Phillips 42PFL3704D/F7 No Standby Power

[simcole]

Hello,

So I have a TV (Phillips 42PFL3704D/F7) I've been struggling with. When I plug it in, it does NOTHING. I do not see the 5V standby light. I downloaded the service manual and went to the trouble shooting section for the power supply board. It suggests after checking the fuse to see if "There is any leak or short-circuiting on the primary circuit component and service it if it's defective. (C1205, D1205, D1206, D1207, D1208, Q1203, Q1204, T1201)".

I've taken all the diodes 1205-1208 out of circuit and tested them. They all tested fine. I checked C1205 via a $20 ebay circuit tester w/ LCD screen (LCR-T3 tester). It checked ok too. I finally pulled the Q1203 and Q1204 out and tested them with the same device; the problem is I don't know how to read those results. Here these are:

Q1203 is a FET 2SK3757(Q) pic of it being tested attached below

Q1204 is a Transistor KTC3199-GR-AT/P (says C2120 on part) pic of it being tested attached below

Finally I have NO idea how to test the T1201: TRANS POWER 9705 LTT1PC0KT003

Could one of those 3 things be causing this? If those things are working correctly the next troubleshooting step is "Is the AL+5V line voltage normal?" It is normal and I found that. Also the 3.3v line is normal.

Any help is appreciated.
Finally it says test T1201 which I guess is a

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

Here is a full size picture of the board.. I tried to get it in focus. I made notes on here that you can see in black letters and arrows.

If you look at the diagram I attached (I have the YA1A serial number), I'm getting NO VOLTAGE at the CN1803 white connector. I should be getting panel +24V on pings 1-5 and I'm not. Maybe someone can tell me where else to look now.

[CapLeaker]

Re: Phillips 42PFL3704D/F7 No Standby Power

I hope all the parts are back in the power supply. Plug it in an take your DMM and check the DC voltage on the big filter cap.

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

I hope all the parts are back in the power supply. Plug it in an take your DMM and check the DC voltage on the big filter cap.

So I'm not familiar with the term "Big Filter Cap" but I assume you mean the big transformer T1201. All parts are back in the board and plugged in. I put my DMM common to a cold side ground and ran my red lead to all pins on the DC side from 9-16. I get NO DC voltage of any kind. Is that how I test this thing? Is it bad?

part LTT1PC0KT003. If this is the thing that's bad I can't google a replacement part.

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

Actually if you mean the big black capaicitor on the hot side, I tested that with it plugged in on DC volts. I get no voltage.

Edit: I took it out of circuit and put it in my tester. It tested ok, but I still didn't get voltage AC OR DC on it when it was plugged in.

[philliesfan30m]

Re: Phillips 42PFL3704D/F7 No Standby Power

are you checking that cap with the negative lead on the negative leg of the cap and the positive on the positive leg? when checking on hot side you have to use the negative leg of cap as ground not the chassis. you have to have some kind of voltage on the big cap or you wouldn't be getting any voltage at all.

[philliesfan30m]

Re: Phillips 42PFL3704D/F7 No Standby Power

high voltage there so be careful up to 400vdc

[philliesfan30m]

Re: Phillips 42PFL3704D/F7 No Standby Power

can you post a pic of all of the boards connected

[CapLeaker]

Re: Phillips 42PFL3704D/F7 No Standby Power

Actually if you mean the big black capaicitor on the hot side, I tested that with it plugged in on DC volts. I get no voltage.

Edit: I took it out of circuit and put it in my tester. It tested ok, but I still didn't get voltage AC OR DC on it when it was plugged in.

The filter cap you should be testing is C1201. Did you actually verify that there is no standby voltage? Did you unplug the ribbon cable and measure again?

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

The filter cap you should be testing is C1201. Did you actually verify that there is no standby voltage? Did you unplug the ribbon cable and measure again?

Ok. Yes I tested the voltage by placing negative lead on cap and positive lead on cap as well. I initially tested C1612 which gave no voltage DC

I tested C1201 in circuit and read 171 volts DC. It reads it should be 350V. Ill pull it out of circuit in a minute and test it with my LCD tester.

[CapLeaker]

Re: Phillips 42PFL3704D/F7 No Standby Power

No need. That voltage is correct. 120AC gives you about 170V DC.

Now check C1103 and C1112.

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

No need. That voltage is correct. 120AC gives you about 170V DC.

Now check C1103 and C1112.

C1101 - 3.2vdc
C1103 - 5.2vdc
C1104 - 5.2vdc
C1112 - 13.6vdc

Thanks for the responses so far. I followed the trouble shooting flow chart, but I'm at a loss for now. What next? I'm kinda excited to see what you suggest.

[CapLeaker]

Re: Phillips 42PFL3704D/F7 No Standby Power

Check the bridge rectifier D1601 and see if you get any DC out of it.

The 24V for the backlight wont come on until the power supply is turned on, and the backlight gets the BLon voltage (usually 5V). The STBY voltage is always on at the power supply and feeds the main board. Once you press the power button, that STBY voltage goes back to the power supply and turns on the rest of the power supply rails. So, I think the power supply is producing the STBY voltage, but there might be something going on at the main board not turning on the rest of the power supply. So verify that the STBY voltage reaches the main board. Maybe you find a blown fuse on the main board.
If you connect the main board and the standby disappears, you got a short. If it stays on and no reaction from the main board, something is open or the main chip is fried.


Have a look at page 12-1, 9-5 or 9-6 (depends on your serial number) and 9-7.

So what happened to the TV? A lightning strike special or something?

[simcole]

Re: Phillips 42PFL3704D/F7 No Standby Power

CapLeaker so with the power off I put my mm in diode mode and tested the bridge rectifier in circuit. I was getting .5's across the board which seems normal. When I plugged it in and tested the rectifier I got no AC or DC voltage. When I have all the boards plugged up together i can find my 5v making it across the ribbon cable to the main board. I haven't tried to find it down deeper on that board. The tv was one a neighbor was throwing away and I have no idea what happened to it. I'm trying to give it to my grandmother because she has an old small one and it would be nice to gift her one she can see better.

Talk to me more about what I should see on the bridge rectifier

[CapLeaker]

Re: Phillips 42PFL3704D/F7 No Standby Power

Bridge rectifier D1601 doesn't get any AC until relay RL1201 is energized. It gets it's signal from the main board. Since you are getting 0.5V voltage drop across the 4 legs of D1601, she is all right.

Sounds like you got a bad main board.