Vizio VW42LFHDTV10A

[Chancey]

Re: Vizio VW42LFHDTV10A

ok...traced it back.
R3 - 553 ohms
to the collector of Q1
Collector to base measurement, on diode scale, show's .500 (maybe good)

I'd say that Q1 and Q32 are setup in a push pull, but cannot read the writing on the face of the surface mounts to tell if PNP and NPN. Q32's Collector traces out to Q1's Base. Traced the Emmiter on Q1, it ties to the collector on Q1 and passes back to R315. Ironically, R315 ohms out to 666 ohms. ?! You can see on the picture's I included...

Just checked where the trace goes under silk screen R383...it goes to the audio amplifier through the trace that connects to the speakers connector J5 pin3. I traced it back and it goes direct to pins 2, 7 and 15. The trace also loops around and goes to pin 14. Page 2 of the included PDF shows 2, 7 and 15 are all grounds and 14 is audio out for channel 2-.

Every other trace leads back to CPU. :/ Sounds like, if it's not those two surface mount transistors, I'm looking at replacing the main board. Just curious if I was on the right track...

[budm]

Re: Vizio VW42LFHDTV10A

"Collector to base measurement, on diode scale, show's .500 (maybe good)" You mean Base and Emitter? or Collector to Emitter?
OK, Q32 is an inverter, it inverts the output of the CPU, Q1 is also inverter, it inverts output of Q32.
This is what it should be when the TV is OFF:
Output of the CPU will be LOW so Q32 will be OFF, its Collector voltage will be HIGH which will turn ON Q1, which will make its Collector voltage go LOW (PS_ON = LOW) thus the power supply will stay OFF.
When you turn on the TV:
Output of the CPU will be HIGH so Q32 will be ON, its Collector voltage will be LOW which will turn OFF Q1, which will make its Collector voltage go HIGH (PS_ON = HIGH) thus the power supply will turn ON.
So check the voltage between E and B of Q32 when the TV is OFF, and when TV is ON, you should see it changes state.
See the diagram.

[Chancey]

Re: Vizio VW42LFHDTV10A

So basically, it's a complex NOT gate. Checking the voltages...will edit this post to give readings.

Making new post so it will bump...

[budm]

Re: Vizio VW42LFHDTV10A

Just think of those two transistor as two inverters hook up in series

[Chancey]

Re: Vizio VW42LFHDTV10A

Ok...I think I understand that, takes one to be saturated for the next one to work.

Ok, my findings are:
Voltage isn't coming from CPU (wish I could get the heat sink off to see which pin it goes to, but looks like a BGA), it looks like it is coming from the out2- on the audio amp at 3.3vdc. Not sure if that's suppose to be the trigger...but I have some concerns about that. The voltage is stepped down to 1.5 when off and shows short when set comes on (where the trace goes to the CPU)

The voltage readings on Q32 Emmiter to Base shows 0 volts, off and on. however, base to collector and emmiter to collector shows .66vdc. I tried to find a datasheet on the transistor to see what saturation voltage would be, but even if .66 was saturation/breakover, it wouldn't be enough to trigger Q1.

I doubled checked on diode scale and did get this reading: neg probe on C and pos probe on B, .600...E to B .700...C to E on Q32 shows .7 as on Q1 show 1.7. I thought bout what you said, it could be that the meter having diode scale and continuity on the same selection is why it's giving that reading cause there shouldn't be a diode between collector and base, that would be the digital switch after saturation, right? LOL, I struggled on the transistor part in college...something that should've been simple, like darlingtons and such kicked my rear. However, might have been the way I was taught. So back to the C to B...might be internal resistance. But from c to E on both...there is a noticeable difference.

I think this may be the datasheet...the writings on the transistor show ZCA with an A1 written vertical on the side. If you lay the trans flat and count left to right, bottom left is base, top middle is collector, bottom right emmiter

[Chancey]

Re: Vizio VW42LFHDTV10A

Sorry...posted without including the pdf I found.

[budm]

Re: Vizio VW42LFHDTV10A

The key point is that the E-B voltage of Q32 has to be at 0.6V to turn the on Q32, right now Q32 is OFF so it bias on Q1. Q32 is not getting the state of change at its Base.
The transistors are NPN, so just think of the transistor has two Diode inside with common cathode at the Base. If you have meter set to Diode test, black probe to BASE, then Base to Emiter, Base to Collector will show conduction of 0.6V on your meter.
When you check E to C of Q32, you are actually reading E-B junction of Q1, see the diagram. The transistors are OK, the problem right now is that Q32 is not getting the correct voltage when TV is turn on.
"If you lay the trans flat and count left to right, bottom left is base, top middle is collector, bottom right emmiter" that is correct and it matches the silk screen on the PCB as shown in your picture.

[Chancey]

Re: Vizio VW42LFHDTV10A

Ok...from what I have gathered by checking the traces, over and over again...your diagram is 100% dead on. The signal is not comin from the processor through R4...on or off. I have read in other post's to trace power on switch to CPU to make sure the correct voltage is getting to the CPU to toggle that input. Other than that...I'd say the main board is dead. All roads lead back to the CPU...budm, by far, you have to be one of the most knowledgeable individuals I have had the pleasure to communicate with and I thank you for your time. I'm gonna look and see what happens when the switch is toggled on and trace all that out...other than that, I'm gonna break the bad news.

[budm]

Re: Vizio VW42LFHDTV10A

One thing is that when you force the TV on by using the jumper and ALL the TV functions correct, that mean the output pin of the CPU PS_ON control is bad but everything else is OK.
This is how the TV functions: when you trun on the TV, it will go into self test mode, then it will send the PS_ON signal first to supply the 24V to the inverter circuits and 12V for the Audio, after short time the main board will send the signal to turn on the Inverter to produce the backlights, the reason that they do not turn on the 24V at the same time as the inverter is that it does take a period of time for the 24V to be stable if you try to turn every thing on all at the same time, the voltage is not stablized yet which can cause startup problem or strain the circuits, that is why things are turn on in sequence. There is a way to add the circuits so the PS_ON will be on first by using the Inverter on signal to turn on the 24V first, that same signal will go through a delay circuits with a slight delay to turn on the Inverter.

[Chancey]

Re: Vizio VW42LFHDTV10A

:/ I'm at a loss for the signal flow of power on and the inverter on. I understand what you described, as the sequence of event's and possibly the time delay fuses slowing how the system powers up. But, I cannot use A1 if it's brightness right? Because that would cause the system to be unstable or even power off if they lower the brightness of the TV. As far as building a circuit, I could possible do that fairly easily. Where would be the first place I should look, I cannot get the heat sink off, so finding a datasheet for that CPU to find INV_ON wouldn't b much of an option....unless all mainboards of this manner use the same CPU. I'll check that avenue. But could you iterate on adding the circuits. Would that be as simple as cutting the trace going to R4 and placing a jumper from INV_ON to there? However, I don't have any Kynar wire...or 32 gauge. Well, that wouldn't work if INV_ON wait's for PS_ON. LOL...I feel like I'm chasing a ghost.

[budm]

Re: Vizio VW42LFHDTV10A

The A1, B1, C1: One these 3 lines is the INVETER_ON (or BL_ON). On the On the Inverter board connector should have the label on it to indicate the pin out, one of them should be something like ON/OF, or INVERTER ON/OFF, or BL_ON. I believe that is the line you are using to jump the power supply, just need to verify it.
The circuits will involve a couple inverter circuits (using two transistors) with and added RC (Resistor/Capacitor). Or use a time delayed relay.
No cutiing tape involve, we just going to use the BL_ON line that feeds the inverter board (through the power supply board) and route that to the PS_ON pin of the power supply, the PS_ON wire from the main board will be disconnected and not used any more. The PS_ON pin will have one wire add to it, this wire will feed the delayed on circuits, the output of this circuits will feed the BL_ON pin on the Inverter board.
So find the BL_ON PIN on the inverter board first.

[Chancey]

Re: Vizio VW42LFHDTV10A

C1 is not populated...pin 14 (status)
Removed Inverter board to see silk screen...
Pin 13/B1 - Vbr-B
Pin 12/A1 - Vonoff

Ironically, A1 was the pin I was jumpering off of.

[budm]

Re: Vizio VW42LFHDTV10A

That is the right pin we need to use.

[Chancey]

Re: Vizio VW42LFHDTV10A

That is the right pin we need to use.

Kind of curious if I need to build the inverter...that pin doesn't go HI till power switch is pressed. I think I understand what you're talking bout doing...cut the trace on A1 leading to inverter, re-route that trace to PS_ON, pull wire from main board for PS_ON from J1 and reroute that wire to transistor inverter with time delay for A1/Vonoff on LG Inverter. Time delay relay's though...would they function at such a low voltage? Or pull off 12v feeding back to main board and use the old PS_ON wire as common and wire A1 with N/O side of delay? Doing something like that would be easier for me than building the circuit and making sure I get everything perfect.

Debating on letting the guy know that the main board is gone and see if he wants to pay for a new board or allow me to do this instead. :/ debating....what do you think about the time delay relay rather than the transistor inverter

[budm]

Re: Vizio VW42LFHDTV10A

Please see the simpify diagram. You got the idea what I try to do. We will be using +5V standby to power this delayed circuit.

[Chancey]

Re: Vizio VW42LFHDTV10A

In the first schematic, wouldn't that turn the backlight on with TV in standby? Or the inverter will always be high waiting on the power button to be pressed with 5vstby going through the 1k resistor before the collector? Just curious if i was viewing that correctly...I realized that the 24v will not be present until PS_ON is satisfied.

[budm]

Re: Vizio VW42LFHDTV10A

When TV is OFF, A1 (INVERTER ON or BL_ON) output from the main board will be LOW (that also means PS_ON which is now connected to the BL_ON line now instead will see low so 12/24 will be OFF), which will cause MOSFET 2N7000 to OFF, the voltage at Drain will be high which will turn 2N2222 ON, that will make its Collector to be LOW so the Inverter connector ON/OFF PIN which see LOW which will keep the inverter OFF. When power switch is turn on, A1 will go high which will turn on the 12/24V power supply ON, this high at A1 will charge up capacitor through the Gate resistor until it reach the Gate turn on voltage, which will make Drain voltage to go low which will turn off 2n2222, which will make its Collector voltage go high which will turn on the inverter circuits. The 5VSTBY is always on which is there the minute you plug your TV into the outlet.

[Chancey]

Re: Vizio VW42LFHDTV10A

Did I say that I sucked it up in college on AC and transistors? I'm learning...

[budm]

Re: Vizio VW42LFHDTV10A

If you are going to go this route, build the delay circuit on the bread board first to test it out. You can run it off batteries.
Oh one another thing, can you trace out A1 pin to see if it is also connected to the transistor on the Main board similar to the PS_ON circuit that you took the pictures?

[Chancey]

Re: Vizio VW42LFHDTV10A

I'll get to that one tomorrow...been busy. Made a nice circuit with ACAD from your drawing. Debating on SMD for all except 2n2222. Small and out of the way...