Bad Vestel 17IPS20 : shortage, need help

[worlor]

Hello,
My Vestel television has stopped working.
After first diagnosys, the power board 17IPS20 R6 don't work (no 12V on output).
I have replaced :

• U300 FAN6300 -> completely blown up
• Q301 MOSFET FQPF8N60C
• C387 1uF Capacitor -> shorted
• C295 & C296 1uF capacitor -> to be sure

But with my multimeter, there is conductivity between VCC and GND on U300 and U202. I don't know why. Maybe a diode but i can't test these because of the short.
Can you help me to find the cause of the shortage ? have you any ideas ?

I attach schema of the board + pictures

Thanks for help

[dick_barton]

Re: Bad Vestel 17IPS20 : shortage, need help

U300 shows 2 x 10 ohms resistors to ground from VCC so that could be the reason why VCC to ground measures low. What reading do you have?

[budm]

Re: Bad Vestel 17IPS20 : shortage, need help

Hello,
My Vestel television has stopped working.
After first diagnosys, the power board 17IPS20 R6 don't work (no 12V on output).
I have replaced :

• U300 FAN6300 -> completely blown up
• Q301 MOSFET FQPF8N60C
• C387 1uF Capacitor -> shorted
• C295 & C296 1uF capacitor -> to be sure

But with my multimeter, there is conductivity between VCC and GND on U300 and U202. I don't know why. Maybe a diode but i can't test these because of the short.
Can you help me to find the cause of the shortage ? have you any ideas ?

I attach schema of the board + pictures

Thanks for help

Best to tell us what the exact resistance reading is.

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

U300 shows 2 x 10 ohms resistors to ground from VCC so that could be the reason why VCC to ground measures low. What reading do you have?

Best to tell us what the exact resistance reading is.

Hello,

I have measured 28 Ohm between VDD and GND on U202 and 26.5 ohm between VDD and GND on U300.

But I have measured also R558 and R559 at 100kohm each and it's written 104 on it. I don't understand why it's not 10 ohm like in the schema

[dick_barton]

Re: Bad Vestel 17IPS20 : shortage, need help

Can you check D214, D215 and Q216

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

Sure, the mesure shows that diodes are passing in both way but is this behavior can be caused by the short ?

Thanks for help

[dick_barton]

Re: Bad Vestel 17IPS20 : shortage, need help

Emitter / collector appears to be short circuited. You would need to lift the transistor to confirm there is no short circuit across the emitter /collector circuit pads.

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

Ok after desolding and test, it seems the transistor is OK
see pictures

[budm]

Re: Bad Vestel 17IPS20 : shortage, need help

Hello,

I have measured 28 Ohm between VDD and GND on U202 and 26.5 ohm between VDD and GND on U300.

But I have measured also R558 and R559 at 100kohm each and it's written 104 on it. I don't understand why it's not 10 ohm like in the schema

The component values in the schematic are not the actual values used for your PCBA (PCB Assembly), that schematic is the Master schematic for creating blank PCB, then the PCB will be stuffed with the correct component values as needed to make PCBA, you can also see that not ALL component are installed on your PCBA.

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

The component values in the schematic are not the actual values used for your PCBA (PCB Assembly), that schematic is the Master schematic for creating blank PCB, then the PCB will be stuffed with the correct component values as needed to make PCBA, you can also see that not ALL component are installed on your PCBA.

Ah okay, thanks for the explanations !

Do you have any clues on why my card don't work ?

[budm]

Re: Bad Vestel 17IPS20 : shortage, need help

Ah okay, thanks for the explanations !

Do you have any clues on why my card don't work ?

I need to look at the pictures of your board and the schematic first before I can give you the test points to test.
Also look at the results of your post #8 again.

[cheeky2]

Re: Bad Vestel 17IPS20 : shortage, need help

Ok after desolding and test, it seems the transistor is OK
see pictures

Since when should a transistor have a short circuit between the emitter and collector??? I don't understand how you could think its ok!
I would suggest you read up on how to test transistors as your diagnosis is floored with regards to the transistor.

[dick_barton]

Re: Bad Vestel 17IPS20 : shortage, need help

Ok after desolding and test, it seems the transistor is OK
see pictures

Emitter / Collector is short circuited.

[R_J]

Re: Bad Vestel 17IPS20 : shortage, need help

If Q301 was shorted, it should have opened R320 (which is usually a low ohm resistor) if R320 did open, it supplied full PFC voltage to U300 via R311 (likely open now as well) which blew up u300. If the shorted transistor is Q216, this would have shorted due to a short on the VCC line, so U202 could also be bad.

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

Thanks for help, I have ordered a new BC327 for replacement.
I have re-checked D214 and D215 whitout the transistor and they are OK (OL in blocking, 0.5V in passing for D214, 0.6V for D215)

If Q301 was shorted, it should have opened R320 (which is usually a low ohm resistor) if R320 did open, it supplied full PFC voltage to U300 via R311 (likely open now as well) which blew up u300. If the shorted transistor is Q216, this would have shorted due to a short on the VCC line, so U202 could also be bad.

Is there a way to check U202 is good ?

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

I have checked R320, it's a 0.47ohm 2W resistor.
He was not open, but a chunk of ceramic was missing on it
The multimeter show 82kohm.
I have ordered a new one

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

For R311, i measured 48 Mohm, I think it's dead too.
But I can't see the value on it :/
It seems it's a 470 ohm, do you think it's correct ?

[R_J]

Re: Bad Vestel 17IPS20 : shortage, need help

R311 seems to show 471 (470Ω) If R320 has a chunk missing it is likely open and if there are any diodes across it (D512,D513) they are likely shorted.

[worlor]

Re: Bad Vestel 17IPS20 : shortage, need help

R311 seems to show 471 (470Ω) If R320 has a chunk missing it is likely open and if there are any diodes across it (D512,D513) they are likely shorted.

No, R320 is damaged but it's not open. I measured 82kohm on it : it's far from 0.47ohm
I will replace

[arizanotlari]

Re: Bad Vestel 17IPS20 : shortage, need help

17IPS20 Power Board Presentation : https://yadi.sk/i/FUHv-yP4doTRvw