Dead 42pfl3605/h12 but some voltages

[anna1980]

i got here a 42pfl3605/h12 which is not quite dead
When plugged in to power the blue led on de power board comes on then dims en blinks until off

I measured the different voltages on the connector to the mainbord and only measured a good 12v
the 5v rails measured 3 volts , the s/b voltage 1 volt and the 24v measured 21 volts.

When the powerboard is disconnected from the mainboard, i only get an steady 5 volts. No other voltages.

How can i further determine what the problem could be. I can only find two faults with the pfl3605 type tv and those are replacement of DC-DC converter U7106 or replacement of the IC905

And second question. what is the standy (S/B) voltage of this powerboard

[dick_barton]

Re: Dead 42pfl3605/h12 but some voltages

Is this your power supply?

If it is then disconnect the main board and connect the pin with 5V to CN903 Pin 10 (SB) then power up and measure the 12V and 24V voltages

[anna1980]

Re: Dead 42pfl3605/h12 but some voltages

Is this your power supply?

If it is then disconnect the main board and connect the pin with 5V to CN903 Pin 10 (SB) then power up and measure the 12V and 24V voltages

I've taken the board out of the tv. So it's disconnected from the tv itself
After that applied power to it. Got 5 volt on the +5v rail. Disconnected it. Jumped a wire from +5v to S/B and applied power it. Got 5v on the +5v (ofcourse) and 5v on S/B but nothing on the 12v and the 24 volt.

Powerboard is a Z15G3812-P02-H20-003D but the connector CN903 is still the same as yours

[dick_barton]

Re: Dead 42pfl3605/h12 but some voltages

Can you post a clear sharp picture of your power supply board and also the legend alongside the connector.

[anna1980]

Re: Dead 42pfl3605/h12 but some voltages

Can you post a clear sharp picture of your power supply board and also the legend alongside the connector.

Ofcourse I can

[dick_barton]

Re: Dead 42pfl3605/h12 but some voltages

With the mainboard disconnected what voltage do you have on the SB pin and is the +5V at 5V?

[anna1980]

Re: Dead 42pfl3605/h12 but some voltages

With the mainboard disconnected what voltage do you have on the SB pin and is the +5V at 5V?

On both +5v I get 5.32V so that looks okay. On the SB nothing

I tried to trace back the voltage. I assume the SB gets the voltage from the 5v rail so on the back I trace the 5v line. It goes through IC904 (EL817 opto) and then R944 (2.2kOhm resistor). On the drain of q909 (rk7002 transistor) there is still 5v (sometimes somewhat lower) But it ends there. There is no voltage on gate or source.
Shouldn't there be any voltage on gate and source? I could be a bad diode but I have my doubts,; but I could be wrong.

[dick_barton]

Re: Dead 42pfl3605/h12 but some voltages

I believe the SB pin to be the Standby pin and when the +5V is connected to it should bring up the 12V and 24V supplies. It's normal to use a 1K resistor to short the +5V to SB (for safety) to bring the set out of standby.

So with the main board disconnected and the jumper resistor in place at the power supply connector, if you switch on the set the 12V and 24V supplies should be there.

The SB receives the voltage normally from the main board and that switches on circuitry on the power supply to bring up the other voltages.

It must be working since your first post suggests the voltages were there when connected to the mainboard but were lower than expected.

Do you have the correct schematic for the power supply?

[anna1980]

Re: Dead 42pfl3605/h12 but some voltages

I think I got the right one - See attachment

Tomorrow I'll try to get a 1k resistor and test it again

[dick_barton]

Re: Dead 42pfl3605/h12 but some voltages

The connector CN903 does appear to match that shown in the pdf all except for Pin14 (POK) which looks as though your power supply doesn't have that wire connected.

[anna1980]

Re: Dead 42pfl3605/h12 but some voltages

The connector CN903 does appear to match that shown in the pdf all except for Pin14 (POK) which looks as though your power supply doesn't have that wire connected.

Indeed you are right.
But i just connected an 1k resistor from +5v to S/B. Except for the +5v and the S/B no voltages on the other pins.

[Andrew F. Ali]

Re: Dead 42pfl3605/h12 but some voltages

This appears as a PSU problem. Not too sure which component/s are at fault.

[budm]

Re: Dead 42pfl3605/h12 but some voltages

Indeed you are right.
But i just connected an 1k resistor from +5v to S/B. Except for the +5v and the S/B no voltages on the other pins.

If you have 1K resistor connected properly between 5V and SB pin then you should have Gate Voltage of around 3V, so are you getting that?
BTW, when you use the resistor, did you disconnect the cable from the Power supply board to the main board first? It has to be disconnected.

[R_J]

Re: Dead 42pfl3605/h12 but some voltages

In post 1 you said you measured a good +12 volts and +24v was low (+21volts) but now you only have +5 volts?