Phillips 32pfl3504d/f7

[HairyManBack]

I recently got my hands on this tv to fix for a friend. When i first opened it up i saw that the fuse was blown and i saw a zener diode had split in half. The zener is a 27 volt half watt, its d606 on the schematic. I decided to check all the diodes in that area and replaced one switching diode i think it was d609, it showed that it was open on my ohmmeter. I took out the n channel fet k3563 which is q601 on the schematic and it was open also so i replaced it. I also checked all of the diodes in the bridge rectifier and they were all good, they read ol in reverse polarity and a small resistance (which i cant remember) in forward polarity. So i put everything back in, put in the new fuse, and components and plugged it up and it blew the fuse. Any suggestions would be great.
Here is a link to the schematic...


the site is Spanish but the manual is not. lol

[Phaihn]

Re: Phillips 32pfl3504d/f7

[Phaihn]

Re: Phillips 32pfl3504d/f7

oh and post some good clear pictures take the picturs by a window if you can.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

I will try to find my camera... lol. I took the diodes in the bridge rectifier to check them out and they are good. I took the cap from c605 but i realized i need a capacitor tester, since its electrolytic supposedly you can't use an ohmmeter. I also took out the transformer but since it has so many levels im confused on how i would test with an ohmmeter. I see that alot of the people on this forum are have similar problems with this model. If you look at the transformer on the power supply schematic it shows that pin number 8 is grounded, but on my board there isn't a solder pad and its just stuck through a hole and it looks done on purpose. Man i thought i was getting decent after fixing an samsung tv and an bass amp but this is kicking my ass.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

Bump

[budm]

Re: Phillips 32pfl3504d/f7

Still no pictures?

[HairyManBack]

Re: Phillips 32pfl3504d/f7

I can now, do I need to put the components back in? I just have 1 cap, the transformer, and the rectifier diodes out.

[randtek]

Re: Phillips 32pfl3504d/f7

It would be better to have all of the components on the boards for your photos. It is generally best to reinstall parts once you determine them to be good.

You might want to check SA601 to see if it may be shorted.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

Ok well I'll work on that. I'll have them up I. A few hours.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

This is the board

[HairyManBack]

Re: Phillips 32pfl3504d/f7

This is the part that was blown in half (27 watt Zener) it's been replaced

[HairyManBack]

Re: Phillips 32pfl3504d/f7

Here is a pic of the bottom of the solder board where the transformer is soldered in. On the schematic it shows that pin 8 is connected but on the board there is no solder pad. But pin 9 has a solder pad but pin 9 on the transformer is not connected to the transformer. I will have a pick of the transformer to show you.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

Here is the power supply side of the transformer. Notice how pin 8 is connected by wire but pin 9 is not.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

Here is a pick of the bottom.

[budm]

Re: Phillips 32pfl3504d/f7

For that Zener D606 (Gate protection for the MOSFET Q601) to blow up like that, the Gate to Source of the MOSFET may have shorted out, you should check theat Q601, the Source resistor R614, D612.
Do not worry about the pin 8 of the transformer, it is the way they label/count the pin, since it works before the circuits blew up, I would not wory about that.

[tom66]

Re: Phillips 32pfl3504d/f7

More likely gate-drain.

However, the zener can sometimes fail because it runs very hot (self-oscillating power supply, no control IC.)

[HairyManBack]

Re: Phillips 32pfl3504d/f7

I replaced that MOSFET up there. I didn't have any resistance any way I put the leads on my ohmmeter so it was open.

[HairyManBack]

Re: Phillips 32pfl3504d/f7

When I replaced that one Zener I went ahead and replaced the other two just in case. I also replaced both of the switching diodes which one of them was open. I think it was d611, I can't remember for sure.

[budm]

Re: Phillips 32pfl3504d/f7

Typo, it should be Gate and Drain.
So are you getting any DC at pin 3, 5 of the transformer? Source resistor OK? Q602?
There are three 390K resitors in series which is used for the current limiting and for kick start to Bias on the Q601 when it is first power up, the the positive feedback from the winding at pin7 of the transformer will drive the Gate through the RC network, the 27V Zener is used to make sure the feedback signal will never get to more than 27V. Q602 is used for controling how much voltage is being fed to the Gate basde on the negative feedback of the opto IC601, if the DC out put on the secondary side goes up, the LED in inside the opto will be bias on more, so the opto transistor in the receiving side will be bias on more which will bias the Base of Q602 more which will divert the feedback voltage to the Gate through ground whick will make Q601 drive the transformer T601 less, so the output DC on the secondary will drop back down to the regulation point again, the opposite haapens if the DC output goes low, very simple setup.

[tom66]

Re: Phillips 32pfl3504d/f7

Interestingly the feedback winding also provides a very high current to charge -and- discharge the FET's gate using the slow ramp of current on the primary which occurs as the FET hits the Vgs(th).

BTW the gate voltage will often exceed the 27V threshold of the zener due to the high gate pulse current (several amps.) This kills the zener, unless the transformer is properly designed... which it often is. Also, this can damage the FET.