Philips 42PFL5432D/37 power supply issue no 12v

[Ifixstuff9]

I have a Philips TV that shows no signs of life when plugged in - no standby LED, no response to buttons, no noises, nothing. This model is well known for having bad caps, so I started by replacing a few of them (3x 35v 1500uf and 1x 2200uf 16v). I don't know the history of the TV but it looks like someone's been at it before because some of the solder joints looked really bad, so I re soldered them as well.

After swapping the caps I still got no signs of life so I started checking voltages, and found that the board is supplying 24v but not 12v. Here's what I measured on the connector to the main board:

Pin 1 +24v --------------- 24v
Pin 2 +24v --------------- 24v
Pin 3 +12v --------------- 490mv
Pin 4 +12v --------------- 490mv
Pin 5 Brightness Adj ----- 0v
Pin 6 Inverter ON/OFF --- 0v
Pin 7 GND ---------------- GND
Pin 8 GND ---------------- GND
Pin 9 GND ---------------- GND
Pin 10 Stand By ---------- 0v
Pin 11 GND --------------- GND

Any thoughts on why I have 24v but not 12v?
Also I was able to find the service manual for this TV here:

[R_J]

Re: Philips 42PFL5432D/37 power supply issue no 12v

IC907 is the drive ic for the 12 volts, Start by checking if it has VCC on pin 1 (You must use hot ground for your negative meter lead) and check if it has Drain voltage on both sides of R951.
Or you can start by checking R974, R976 and Q906

[Ifixstuff9]

Re: Philips 42PFL5432D/37 power supply issue no 12v

I checked IC907 and got 1.53v on pin 1, and 160v on both sides R951

[R_J]

Re: Philips 42PFL5432D/37 power supply issue no 12v

I checked IC907 and got 1.53v on pin 1, and 160v on both sides R951

So the VCC is way too low, this could be due to a shorted ZD908, or the ic could be bad, The ic has a startup cell so make sure C957 is ok and not open. Then Check R974 to make sure it is not open.

[Ifixstuff9]

Re: Philips 42PFL5432D/37 power supply issue no 12v

I tested ZD908 in circuit and it's not shorted. Checked C957 and it's not open, neither is R974

[R_J]

Re: Philips 42PFL5432D/37 power supply issue no 12v

It's likely IC907 that is bad, you have 160vdc on R951 which supplies the ic pin8, internally the ic will produce a startup vcc of approximately 4vdc, If the ic starts and gives a pulse to Q908, it will drive the transformer primary and the feedback winding and D908 will charge C957 to about 11vdc. and then the ic will start operating.
You could check that nothing on the secondary side is shorted, such as D927

[Maalobs]

Re: Philips 42PFL5432D/37 power supply issue no 12v

See here about downloading the service manual.