different to what you expected?

Also (and please excuse my ignorance), could you simplify your second point about connecting the two resistors to CN4?

(I do have a stand-alone Voltage Generator, and I can adjust Voltage & Current - could I switch the TV Off, disconnect the 2-wire connector driving the LEDs and apply a voltage to the two pins to test the LEDs? If so, what Voltage should I set?).

Arizanotlari: You suggest I check the MB: Any specific checks I should make?

Again, thank you both for giving up your time to guide me!

[dick_barton]

Re: Diagnosis of a 40AO2USB TV that's stuck in Standby

U500 according to the circuit diagram is the led driver IC and is probably on the underside of the power supply.
Disconnect the mainboard from the power supply.
Connect your power supply set to +5V and use a 1K resistor in series to connect to BL_ON-OFF (CN4 Pin 5) and the 0V to chassis.
Power on the set and your external power supply and see if the backlights come on and stay on.