Proscan 42LA45H PSU Problem

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Nevermind, I'm retarded apparently. Thought I had to measure the voltages from the bottom of the board and realized that I could do it from the top. Have attached the pic with the measured voltages. I could not reach VCC2 from the top, but there was a bare wire on top (W808) going to it that read 0.26v.

[budm]

Re: Proscan 42LA45H PSU Problem

You can test the board by itself, I am NOT sure if this board has pull -up resistor for the SW (PS-ON) pin or not.
Try powering it up by itself and take the Voltages readings on those same pins to see what you get. You may need external pull-up resistor.
To be safe you should plug the board into GFCI outlet to protect your self.

[budm]

Re: Proscan 42LA45H PSU Problem

Nevermind, I'm retarded apparently. Thought I had to measure the voltages from the bottom of the board and realized that I could do it from the top. Have attached the pic with the measured voltages. I could not reach VCC2 from the top, but there was a bare wire on top (W808) going to it that read 0.26v.

So that is the reading with the SW (PS-ON) pi sitting at >3VDC?
Are doing the test with just the power supply board by itself?
BTW, the DCV on that SW pin, does it change state between <1V and >3VDC when you toggle the power switch on and off.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Yeah, the reading on the out pin was < 3vdc and the in pin was 5vdc. It was not with the supply only. I just plugged it back in to the TV like it should have been and tested the voltages at the pins coming out of the components. I didn't toggle the switch at that time, but I just did and got the same readings.

On a side note, while checking the voltages I accidentally shorted the in to the out on the m5v relay and the LED light at the bottom of the board came on. I guess that means that the relay isn't getting the signal it needs to open?

[budm]

Re: Proscan 42LA45H PSU Problem

M5V device is the MOSFET not relay, it is used as electronics switch to supply M5V pin, the input pin of the M5V is from the S5V (VCC1) which you have already. The VCC 2 which is connected to the 24V which is used for that SMPS for the 12/5V output, the 28V are also generated by the large transformer T801.
The SW signal is used to turn on the M5V, and also the 12/5V and the 24V which is not on right now as you can see that you do not have Voltage at VCC2.
I am trying to verify if the DCV at the SW pin is toggle HI and LO or not when you activate the power switch ON and OFF, so does it change state when you toggle the power switch on and off?

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

When I pushed the power switch the values did not change at all

[budm]

Re: Proscan 42LA45H PSU Problem

OK, now I am beginning to think that this power supply board may be using active LO to turn on the power supply (LO = ON). So try this, run the power supply board by itself and then check the DCV in the SW (PS-ON) Pin and GND pin to see what you have, then check the DCV between M5V and GND to see what you have.
I am having hard time tracing the SW (PS-ON) signal traces to see how it turn OPTO ON and OFF.

[budm]

Re: Proscan 42LA45H PSU Problem

OK, I figured it out now, it is active HI, the OPTO is turned by transistor V816 which is turned on when the SW (PS-ON) signal is HI.
So we need to check the Vf of the LED inside the OPTO N805 pin 1 and 2, it should have >1VDC when SW (PS-ON) signal is present.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Ok, I didn't really understand what you said there but I got the gist of what you needed from me I think. I tested voltages at V816 and results are in the pic. Might as well be 0vdc on both sides. I also tested voltages at N805. I didn't know what pins were 1 and 2 so I measured them all. The two pins on the cold side read fine and results are in the pic. The two pins I tried to measure on the hot side must be VAC not VDC because my little meter went all wonky when I tried to get the voltages off those ones.

I tried all of these voltages while the power button was not being pressed first, and then again while pressing the power button. No values changed on any of the pins I tested.

If that wasn't what you needed please let me know.

[budm]

Re: Proscan 42LA45H PSU Problem

OK, the hot side of the OPTO, you will need to measure in DCV between the two legs of the OPTO, not with ref to GND, it should be <1VDC if the OPTO is turned on.
Do you know the history of this TV? Was it hit by surge or something? It is not good sign that the SW signal is not toggling which means there is also problem with the main board.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Ok, when I measure the hot side of the OPTO like you described its reading ~9.8VDC when I push the power button and when I leave it alone.

I don't know the history. Just found it out by the dumpster and had hopes of fixing it on the cheap. Screen and everything looks pristine and I can't see anything visually wrong with the main board. I have not removed it and looked at the back of the main board, however.

[budm]

Re: Proscan 42LA45H PSU Problem

Ok, when I measure the hot side of the OPTO like you described its reading ~9.8VDC when I push the power button and when I leave it alone.

I don't know the history. Just found it out by the dumpster and had hopes of fixing it on the cheap. Screen and everything looks pristine and I can't see anything visually wrong with the main board. I have not removed it and looked at the back of the main board, however.

OK , that OPTO is not on, if it is on the DCV between those two legs (the output pins) should be <1V when you have >3VDC at the SW pin. So far it does not look good, the main board is not working right, the SW (PS-ON) is not activating the OPTO.
BTW, did you get the P/n of those two devices? The SMPS (BUCK REGULATOR) and the MOSFET for switching the M5V.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Yeah, I took pics and posted them (#19) earlier. But I'm definitely getting a bunch of voltage on the hot side of that OPTO and little to none on the other side of it.

[budm]

Re: Proscan 42LA45H PSU Problem

Yeah, I took pics and posted them (#19) earlier. But I'm definitely getting a bunch of voltage on the hot side of that OPTO and little to none on the other side of it.

OK, sorry about that. I found the data sheet for LM2576-ADJ, and the Power MOSFET NTD4809.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Those data sheets are Greek to me man, lol. They appear to be the right parts, but that's all I can say

[budm]

Re: Proscan 42LA45H PSU Problem

So right now basically the MOSFET (NTD4809) for the M5V is not turned on to provide the M5V output, the OPTO is not turn on (pin 3 and has 9.8VDC) with SW (PS-ON) signal present.
I can only do so much tracing of the circuits from the pictures, we need to look at the SW (PS-ON) section to see what is going on.

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

I have to run some errands, but I will be back later tonight and we can go from there. I'll take a look and see if I can puzzle anything out as well. Would help if I understood how it works

[Nr1Ctr]

Re: Proscan 42LA45H PSU Problem

Would there be any possible issues if I shorted the in pin (5v) of that MOSFET to the out pin on the MOSFET? I accidentally did it before and the led lit up like the board was good to go. Just doing this to see if the set would actually turn on. Don't wanna burn something up tho.

[budm]

Re: Proscan 42LA45H PSU Problem

Would there be any possible issues if I shorted the in pin (5v) of that MOSFET to the out pin on the MOSFET? I accidentally did it before and the led lit up like the board was good to go. Just doing this to see if the set would actually turn on. Don't wanna burn something up tho.

You can force it on that way but you still need to get the 24V, 28V, and the 12/5V power supply section to run too. you can try bridging pin 3 and pin 4 (in the hot side) of the PS-ON OPTO to see if those power supply will come on.
Do all of this with just the power supply board by itself.

[nwcs]

Re: Proscan 42LA45H PSU Problem

Did anyone ever get a answer to this problem. I have the identical problem with this tv and would like to isolate it.