Dead Vestel 17IPS71 power board

[dick_barton]

Re: Dead Vestel 17IPS71 power board

The initial voltage on the VDD capacitor (VCC I kept saying above) is initially derived via the internal circuitry of the IC from the voltage at the HV pin. When the voltage on the capacitor reaches a set point (data sheet) then the internal circuit switches off and allows feedback from the transformer (N3 winding) to maintain that voltage.
There are quite a few capacitors on the VDD input and the electrolytics are the ones that tend to fail. They may not lose their value but their internal resistance increases (ESR).

It is also worth checking D20 is not short circuit.

Do you have any voltage at the VDD pin. Don't forget to use the HOT ground and not chassis to measure the voltage.

[JonathanAnon]

Re: Dead Vestel 17IPS71 power board

The initial voltage supplied to the capacitor is derived from the voltage at the HV pin which supplies 1.2mA to charge Vcc capacitor.

Hi Dick, thanks for your response. I was actually pretty hopeful that it was going to be an issue with the startup capacitor, and that I would just have to replace that, but it and the other surrounding caps are all fine. Measured them off the board.

It is the part above that is key I think. Are you saying that internally in the chip it derives the voltage and feeds it to pin 6? And I guess from that then I could extrapolate that if I have voltage on the HV pin and nothing on pin 6 then the chip itself is cooked?

[dick_barton]

Re: Dead Vestel 17IPS71 power board

Also check any capacitor(s) connected to the VCC supply since they tend to go faulty.

[dick_barton]

Re: Dead Vestel 17IPS71 power board

At startup the capacitor connected to the VCC input starts to charge and should reach 16V. This voltage should not fall below 10V during the startup sequence as given in the data sheet for the FAN6300.

The initial voltage supplied to the capacitor is derived from the voltage at the HV pin which supplies 1.2mA to charge Vcc capacitor.

When the voltage across the capacitor reaches 16V the IC drives the mosfet driving the transformer and a secondary winding on the transformer then feeds back voltage to maintain the voltage at VCC capacitor.

[JonathanAnon]

Re: Dead Vestel 17IPS71 power board

OK update on this dead board, replaced ic FAN6300 and board is now powering up with several output pins now reading 12v, no output voltages were present on this board before.

Hi guys, very interesting to read the thread. I have the same board with the exact same issue. Voltage on the HV pin and nothing on the VDD pin.

The schematic that is included at the start of the thread is the only one that I can find for this board, but it is different. R294 simply does not exist on my board, and there is no connection at all from the main filter cap to the VDD pins through dropping resistors.



The only feed to the startup cap that I can find is from the winding on the primary side of the transformer. The TV is worth nothing but it's bugging the hell out of me, so I'm going to try and replace the PWM chip and see if that makes it power on again.

[Hamie]

Re: Dead Vestel 17IPS71 power board

If the fuse is open and Q15 tests good check LF2

[kimb]

Re: Dead Vestel 17IPS71 power board

Hello. I just had one of these in. Not a simple one so I did all the suggestions on here. Really hard in my case as everything looked like it was working, but it didn't switch on. 5v to sensor , 12v and @25v off the rails etc but still no start. Very odd. The power worked but would not start up. Feed power to the backlight works. So must be the media board. I advised the customer that it was uneconomical to repair as this TV is worth less than the part. Wished I could fix it but no go. So not always the power board. I hate saying this as it just makes fixing these even more complicated. HTH. Kim

[rtstorm]

Re: Dead Vestel 17IPS71 power board

Also i have discovered that Q17 are shorted (i unsolder it and then it was no short on )

[rtstorm]

Re: Dead Vestel 17IPS71 power board

Hello, i have the same Vestel 17IPS71 board. TV wont start, no led blink (i have 5V on LED diode). I check all diode and they are ok (on secundary) form one set of diodes i het 12V but from another i her 30V. I can hear high pitch noise from board.
The caps look ok, no leak or bulb. What else can i check?

[Calderon]

Re: Dead Vestel 17IPS71 power board

Hi, i have Finlux TV with this same powersuplly, measured between q17 drain and source and its shorted? Also when this is plugged in i hear very high pitched noise going louder about 2 secs and then silence for 3-4 sec and again, as itś trying to start or something.. this comes from the powerboard..?

[Joba01]

Re: Dead Vestel 17IPS71 power board

Hi guys, thanks a lot for all the descriptions, it already helped a lot to understand the process and common falts. I have the same vestel board in a 'Telefunken' TV. The standby LED on the front is blinking. I tried all measuring than you described. On the CN4 output connector I read the 12 volt but I don't get the 5v standby voltage, any guesses what could be wrong? I also read 2.5v on pin7(the 4th pin in the upper row, starting from the pin that is marked as 1 on the board). I could't find a shorted diode, I still changed d22, d24 and d26 but that was more like last resort . The mosfet is a FDD120AN15A0, I tried to measure the DC voltage to ground it was 34v between source and drain and 34v between gate and drain, not sure how to interpret that. Hopefully you guys have a hint, best joba

[vinceroger69]

Re: Dead Vestel 17IPS71 power board

q17 yes thats the one i thought may of been the led driver mosfet but dick-barton mentioned it maybe q15 which is on the top side of the pcb under a black heat sink i think
this guide may help you
https://www.youtube.com/watch?v=RkWy1EirEu8

[fnets]

Re: Dead Vestel 17IPS71 power board

ok thanks

this is q17



should I test this? (if so how)

[vinceroger69]

Re: Dead Vestel 17IPS71 power board

on the board you have printing by each component q15 is the a reference designator, we think its the led driver mosfet you have been asking about earlier in the thread q basically means transistor like c then a number means its a capacitor r then a number is a resistor this link is quite good.
https://electronics.stackexchange.co...-markings-mean

[fnets]

Re: Dead Vestel 17IPS71 power board

can I ask what q15 means?

[vinceroger69]

Re: Dead Vestel 17IPS71 power board

I think your mosfet to check out is Q15. Hard to tell from the pictures.
Check all the diodes around the FAN IC and the Mosfet

The pictures in post 2 are zoom able and clear i first thought q15 then edited my post as wasnt really sure

[dick_barton]

Re: Dead Vestel 17IPS71 power board

I think your mosfet to check out is Q15. Hard to tell from the pictures.
Check all the diodes around the FAN IC and the Mosfet

[vinceroger69]

Re: Dead Vestel 17IPS71 power board

I hope we can both learn something from this.

Here's my board



ic probably on the underside?



how do I test this? (also what does an led mosfet look like?)

led mosfet i think maybe q17? bottom side of board hopefully dick-barton will advise although i think your issue maybe that fan6300 ic i sent the ebay link for

[fnets]

Re: Dead Vestel 17IPS71 power board

help has been fantastic, thank you.

Have ordered a new FAN6300A

this is tiny, any advise on replacing.

[vinceroger69]

Re: Dead Vestel 17IPS71 power board

Thanks dick-barton you have more experience than i have in repairs, i did advise to replace that ic and added a link, but he could not find it on his board? hence i asked for better pictures so we could point out the ic.