Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Okay. I used 2 pole cable no earth to the Oscope. I measured the cathode of d214 and gives me noting at all. then i measure the cathode of D215 and gives me a nice 13.7V. like in the picture.
That is strange... If the secondary winding feeds the first diode and then in turn the diode feeds the second diode then why i get no voltage from the winding while i get 13.7 from the second diode ?

Please note that the PSU is not connected with the mainboard.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

If you do have 13.5v on VCC_MAIN (VCC_M) You should have the other voltages from the transformer (24v_AC) which feed diodes to give 24volts on C213/217 and (12V_AC) which feeds D210 to give 12V_DC which goes through L200 to give +12VCC which gives +5V_STBY through Q212 (transistor acting as +5v regulator)

Yes i do have 13.7V VCC_MAIN BUT I have nothing on C217 or before the diodes feeding it (actually i do have 118mV).

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

U101 as well as U300 have no VCC... I have to scope TR200 to see what comes in and goes out, right ?

Could you help me understand the pinout of the actual transformer ?

Also i am reading almost short on D111 but again it might be due to that resistor r130 connected in parallel. I think its a 10 Ohm

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

U202 FAN6300 has an internal startup cell: when power is first applied to the board, there would be no VCC_MAIN present because U202 has no VCC to switch TR200 to generate anything, so the IC takes some current from its HV pin (which is at HOT+) and feeds it THROUGH the IC into the VCC pin to provide its own startup until VCC_MAIN takes over. The VCC pin is connected to D215 and it also explains why you get something after D215 but not before: it comes from the VCC pin itself. It also explains the role of D214 - blocks VCC from U202 from going back into the transformer. It looks like U202 is not switching. Probe its 5th pin (GATE_M in the schematic) and see if you get any switching action from U202, provided it has VCC on its pin coming through itself.

[R_J]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Good catch dannyx, that must be the reason, On a normal schematic drawing it may have been more obvious, at least they put the transformer and the ic and fet on the same page.

If there is no gate pulse check that D298 or Q215 is'nt shorted, 13.5 volts vdd is above the 10 volt turn off so it should be turning on if its ok.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

U202 FAN6300 has an internal startup cell: when power is first applied to the board, there would be no VCC_MAIN present because U202 has no VCC to switch TR200 to generate anything, so the IC takes some current from its HV pin (which is at HOT+) and feeds it THROUGH the IC into the VCC pin to provide its own startup until VCC_MAIN takes over. The VCC pin is connected to D215 and it also explains why you get something after D215 but not before: it comes from the VCC pin itself. It also explains the role of D214 - blocks VCC from U202 from going back into the transformer. It looks like U202 is not switching. Probe its 5th pin (GATE_M in the schematic) and see if you get any switching action from U202, provided it has VCC on its pin coming through itself.

I had no idea :P I could never imagine that. Thank you ! ill keep you posted.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

YOU HAVE A SCOPE ! USE IT ! Off-topic - what scope have you got ?

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

If there is no gate pulse check that D298 or Q215 is'nt shorted, 13.5 volts vdd is above the 10 volt turn off so it should be turning on if its ok.

There is no gate pulse, nothing. And yes D298 is fine while Q215 is not present on my board.

I think it is normal not to have gate pulse if the transformer is giving out nothig. shouldn't i investigate what is going on on the primary of the transformer ? Could you please help me identify the transformer pins o the board with their corresponding numbers on the diagram ?

YOU HAVE A SCOPE ! USE IT ! Off-topic - what scope have you got ?

Its a tek dts3012.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

There should be a gate pulse thanks to that startup cell I mentioned. U202 powers itself briefly for just that very reason - to continue pulsing that gate to allow the transformer to generate something. I'd replace U202.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Since i dont have a spare FAN6300, i can just swap U202 with U300 and see if i get pulses on pin 5 and stby voltages in general. Right ?

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

If they're the same, yeah, it should work, but check the ICs themselves first to ensure they really are identical, otherwise you could have a bang, despite what the schematic calls them

[gabiz_ro]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

In first photo,top right,there is one mosfet.
Heatsink is too little,you can see almost burned PCB.
Encountered in few cases Q301 (if I remember right code) shorted G-S as result no backlight.
Also can see footprint for bigger heatsink.
I replaced original with another (big one) heatsink and Q301 from very hot now was little warm,so I reccomend to add a bigger heatsink to Q301.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

I removed the old U202 and replaced it with U300 leaving U300 unpopulated and clean from solder residue.
Now i have the pulses on pin5 of u202 and also i have ac voltage from the transformers aux winding.
I am going to put the psu on the TV to see what happens. I expect it to power on but without backlight because from what i understand so far U300 is feding tr301 that provides 24V for the LED driver. Am i wrong ?

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

In first photo,top right,there is one mosfet.
Heatsink is too little,you can see almost burned PCB.
Encountered in few cases Q301 (if I remember right code) shorted G-S as result no backlight.
Also can see footprint for bigger heatsink.
I replaced original with another (big one) heatsink and Q301 from very hot now was little warm,so I reccomend to add a bigger heatsink to Q301.

Not a bad idea as long as the heatsinh is of low profile and will fit with the back cover installed.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

The back of these Vestels is quite fat if I remember correctly, so it should fit no problem. Don't even bother soldering the "dead" IC back on the board - just try it out without it, see if you get startup and then install the missing IC for the backlight driver.

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Hmm. I now have 26v on d208, 12V on d209 d210 and d211, I get 12 and 24V on the mainboard. Still the TV will not turn on. No stby light nothing in general.
I do not see the 5V anywhere... Im going to check q212 but so far i have been unable to locate it on the PCB.
Does anyone know where is it located ?

Any ideas in general ?

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

Great, q212 is not installed on my board. How can i locate the source of 5V ?

It may sound silly but is it possible that 5V come from the led driver circuitry ?

I also noticed that the connector diagram is not the same since pin 9 on the diagram is supposed to supply the 5v_stby but in fact it is not connected anywhere since q212 is not installed and so the jumper to it is also not installed.

[Dannyx]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

It's possible the main board just uses 12v as standby and has no 5v output directly (the way mine did)...do you get any voltage going into the main board anywhere ? Could be a bad MB as well. Might want to search for a schematic for that board to see how power is routed around it (possibly a 17MB82s, though I may be wrong).

[HellasTechn1]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

I can confirm the 12V and 24V going to the mainboard but other than that i dont know.

Mainboard is VESTEL 17MB95M

[vinceroger69]

Re: Dead Vestel 17IPS20 power supply repair (OK fuse, no shorts)

this maybe the mainboard service manual