Dead Vestel 17IPS20 - MOSFET short circuited

[Askic]

Hello guys,

yesterday, I have killed 17IPS20 23117579-27002042, by accidentally making short circuit on MOSFET Q211m while trying to measure coltage on its legs. According to the schematics I could find in the Internet Q211 is FQPF8N60C. Please have a look at the attached picture. I have short circuited Gate and Source. After this I don't even have StdBy voltages on the connector.

What else could be potentially damaged so I can check before ordering replacement parts? I ask this because I couldn't find exact schematics for this particular revision. I believe it is revision 5 because there is a number on the PCB: 040313R5.

[nomoresonys]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Why do you have two threads about the same tv?? we can plainly see the first thread, these double threads are frowned upon and they only shit up the boards and you still haven't posted ALL the pictures asked for in the first thread if you can't follow simple directions then HOW can anyone help you??

[Askic]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Why do you have two threads about the same tv?? we can plainly see the first thread, these double threads are frowned upon and they only shit up the boards and you still haven't posted ALL the pictures asked for in the first thread if you can't follow simple directions then HOW can anyone help you??

Because the original problem is solved by replacing the board with another one.
Here, I want to try to save this board and keep it as spare.

I didn't post pictures of the broken TV in this thread, because I took its supply board (17IPS20 different version), MB (17MB82s) and LED chassis and installed in the other TV. So, there was no point to troubleshoot that further, because I assumed T-con was bad and I was right.

I started another thread, because it's a different type of a problem on a different TV.

[nomoresonys]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Alright then, looks like you're in the clear, lol, well maybe it will keep someone else from double threading.

[petehall347]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

i believe its good practice to check gate drive resistors to save fets blowing again .

[R_J]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

There is a source resistor next to the mosfet (R228?) it should be a low value 0.33~0.47Ω.
If the mosfet shorted, it might have also opened that resistor. If it is open, check R242 and if it is open the ic is likely bad as well.

[Askic]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

There is a source resistor next to the mosfet (R228?) it should be a low value 0.33~0.47Ω.
If the mosfet shorted, it might have also opened that resistor. If it is open, check R242 and if it is open the ic is likely bad as well.

Yes, there is a resistor R228 that should be 0.47Ω. This resistor is now open.
There is also R242 (image nr 2), but it is steady 2.56 kΩ, so I'm not sure what to think of it.

I have noticed also that two diodes D512 and D513 that are next to Q301 MOSFET are conducting in both directions (when multimeter is switched to diode checking. One direction of instrument leads displays 585 and other 595). The both diodes have the same behavior.

It seems I don't have right 17ips20schematics because for R228 on this schematic is written 120R and in fact on the body of the resistor it can be read 0.47Ω. The same goes for R242

[petehall347]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

D512 and D513 that are next to Q301 MOSFET are conducting in both directions
i guess you are checking in circuit ? if so lift one side of one or both and test again .

[yokoono]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

You will not repair the power supply if you do not replace the pwm U202 controller (apart from all other related components).

[Askic]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Yokoono, can you please help a bit more. It is very hard to read what is written on U202. It seems to me: TD 1AD 6742HR SYD. Is that so? On the schematic I use there is no U202 under that number. There is SG6742HR. I believe I don't have appropriate schematics. Is that part TD1 AD important?
Thank you.

[nomoresonys]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

It also won't work if one of those diodes is bad so lift a leg and check it out of circuit.

[dick_barton]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

In post #7, R217 just below U202 looks damaged?

U202 is an SG6742HR device

[R_J]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Yes, there is a resistor R228 that should be 0.47Ω. This resistor is now open.
There is also R242 (image nr 2), but it is steady 2.56 kΩ, so I'm not sure what to think of it.

I have noticed also that two diodes D512 and D513 that are next to Q301 MOSFET are conducting in both directions (when multimeter is switched to diode checking. One direction of instrument leads displays 585 and other 595). The both diodes have the same behavior.

It seems I don't have right 17ips20schematics because for R228 on this schematic is written 120R and in fact on the body of the resistor it can be read 0.47Ω. The same goes for R242

Yes the schematic is wrong for R228, the correct value is 0.47Ω in your case.
R242 should be 10Ω (marked 100)
When R228 goes open and the fet is shorted, aprox 300v is applied to R242 and the ic, you see what it did to R242, imagine how the ic handle it inside. The ic is damaged for sure. Also check R217 gate resistor, it might be damage also.
D512 & D513 are likely ok and have a resistor (R320) across them, which is likley a low value. (what is the value of R320?)

[Askic]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

R217 shows about 33 kΩ, but this value slowly drifting up (like some condenser is charging), so it's dead also.

Value od R320 should be 0.33Ω (it's written on it) and when measuring, the instrument shows steady 0.6 Ω, so it's probably good. The diodes are good, I have check them by lifting legs out.

Ok, thank you guys, I'll see what are the delivery times when ordering from ebay and then decide what's next.

[R_J]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

When measuring low ohm resistors, you need to take into consideration the meter lead resistance, short the leads together, what is the resistance? It could be 0.27Ω.
Lead resistance + resistor value = displayed value

[Askic]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

Hello RJ, yes I have checked that. When leads are shorted, the instruments displays sometimes 0.1 and sometimes 0.2. That is why I wrote that R320 is most probably OK.

I really wonder what is the correct value of R217, according to the schematic it is also 10Ω.

[R_J]

Re: Dead Vestel 17IPS20 - MOSFET short circuited

What is marked on the resistor? 100 = 10Ω; 101 = 100Ω, The datasheet for the ic lists a 100Ω