Philips 40PFL3505D/F7 Question about FET replacment

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Measure voltage across C1607.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

There is 117V DC

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Seems very low. What is your AC line voltage?

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

120VAC. Did you see the last post on page 1, Im getting 345V on center pin of Q1701, but nothing on other legs.

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

I suspect IC1702 TEA1611T.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Pins 8 SH, 9 GH, and 10 VDD, are those voltages coming OUT? Because I have about 0v on all 3 of those pins. On the other side I DO have the voltages, like VAUX, VDD, RESET, and GL.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Hey Tom I ordered the new IC, but out of curiousity based on the pic are pins 8-10 the outputs from the IC? Im just not sure if that is voltage going into or out of the IC.. Thanks!

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Outputs are pin 9 and pin 12. Pin 8 is midpoint sense (used to drive pin 9 gate FET so it is not damaged.)

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

OK so Im getting output 6V from GL but nothing from GH, does that tell you anything?

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

And pin 8 you get?

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

When I checked I was getting little to nothing from pins 8-10. Nothing even close to 170V. I have the working PS board and those voltages were all high, and the ones on the right side were all the same. I just wasnt sure if one of those 170v was supposed to be coming into the IC and maybe that was missing. If that makes any sense...

Another words where is this 170+-V coming from?

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

The only way that could happen is the IC switches on the lower FET but then doesn't turn the next stage on (the upper stage.) I think it is faulty because if it were disabled then both channels should be at near zero, it makes no sense to keep the lower FET switched on all the time.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Thats what Im asking so that 174V at the gate of Q1701 should be generated by the IC?

[tom66]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Yes. The chip generates about 10V~15V between pin 8 and pin 9. This turns the FET on. Note that when first starting, the mid point voltage on pin 8 will be low (0V). It will slowly ramp up to half the supply voltage, around 160V or so. The voltage on pin 9 will follow it. But it looks here like the chip just has the low output continuously enabled for some reason, I'm not sure why.

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Ok thank you will let you know after new chip arrives..

[kevinm34232]

Re: Philips 40PFL3505D/F7 Question about FET replacment

Hey Tom received and replaced IC1702 and that fixed backlight and finally fixed this power supply, thanks for the help!

As a side note, these boards are really sensitive and the pads easily will come off the board with any pressure and heat.