Need schematic for Visio LC420

[budm]

Re: Need schematic for Visio LC420

One of the pictures I attempted to post shows the power board to system board connection and labeling of the connector. However since none of these will post for some reason. Beginning with Pin one, the pins are labeled:
5.1VSB PIN1-3 measured 5.2vd
SGND PINS 4-7 measured 0vdc
12V PINS 8-11 measured 12vdc
PSON PIN 12 measured 1.17 vdc
I-ON/OFF PIN 13 measured 0vdc
LAMP PIN 14 measured 0vdc
DIM PIN 15 measured 0vdc

PLEASE DISREGARD THE EARLIER VOLTAGE READINGS POSTED, very sorry for being so sloppy in my reporting. I am still trying to figure out why no none of the pictures are being posted. Thanks so very much. My system board is not available at SJ.

1) 'PSON PIN 12 measured 1.17 vdc': This looks to be too low, I expect >2V DC. Does it change state when you toggle the TV on and off? Notes: some power supply does use >1V for = ON signal.
2) '12V PINS 8-11 measured 12vdc': Does this toggle between 0 and 12V when TV is toggle on and off.
3) 'I-ON/OFF PIN 13 measured 0vdc': Main board is not sending the I-ON/OFF (BL-ON) to turn on backlights circuit.
4) 'DIM PIN 15 measured 0vdc': Main board is not sending Dimming control signal to the backlights circuit.
5) You indicated that the DC V between the two legs of the main filter cap is only 325V DC, I expect around 380 ~ 400V DC when PS-ON is present.

[jkb242]

Re: Need schematic for Visio LC420

2: that does not look like Vizio TV model number. That sounds more like the LCD panel model number.
2: if you upload good clear straight shot high-res pictures of the whole Top and Bottom side of the board then you may get more help.
3: I doubt that we will find the schematic of the power supply board, it is made by the third party.
What Voltages did you test on the power supply board so far?
The more details you provide the more help you will get.

Budm
The two surface mounted fuses you inquired about are as you stated, 12.2vdc and 5.2 vdc andare indeed good. There is a third fuse close by but it has no voltage either side with AC power connected. Without a schematic, I have no way to determine its function.

[budm]

Re: Need schematic for Visio LC420

Please provide the close up in that third fuse section, it looks to be some kind of switching power supply, that may be the cause of the problem beside low PFC Boosted Voltage of only 325V DC.

[budm]

Re: Need schematic for Visio LC420

Repair kit for the main board: http://www.shopjimmy.com/vizio-3642-...for-e420vl.htm
Look at that section of the third fuse to see one of those IC on the list is in that section or not. U14, U33.
Get the P/N as printed on top of those two IC's.

Vizio 3642-0872-0150 (0171-2272-3253) Main Board for E420VL
http://www.shopjimmy.com/vizio-3642-...for-e420vl.htm
It looks like U33 is in that section where the third fuse is!

[jkb242]

Re: Need schematic for Visio LC420

1) 'PSON PIN 12 measured 1.17 vdc': This looks to be too low, I expect >2V DC. Does it change state when you toggle the TV on and off? Notes: some power supply does use >1V for = ON signal.
2) '12V PINS 8-11 measured 12vdc': Does this toggle between 0 and 12V when TV is toggle on and off.
3) 'I-ON/OFF PIN 13 measured 0vdc': Main board is not sending the I-ON/OFF (BL-ON) to turn on backlights circuit.
4) 'DIM PIN 15 measured 0vdc': Main board is not sending Dimming control signal to the backlights circuit.
5) You indicated that the DC V between the two legs of the main filter cap is only 325V DC, I expect around 380 ~ 400V DC when PS-ON is present.

Answer to your questions regarding 1.17vdc and 12.2vdc if these change when pressing the power button, no they do not always present as long as AC power is applied.

[budm]

Re: Need schematic for Visio LC420

Same for the 325vdc on the main cap? It sounds like the Main board is stuck.
I would get the repair kit.
BTW, you may have problem with two boards: PS and Main bd.

[nomoresonys]

Re: Need schematic for Visio LC420

I'd test the powersupply by itself per video in post #14, see if filter cap voltage comes up or any other voltages change.

[jkb242]

Re: Need schematic for Visio LC420

The repair kit you mentioned, any idea as to what it includes? I don't mind repairing the board but just concerned as to what components are included given the very many different parts of the ,aim board.

[budm]

Re: Need schematic for Visio LC420

Link in my post 24 tells you what are in the kit.

[jkb242]

Re: Need schematic for Visio LC420

POSTING UPDATES TO THIS THREAD REGARDING NEW FINDINGS

Thanks to all who have taken the time to review the previous discussions adding their input, I appreciate this so very much.

The model of this set is E420VL not the original one stated which was a mistake in my part. Focus has been on the System board over the last several days checking voltage regulators, and chips containing dual MOSFETS. Since I have no schematic it's the only thing I can do for troubleshooting.

ORIGINAL ISSUE: no start, set dead with 5.0sb, & 12v, no BL no video no audio.

Testing system board alone using dual power supplies to provide 5.0 and 12v, with PSON 3.3, LAMP 2.58, no DIM or on/off voltage present on power supply harness pins connecting system board.

U33 and EEPROM replaced sourced from SJ SUPPLY.

Note the attached picture specifically the area of the two 220μh coils. This area is contains a red arrow on the board. U33 has sources voltages for both MOSFETS but no corresponding drain voltages on either. This is a new part from SJ. The fuse in this area also measures continuity but no voltage. I feel this could be a major part of the issue but with no schematic, it's diffucult to trace the supplying sources but it appears to be U33. Could someone with a schematic or familiarity with this circuit please comment as to the missing Drain voltages.

Thanks

[jkb242]

Re: Need schematic for Visio LC420

Before I come to request assistance, I would like to do my own due diligence fin troubleshooting this dead set. If someone has a schematic of the power board or the entire set I would greatly appreciate so very much. I love this forum and site it's the only one I follow for years.

Thanks so very much in advance!,

POSTING UPDATES TO THIS THREAD REGARDING NEW FINDINGS

Thanks to all who have taken the time to review the previous discussions adding their input, I appreciate this so very much.

The model of this set is E420VL not the original one stated which was a mistake in my part. Focus has been on the System board over the last several days checking voltage regulators, and chips containing dual MOSFETS. Since I have no schematic it's the only thing I can do for troubleshooting.

ORIGINAL ISSUE: no start, set dead with 5.0sb, & 12v, no BL no video no audio.

Testing system board alone using dual power supplies to provide 5.0 and 12v, with PSON 3.3, LAMP 2.58, no DIM or on/off voltage present on power supply harness pins connecting system board.

U33 and EEPROM replaced sourced from SJ SUPPLY.

Note the attached picture specifically the area of the two 220μh coils. This area is contains a red arrow on the board. U33 has sources voltages for both MOSFETS but no corresponding drain voltages on either. This is a new part from SJ. The fuse in this area also measures continuity but no voltage. I feel this could be a major part of the issue but with no schematic, it's diffucult to trace the supplying sources but it appears to be U33. Could someone with a schematic or familiarity with this circuit please comment as to the missing Drain voltages.

Thanks

[jkb242]

Re: Need schematic for Visio LC420

VERY SORRY, UNINTENDED DOUBLE POST OF LAST UPDATE.


SITE ADMIN PLEASE REMOVE.

Thanks

[budm]

Re: Need schematic for Visio LC420

So what is the P/N of U33?
The spec sheet of the IC may have application notes circuit showing how to use the IC.

[jkb242]

Re: Need schematic for Visio LC420

hi Bud, I will set back to you on that in just a bit it's a dual MOSFET good suggestion though.

[jkb242]

Re: Need schematic for Visio LC420

Bud, U33 is a Fairchild FDS4953 P channel requiring -5v to -10v for the source to drain resistance to be 55mohm. Don't believe the gate voltage source is present.

[budm]

Re: Need schematic for Visio LC420

OK, it is P-CH and the + Voltage is fed to the Source pins as expected, so for the MOFETs to be on the Gate Voltage has to BE AT LEAST 3V less than the Source pin.
So what is the Voltage on the Gate pin with ref to the circuit GND?

[jkb242]

Re: Need schematic for Visio LC420

Bud; on the power supply board, there is a bipolar transistor that is used several times for pull up or down but cannot find them anywhere. It's bears the marking as 702H. Got any idea where these might be sourced. Have one that appears to have open base-emitter juncruon. This connects to the PSON pin where this voltage is missing from original measurements.

[budm]

Re: Need schematic for Visio LC420

Bud; on the power supply board, there is a bipolar transistor that is used several times for pull up or down but cannot find them anywhere. It's bears the marking as 702H. Got any idea where these might be sourced. Have one that appears to have open base-emitter juncruon. This connects to the PSON pin where this voltage is missing from original measurements.

At this point I will not be concerned with power supply because the PS-ON signal is high enough for the switched 12V to come on, I would work in that main board section where the U33 Dual MOSFETs to see what Gate Voltage you have. Right now we know that the main board is not sending BL-ON, DIM control signals.

[jkb242]

Re: Need schematic for Visio LC420

Right, and know this circuit is critical to the issue.

Thanks

[jkb242]

Re: Need schematic for Visio LC420

At this point I will not be concerned with power supply because the PS-ON signal is high enough for the switched 12V to come on, I would work in that main board section where the U33 Dual MOSFETs to see what Gate Voltage you have. Right now we know that the main board is not sending BL-ON, DIM control signals.

Bud, the dual MOSFET U33 is connected in parallel on the board. The gate is driven by an NPN the collector, the base is fed from the main processor chip. A positive going pulse or high would cause a low st the gates. This is obviously not happening since the drains are showing 0vdc. Just an update at this point but the main board is NIT connected to the power board, instead the 5.1v and 12v Raul's are being supplied by two separate P/S connected to the same point as normally supplied by the power board.

Thanks