Dead Vestel 17IPS71 power board

[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?

[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 )

[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

[Hamie]

Re: Dead Vestel 17IPS71 power board

If the fuse is open and Q15 tests good check LF2

[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.

[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.

[dick_barton]

Re: Dead Vestel 17IPS71 power board

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

[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

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

[QUOTE=dick_barton;968967]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.[quote]

Is this common now? I haven't seen that before on any of the other TVs I've worked on. I guess I will know to look out for it now.

It is also worth checking D20 is not short circuit.

Yeah I checked it it's good. One bad diode on the secondary side but I got that sorted.

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

Yeah I always use the main filter cap ground as the ground for primary side measurements.

17ips71-r4.pdf
All I could find was the R3 version of this schema, which was what I was working from, but that seems like a more accurate reflection of what I'm looking at. Boy, I wish I'd had that a few days ago! Just ordered the PWM chip, thanks Dick.

[R_J]

Re: Dead Vestel 17IPS71 power board

That 17ips71-r3 schematic with R294 is drawn WRONG. R294 cannot be connected that way, if it was the ic would get aprox 390vdc on the VDD pin and the ic would get blown off the board.
The 17ips71-r4 schematic in post 149 would be correct.

[budm]

Re: Dead Vestel 17IPS71 power board

Yep, that schematic, 17ips71-r3, from post #17 is not from Vestel, it looks like it was drawn by some one else with lots of wrong value parts, I.E. lots of resistors are marked as '10R', and connections.

[FullnameJon]

Re: Dead Vestel 17IPS71 power board

I've gone through this thread a couple of times but my issue doesn't seem to match, I think. I get 12 and 24V outputs, but not stable. I can hear something restarting every couple of seconds and the voltages on the DC side drop just a little bit before it goes up again, and then down a bit. No standby light and no life in the TV other than the unstable voltages. I've replaced FAN6300A as I thought that was causing the issue, but no luck. Bad caps? Bad IC?

[dick_barton]

Re: Dead Vestel 17IPS71 power board

What version is your board r2, r3 etc???

What voltage do you have on the pins 1 - 8. Use the negative leg of C19 as the ground for your meter. Be carefull since there is high voltage on this part of the circuit so measure with a steady hand.

What voltage do you have between the two pins of C19. Should be close to 400V and steady

[FullnameJon]

Re: Dead Vestel 17IPS71 power board

Board is R4.

Pins 1-8 where?

C19 is 320-321V

[dick_barton]

Re: Dead Vestel 17IPS71 power board

FAN6300A was what I meant but ignore for now.

Can you post a photo of your board.

Can you also give the voltages you have on each of the pins of connector CN3 or CN4 whichever one is fitted to your board.

[FullnameJon]

Re: Dead Vestel 17IPS71 power board

1 - 24V
4 - 2.5V
10, 11, 12 - 12V

Again, it moves around a bit as the supply restarts.

[dick_barton]

Re: Dead Vestel 17IPS71 power board

It looks like the diodes have had their legs cut to check them but D13 and D15 look as though they are not soldered back in place correctly.

You have missed some of the voltages on the connector

[FullnameJon]

Re: Dead Vestel 17IPS71 power board

I noticed that too but they're connected. Didn't bother tidying it up yet.

Pin 9 shows 1.5V. Where does that come from? There's no Q1.

[dick_barton]

Re: Dead Vestel 17IPS71 power board

Disconnect the mainboard from the power supply and power up. Check if Pin 9 of CN4 = 5V. If not then this voltage comes from the mainboard and is fed back to the power supply.