No Voltage on POK pin Philips 42pfl6007h/12

[Gjackson]

Hi, my tv works fine apart from the backlight which I found was due to a couple of blown Fet's that I haven't yet replaced however I have no 5v on my POK pin, is this normal? I found a schematic for my power supply and it seems that IC701 generates the voltage on it's VREF pin, after measuring this pin it seems to be working fine as I see a steady 5vdc output, the reason that this voltage is not getting delivered to the pin is due to a 7.5kohm resistor between the IC and the pin. (schematic below) any ideas as to what's going on? maybe my tv's motherboard doesn't require a POK signal? Thanks

[dick_barton]

Re: No Voltage on POK pin Philips 42pfl6007h/12

If you still have the blown fets then the backlights will not be working (as you say) so there may well be no UC1' to supply ZD702.
I would check again when the mosfets have been replaced.

[Gjackson]

Re: No Voltage on POK pin Philips 42pfl6007h/12

Thanks for the reply, to be more clear the dead Fet's are Q701A and Q701B. I'll read POK again when I replace them, Could you clarify what UC1 and UC2 do?

[dick_barton]

Re: No Voltage on POK pin Philips 42pfl6007h/12

Whar values are R719 and R720
What resistor number on the circuit are you refering to as the 7.5K resistor
If Q702 is not installed then you should have some votage at POK. There's a resistive divider R719 and R720 reducing the Vref voltage down to provide the POK voltage

[Gjackson]

Re: No Voltage on POK pin Philips 42pfl6007h/12

Hi I've replaced those two backlight mosfets that I had removed and I now get a 3.3v voltage on the POK pin, this makes sense to me as this tv has a logic signal of 3.3v thank you for your help!

[dick_barton]

Re: No Voltage on POK pin Philips 42pfl6007h/12

Is your set up and running now?