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

[Dannyx]

Good day folks. I thought I'd share with you how I repaired a Vestel 17IPS20 power supply in a Toshiba TV and hopefully this will help others who might be facing this issue as well. The TV appeared totally dead, that is, not even the LED at the front came on. With this being Vestel, I was expecting either a fried primary or a shorted rectifier diode, like it usually happens, but upon taking the board off and probing around, I got neither of these: no shorts and the fuse was also OK, so power was definitely going into this board. Taking a closer look, you can see the area around the FET in the top left of the board (well, RIGHT if you look at the picture that I took) looks a bit charred, although surprisingly the FET and all the components around it were OK, so I didn't bother to replace them for the time being. Flipped the board over and continued my searches on the bottom of the board: the first thing I checked was to see if power was going to the switching ICs. There's 3 of them: 1 for PFC, 1 for the main low voltages (12 and 5v) and one for the LED driver which is what the FET located in that darkened area of the board is for. Measuring the VCC pins of these showed some intermittent voltage, though too low for sustained operation (I think I got like 3-6v) so there seemed to be a short somewhere. The VCC for the 3 ICs is supplied by the same AUX winding of the transformer (the one in the middle) and I was lucky that the IC running the LED FET was connected via a jumper wire to this winding. This allowed me to pull out one end of the jumper to see which of the 2 ICs was pulling down the AUX winding. Sure enough, with the jumper out and no power going to the LED driver (U300), the AUX winding went up to 9v and I also got the correct 12v on the output of the supply, since the main switching IC was still connected and operates without a PS_ON signal - it's always on. This told me I needed to focus on the driver for the LEDs. Putting my meter probes across GND and VCC of U300 immediately revealed a short. Given the heat that area was subjected to, I wasn't sure whether the fault lay in the IC itself or the capacitor C397 placed between VCC and GND, so of course I took the easier approach first and pulled out the cap rather than the whole IC. This solved the issue: the short was no more and the cap was indeed shorted. Looking at the schematic, C397 is a 1uF cap. Not having a SMD one on hand, I took a regular electrolytic and botched it between a ground trace and the VCC pin of U300 just to see if it would indeed fire all the way up - it did. The TV is back in business So the next time you're faced with a Vestel PSU that doesn't seem to have any immediate faults, check the switching ICs - it might be something really simple to solve.

[dskall]

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

Nice job Dannyx. Thanks for sharing troubleshooting and repair.

[budm]

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

Good find.
There are many (at least 5 that I see in the diagram) MLCC on that VCC line, you are lucky to find just the right one
Is the Q216 (schematic page 2) switched Transistor that supplies the switched VCC to run U300 and other ICs Ok?

[Dannyx]

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

Good find.
There are many (at least 5 that I see in the diagram) MLCC on that VCC line, you are lucky to find just the right one
Is the Q216 (schematic page 2) switched Transistor that supplies the switched VCC to run U300 and other ICs Ok?

Yes it's OK, otherwise the set wouldn't have worked, right ? However I DID check it so I know it's fine, in case you were suggesting that perhaps it became shorted and now the ICs remained on all the time, even when the PS_ON signal is not present. Also, CORRECTION: in my initial post I wrote that there's no PS_ON signal, but it appears there actually is one now that I look closely at the schematic. That's one thing about Vestel boards which I've noted: the schematics show every part that can go on that particular model of board, even though the actual board may have some entire circuits missing.

[budm]

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

If that transistor is shorted out then the VCC will be present all the time instead of being turned on, or OFF. So all you have to do is to see if VCC is present all the time or not.

[cat02]

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

thanks for that. i had a dead pp 17ips20 and there were no shorts or leakages on the o/p diodes. it was a 42!! walker. the fuse was ok and i had the vcc voltage going to the 3 chips in primary of pp..luckily i had a spare good panel to make comparisons and evetually i found a leakage on octocoupler u201 at top of board. there was also a bit of green mould around this opto which prob caused the fault, possibly a drop of water or beer, as it was from the local racecourse...cleaning this and fitting an octocoupler got tv fixed

[Dang]

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

Hi, been a while since I've been here but just wanted to confirm that I had the exact same issue as the OP (thanks to the OP for clear info), so it seems to be another common fault with this power supply. I've now fixed the power supply as described and all is working OK (touch wood), just another thing to look out for if your having problems, thanks.

[Dannyx]

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

Hi, been a while since I've been here but just wanted to confirm that I had the exact same issue as the OP (thanks to the OP for clear info), so it seems to be another common fault with this power supply. I've now fixed the power supply as described and all is working OK (touch wood), just another thing to look out for if your having problems, thanks.

Glad I could provide some useful info Cheers.

[pete_the_geek]

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

Excellent tip there Dannyx, was beginning to suspect the TL431 (U203) as it seemed the 12V rail overshot while the PSU was pulsing.
How ever read your thread went straight to my faulty IPS20-R6 and measured C397 on diode test...32R! Replaced and set sprung into life.

Nice work, thanks

[darkdead]

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

Add on fault when the V led is like ok but the led brightness is low nothing (on but like at 3%) the Q501 to q501 (there are some revision whit 1 to 4 mosfets) are short.
it triger the overload protection on u500 (mp3334) and no PWM signals on the gates of mosfets q502 q50e.
My tv got 120v the 24-80v line and after q502 -503(some got 1 other boards 2) 150v .
When low brightness 24-80v the voltage on V led is the same when the circuit is step up DC to DC whit current control(150v).
The tv was a vestel philips.

[HellasTechn1]

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

I have the same problem as described in post No1 but when i measured the VCC voltage on U300 (6300A), U202 (6300A) and U101 (FAN 7529) the multimeter showed 0V.

Ive checked their capacitors c397, c295, c296 and c127 and appear to be okay.

Also i have checked all semiconductors (mosfets and diodes) topside of the board and appear to be okay.
I have no idea what else to check.

Please note that all measurements (appart from Voltage) where taken witn a Huntron Tracker 2000. Pretty old i know but handy with diodes and transistors. Capacitors are tricky to troubleshoot with it but at least i can tell if completely shorted or not.

Thank you all in advance !

[Dannyx]

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

Try to trace back the AUX winding where that VCC AUX is supposed to come from and measure from there.

[HellasTechn1]

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

when i measured the VCC voltage on U300 (6300A), U202 (6300A) and U101 (FAN 7529) the multimeter showed 0V.

I may have measured between the wrong pins. For U202 and U101 i measured between pins 4 and 6. Also the mainboard was disconnected...

Which are the aux windings pins ?

Please forgive me that i am really inexperienced and with little knowledge on electronics.

Thankyou.

[Dannyx]

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

Let's see if we can go over this, since it's been such a long time and can't remember it well. To make your life easier, when measuring "primary" "hot" components, you can grab your ground (negative probe) from the - leg of the bridge rectifier - it's nice and remote so you don't risk accidentally touching your probes and making a nice bang. So ground your probe on the bridge rectifier and now have a look at the schematic: attached to pin 13 of TR200 (use the search function to locate this) there's D214 which takes the VCC Auxiliary voltage and rectifies it, which is then used to power those three ICs I mentioned. Measure its cathode (output) and see if you get anything. If you don't, trace back even further: do you have voltage on the main capacitors ? Is this board getting any power at all ? Silly question: fuse ? Check the large gray resistors for the sources of the FETs - they should have low values and "conduct" (your meter should beep in continuity mode), though those seldom fail, unless the supply has experienced a particularly large spike on the mains and the FETs are toast....

[HellasTechn1]

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

Awesome. Now how dumb can i be ?

I measured the cathode of d214 and got an unstable voltage from 2,5 to 3 volts. I wanted to use the Oscope to take a picture of it and i forgot that the negative probe of the Oscope is earthed...
Now i have a blown fuse and 2 shorted diodes Fixing it and reporting back.

[Dannyx]

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

Well at least you have a scope as opposed to me ! Yes, the ground probe of the scope goes to earth, so you can't measure stuff on the live side without an isolation transformer or by simply lifting its ground pin from the outlet, otherwise something goes boom.

[HellasTechn1]

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

I am sorry to hear that brother. Everyone should have such tools.
I was lucky enough to have one from my father.

Okay i restored the diodes and fuse and now i am getting an unstable 5 to 5.3 volts from the D214...

Funny thing is that when i used my old analog multimeter it reads 0 volts at the cathode of d214... I am confused. Why would the DMM show reading while the AMM nothig ? (i have confirmed it can measure DC from an other psu.)

Ho and by the main filter cap reads 315 Vdc

I am calling it a "night"... See you tomorrow !

[Dannyx]

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

Could be a short like I had, since what you describe is pretty similar...probe that same point in continuity mode and see if you get low resistance between it and hot ground. If you do, something's pulling that AUX output down...that would be my only explanation so far :|

[HellasTechn1]

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

Could be a short like I had, since what you describe is pretty similar...probe that same point in continuity mode and see if you get low resistance between it and hot ground. If you do, something's pulling that AUX output down...that would be my only explanation so far :|

I will. Also i assume the aux winding of the transformet is powered on all the time to provide stby voltage. Yes ? In other words it does ot require the mainboard to me presint.

Still why the analog meter reads nothing ? It is not dead that i can tell.

[HellasTechn1]

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

The anode of 214 is connected directly to the aux winding yes ? so from the anode to the ground i measure 1 Ohm (shorted) and from the cathode of the diode to the ground i measure 5 Mohm.

Again that is normal i think since the other end of the winding is connected to GND. i am only measureing the windings resistance...