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

[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

[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)

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)

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)

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)

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.

[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.

[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.

[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

[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)

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.

[Dannyx]

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

Given what RJ said, yes, you measure VCC MAIN with chassis ground reference, since it's secondary (after a diode that should be there to rectify it, of course). Yes, lift the scope from ground - simplest way that I can think of to do that is to use an outlet without the earth connected or with no earth entirely...just for testing purposes. Correct me if I'm wrong - I did this myself when I had ground loop issues with an external sound card and my laptop: I plugged the laptop's power brick into a splitter with no earth and it was solved

[HellasTechn1]

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

Allright. Now before i go ahead and use the Oscope shouldn't i first disconnect the GND wire on the mains power plug ? i dont want to short anything again like last time...

Also to read the 13.5V i use ground reference right ?

[Dannyx]

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

Yeah, it's been a while since I've tinkered with a Vestel.....I need to brush up on my SMPSs

[R_J]

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

No, If the ic is NOT working you will NOT get VCC_MAIN. although it is drawn on the primary side it is a scondary winding, so no primary switching, no secondary voltage.

[Dannyx]

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)

....provided the IC itself is operational, which it most likely is in this case, since those rarely fail without some damage on the primary first.

Still, if you DO get VCC_MAIN and nothing out the output, perhaps the IC is dead and not switching...scope to the rescue: probe its output pin that drives the transistor. Man, wish I had a scope right now

[R_J]

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

I missed that in the picture, should have looked closer. thanks dick_barton

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)

[dick_barton]

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

Can you confirm that VCC_Main as shown in post #23 is steady at 13.5V

[Dannyx]

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

Good spot...I couldn't tell the difference between U202 and U300...I think U300 is for the LED driver and it's "switched" (just like U101 for PFC) whereas U202 runs all the time to generate standby...damn

So yeah, with that being said you STILL need to check if the AUX winding outputs anything to power U202, then if it does see if you get standby, then if you don't trace everything back from there....such a pain in the butt...I much prefer a supply that's completely blown apart, at least you know what to replace at a glance

[R_J]

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

Your board is a 17IPS20 060913R6, so that should be the schematic. These are a real POS to follow.
The circuit that needs to be working is the one for U202/TR200, it supplies 12V_AC to get 12v_DC which supplies +12VCC_S which supplies Q212 and gives +5V_STBY
TR200 also supplies VCC_MAIN, Q216 is a switch that controls VCC that supplies U300 etc. Q216 is basically controled by ST_BY from the main baord.
So you need st_by ON signal from the main board to have VCC on U300