Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

[ray14324]

Hi everyone,

Searching the forum revealed loads of issues with this type of power supply board however I could not find a solution to my issue from them. Excuse the "another Vestel" thread

The full story was: my Telefunken TV did not have a standby red light after of series of power outages in a couple of minutes. Sadly in my rural city the only technician that fixes TV's is away these days as I cannot reach him by phone. I want to try to have a go at it (with the internet's help).

Reading into this symptom the general consensus was that either the power board or the logic board is faulty. Trying to see if its the power board i tried to measure the standby voltage, which should be available when power is applied. From the schematic i believed it was +5V_STBY, dc from connector CN4. The ground lines were identified with the multimeter in continuity mode (to not make measurement mistakes regarding pins). All voltage measurements gave 0V (or close to 0V). Thus i believe the power supply truly is at fault. I tried seeing who produces this signal however from the actual board it can be seen that it is omitted (Investigation_1.png attachment). The part in the attachment is the only one i see though that produces it. This is where I'm confused and stomped. Where should I check next ? Are my actions above correct or wrong ? Could you please help me with some future steps ?

User question: could I replace the board with a similar one that respects the output connector or will it not work ? Searching for it gave many different kinds of boards (visually slightly different component-wise) however they were sorta paired with another code so I thought you might need to respect the LED panel.

[cheeky2]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

Check the soldered fuse red circle.
Check the mosfet oblong shape in red isn't shorted.
If you wish to order a replacement psu then you will need to match the left hand number on the blue oblong highlighted area 23117579 If you don't then your TV will unlikely operate correctly
Download the manual for it in plenty of other threads for the repair of this psu and find out if the fuse has gone what components shorted out.

[ray14324]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

Thank-you kindly for your help and guidance.
With power not applied to the board and the multimeter in continuity mode I checked the mentioned fuse (FS100 in schematic). It was ok (it beeped).

I moved on to the N channel mosfet (Q301), after looking up the model , with the multimeter in diode mode I checked between S-D (more details in the attached PNG file). It gave good readings (0.544 red probe on S, black on D and no reading when reversing)

In that area I read that further tests can be made on the mosfet (apply power on Gate to open it then verify if it is opened) but my understanding is that I have to take it out of circuit ?

I also found a thread that indicated towards checking the resistor R320 from the source. Should I check that as well ?

Much to my surprise I found little (to none) places where I could buy a replacement one with the mention part number. Since I am not from this field of expertise might some of you know such an "aliexpress" place on the internet ?

[dick_barton]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

If Q212 is not fitted ( in your photo in post #1 it is not) then the 5V_STBY is probably generated by the mainboard and sent back to the power supply.

I think the +12V supply should be running. Check the voltages on U202 using the negative leg of C103 as the ground point for your multimeter when making the measurements, very carefully. Do not let the multimeter probe slip.

[ray14324]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

Thank-you kindly for further advice.

Upon inspecting the datasheet of U202, it specifies that VDD is an output DC voltage. I proceed to measuring that. Upon measurement I received variable readings over time (made sure not to move and held breath) on the multimeter (the zip archive).

Is it ok though ? since its a PWM controller the output voltage is supposed to vary in my opinion.

Is there anything I could check further on U202 ? I looked at other outputs but I could not understand what values I should look for. Do the results seem off ?

[dick_barton]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

VDD is initially charged via the voltage to the HV pin and once it reaches 15.5v the PWM controller should be working and the gate output should be driving the mosfet which in turn oscillates the transformer and a feedback winding then supplies the voltage to the VDD pin to keep it running.
Your video is showing the initial voltage exceeding the required start up voltage.

Check D214, D215 , D517 (if fitted) and also the capacitors connected to VCC_M

[ray14324]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

I see, so the voltage measurement should be steady, now its just turning on then turning off in a loop.

I measured the diodes (D517 isn't present) they seem ok (D214-215.png).

I went to measure the capacitors. Took C207 from the board. You can see the measurement in the video (C207-Measurement.zip). From my understanding this seems faulty as the charts indicate a maximum of 0.56 ohms (47uF-63V) while I get over that. Multiple readings are inconsistent as well. Am i right or was it something I did wrong ?

Thank-you kindly for your guidance in this.

[dick_barton]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

The maximum 0.56 ohms you mention would be the ESR (electrical series resistance) value. An ESR meter would be needed to measure this value not a multimeter set to ohms.

[ray14324]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

After ordering new capacitors and testing them out I found out that the digital multimeter wasn't set to the highest resistance (in the video the knob was set to 200k when it should have been set to 2M). Setting and rerunning the test on each capacitor get below 0.56 initial readings => the initial capacitors were fine.

I still had them replaced since i did unsolder them off the board to test them but the problem hasn't disappeared. Still getting the fluctuating voltages on VCC_M both measuring at the cathode of D214 and D215 (while having the black probe on ground, negative leg of C103) and on pin 7 of U202.

Is there anything else I can check or where to look ?

[ray14324]

Re: Telefunken LED TV with no standby linght equipped with Vestel 17IPS20 PSU

The maximum 0.56 ohms you mention would be the ESR (electrical series resistance) value. An ESR meter would be needed to measure this value not a multimeter set to ohms.

Because I was probably writing that post in that time I did not see your reply. I'm terribly sorry. Also feeling embarrassed because I did not know understand that the multimeter needs that feature. However having replaced them with new ones (hopefully good also) it leaves the impression that the issue lies before that entry point. Does U202 only handle DC ? (might have to probe the other pins ?)

Because I don't have the tools to properly test caps and the issue is significantly different from what I found written here I'm begginning to think my options are to wait for the technician to be back (1 more week) or buy a new PSU (sadly this model is really rare which I don't really understand being a turkish brand board).