General ? concerning PS_On and other DC voltages from PS to MB

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

That resistor has he same 1.2 voltage on both sides.
q1 and q2 seem to have 0.663 volts on the lower right pins, so they are splitting the voltage? I replaced Q1 earlier but no difference. did not replace q2.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Q1 looks to be driving the U1.
What DCV do you have on the Collector of Q2, Q5, and Q7?

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Q1
Collector 0v
emitter 0v
Base .661v

Q2
Collector .661v
emitter 0v
base 0v

Q5
collector 3.2v
Emitter 0v
base 0v

Q7
Collector 0v
Emitter 0v
Base .637v

All the pins on the right side of U1 are all 5.06 volts pin 1 and 4 on left side are also 5.06 volts and pin 2 and 3 are 0v don't know if that helps at all.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Also just for fun, I went back to see what the voltages would be when forced on with the main plugged in, and the tv did not turn on this time. Well I had all the PSB voltages but the no backlight no picture.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Q1, this transistor is BIAS on so Collector is 0V
Collector 0v
emitter 0v
Base .661v

Q2: this transistor is NOT BIAS on so Collector should be at 3~5V depends on VCC. It is not right
Collector .661v
emitter 0v
base 0v

Q5: this transistor is NOT BIAS on so Collector is 3.2V
collector 3.2v
Emitter 0v
base 0v

Q7: this transistor is BIAS on so Collector is 0V
Collector 0v
Emitter 0v
Base .637v

All the pins on the right side of U1 are all 5.06 volts pin 1 and 4 on left side are also 5.06 volts and pin 2 and 3 are 0v don't know if that helps at all.

Remove Q2 and see what DCV you get at the Collector pin.
We are getting so close to where the problem is, just have to locate them switched transistors.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Same thing .661 at collector when Q2 is removed

Also wanted to make sure but you did see post 24 correct?

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Yes that is because the pin 1 on the main board is not allowing PS-ON to go high, it is pulling down the Voltage that you forcing on (you did use resistor for force on right?) if you tie the PS-ON pin to the STBY Voltage directly and then plug in to the main board, the device on the main board can be damaged.
'Same thing .661 at collector when Q2 is removed' so if you check PS-ON on pin 1, do you still see 1.2V, if you do then Q2 may not be related to the PS-ON signal path.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

No resistor used but it still turned the set on and I did turn it right off after no more than 5 seconds of it being on.
Q2 removed and we still got the 1.2v so it seems like it may not be related to the signal path.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

No resistor used but it still turned the set on and I did turn it right off after no more than 5 seconds of it being on.
Q2 removed and we still got the 1.2v so it seems like it may not be related to the signal path.

OK, you did not damaged anything.
So you will have to some how find out where that 1.2V is coming from, it is going to be time consuming but we need to find it.
Other trick that may be used is to find an active pin that goes high and stay high when power switch is turned on and goes low when power switch is tuned off and use that as the PS-ON signal source.
I hate to replace the main board if is due to just a bad switching transistor some where.
So none of those 4 transistor E-B Voltage change state when TV is turned ON and OFF?

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Nope huge edit
So with it out of circuit, I get the same voltage on that collector pin, but in this post that I just deleted and am editing, I said all voltages stay the same whether the power button is turned on or not. That was a mistake. All voltages on all of those transistors drop to 0 when I press the power button.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

I am confused now.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Sorry budm, I had a big work day yesterday until 3:00AM and a pretty big day today as well so I am not thinking properly. I am done for the weekend and will get back to the shop monday so that we can start fresh. Sorry. Thank you for helping as well.

-Nick

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Ok I am ready to tackle this guy again. So this time with a resistor in place, I am still able to get the tv to turn on and show proper video so no damage done. Same thing I only let it stay on for about 5 seconds and then shut it off after I could tell the tv was on with logo and all. However I obviously have to force on the set for it to come on.
Back to the last post.
When I first plug in the set, all voltages on transistors Q1 Q2 Q5 Q7 are all at 0v on all legs. Once the set is turned on, they go to the voltages posted earlier. After pressing the power button again they drop back to 0vdc.
Now in an earlier post you had stated
"find a pin that goes high and stays high when power switch is turned on and goes low when power switch is tuned off and use that as the PS-ON signal source."

So are you talking about a 3.3v line and just shorting the PS-ON line to that? Or do you mean use it to back track to other components?

Sorry for taking so long on this one, but thanks for sticking with it. Very much appreciated!

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

OK, just to be clear on the Q5 Collector DCV reading when the TV is off, it is at 0VDC and when the power switch is turned on then the Q5 Collector DCV goes up to 3.2V as indicate in post 23. Correct?

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Yes that is correct. Just rechecked right now.

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

OK, remove the force on resistor you have on the PS-ON wire, then connect one end of 1K resistor to the Collector of Q5, the other end of resistor will be connected to that PS-ON wire, what we are doing is to use the Collector Voltage of Q5 as the PS-ON signal to turn on the power supply.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

Sorry had to wait for the iron to get hot to solder a wire to the resistor. But yeah it works as if the tv was working normally.

Where do you think we should go from here?

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

The hardest problem right now is to locate the path of that PS-ON pin signal line to where it goes to, you may ending up spending lots of time trying to locate the connections or use it as is with this mod for now, at least the power supply will go into OFF mode when TV is turned off instead of being on all the time using the force on resistor.

[Nick's Tvs]

Re: General ? concerning PS_On and other DC voltages from PS to MB

would it be safe to use with the mod? How long would that last?

[budm]

Re: General ? concerning PS_On and other DC voltages from PS to MB

The mod should work fine and we barely drawing any current through the Collector resistor, only about additional 3mA.
Since one function of the board already failed, then it have some other section that may fail later on, I would it until it dies before spending the money on new main board.
You have already verify ALL the TV functions work, right?