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Old 04-06-2018, 08:21 AM   #41
jkb242
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Default Re: Need schematic for Visio LC420

Sorry about the obvious spelling errors. Typing in the iPhone sucks where the characters to the left of the intended character? Proof reading would work too, my bad!
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Old 04-12-2018, 10:11 AM   #42
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Default Re: Need schematic for Visio LC420

UPDATE 4/13/18

After post 31 I shorted across the source drain pins of the dual MOSFET in an attempt to create a normal set on condition or at least a startup ready. This provided a 12vdc rail to the fuse that powers the Mastek MAX17113 multiple voltage supply chip which is assumed to power specific operational voltage bias to other parts of the system board. No schematic so can comment specific connections. The chip powered on normally and produced all voltages of the spec sheet attached except for the 35vdc "go on" as it was too difficult to measure without risking shorting pins. I'll need to remove the system board to confirm if this voltage is present as a pulse or steady when I can measure safely.

Currently I have 3.2vdc on the DIM lead to the power board, 0vdc lamp, 0vdc on I-ON/OFF, 1.16vdc on PSON and of course 12vdc and 5.0vdc stdby.

Would like to know if the power on signal should be higher and the source of this feed. I would like to apply this signal to the LAMP ON terminal of the power board to see if the BL voltage is being generated.

As previously reported, all voltage regulators appear to measure normally.

Much thanks for continued advice and suggestions
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Old 04-12-2018, 10:12 AM   #43
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Default Re: Need schematic for Visio LC420

Dual MOSFET U33
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File Type: pdf FDS4953 Dual 30V P-Channel PowerTrench® MOSFET.pdf (208.8 KB, 1 views)
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Old 04-12-2018, 11:40 AM   #44
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Default Re: Need schematic for Visio LC420

So you bypass the S/D pin of the MOSFET, you could also connect G pin to GND through 100 Ohms resistor to turn on the MOSFET since the micro controller is not turning on the MOSFET at this point.
So now you have 12V on that fuse but the BL-ON is still missing, what you can do is to disconnect the BL-ON wire from the power supply board to the main board first and then use 1K resistor between 5VSTBY and the BL-ON pin on the power supply to force on the backlights, if everything else on the board are OK, except the problem with signal for turning on the MOSFET, then the TV should work.
Right now you have at least two problem, one the MOSFET U33 is not being turned on, two the BL-ON is not present.
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Old 04-12-2018, 12:32 PM   #45
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Default Re: Need schematic for Visio LC420

indeed thanks for the suggestions will try today and report back
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Old 04-12-2018, 04:58 PM   #46
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Default Re: Need schematic for Visio LC420

Bud,

The BL did not come on, but checking the system board "lamp on" lead, (I cut the lamp leadon the harness in half) contains 2.3vdc while the 5.vdc standby in series with the "lamp on" pin on the board shows 0vdc. This confirms this system board signal is being grounded or pulled low on the power board as you mentioned earlier in this thread. I can hunt for the switch on the power board or order a board kit, just hate to shotgun and start changing parts.
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Old 04-16-2018, 03:12 PM   #47
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by budm View Post
So you bypass the S/D pin of the MOSFET, you could also connect G pin to GND through 100 Ohms resistor to turn on the MOSFET since the micro controller is not turning on the MOSFET at this point.
So now you have 12V on that fuse but the BL-ON is still missing, what you can do is to disconnect the BL-ON wire from the power supply board to the main board first and then use 1K resistor between 5VSTBY and the BL-ON pin on the power supply to force on the backlights, if everything else on the board are OK, except the problem with signal for turning on the MOSFET, then the TV should work.
Right now you have at least two problem, one the MOSFET U33 is not being turned on, two the BL-ON is not present.
Bud,

There is an LED on the bottom of the power supply board, what is this for? It appears to be some sort of troubleshooting indicator. Can you assist?

It seems that the "lamp" pin on the power supply board is connected in series with the Anode of a switching diode, the Cathode is connected to the harness leading to the main board. That would suggest that the lamp signal is coming from the main board assuming it is a positive voltage with respects to ground. The diode on the power board is labeled A6, not too informative , at least for me, and it may be a Zener. Connecting the 5SB through a 2.2k resistor to the lamp pin on the power board did not cause the BL to energize.

Can you suggest any other way to confirm that I have a high current AC signal to the transformer which drives the two HV BL coils? Is there anyway to ring the coils with a separate supply or possibly a typical schematic of classical connection of the driver circuit you could attach for me.

Thanks!
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Old 04-17-2018, 01:08 PM   #48
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by budm View Post
So you bypass the S/D pin of the MOSFET, you could also connect G pin to GND through 100 Ohms resistor to turn on the MOSFET since the micro controller is not turning on the MOSFET at this point.
So now you have 12V on that fuse but the BL-ON is still missing, what you can do is to disconnect the BL-ON wire from the power supply board to the main board first and then use 1K resistor between 5VSTBY and the BL-ON pin on the power supply to force on the backlights, if everything else on the board are OK, except the problem with signal for turning on the MOSFET, then the TV should work.
Right now you have at least two problem, one the MOSFET U33 is not being turned on, two the BL-ON is not present.
Hey Budm,

I was wondering if you could confirm a particular test I wish to conduct.

I would like to see if the I can even get an audio input to the main through to the speakers, using the power supply connected to the main board to supply the 5SB and the 12V. Regardless of what is going on with the power supply, I know the 5v and 12v lines are good OR would it be necessary for me to disconnect the power supply and furnish 5v and 12v to the system board for this audio test. If I cant get audio, then the problem on the main board is much larger, like the the main processor. Could you please confirm which audio test would be most conclusive. Thanks!!
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Old 04-17-2018, 09:38 PM   #49
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Default Re: Need schematic for Visio LC420

You can test the power supply/inverter backlights by itself (the cable between the main board and the power supply board MUST be disconnected first) using three 470~1K resistors between 5VSTBY and PS-ON pin, 5VSTBY and I-ON/OFF (BL-ON) pin, 5VSTBY and DIM pin.
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Old 04-18-2018, 12:01 PM   #50
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by budm View Post
So you bypass the S/D pin of the MOSFET, you could also connect G pin to GND through 100 Ohms resistor to turn on the MOSFET since the micro controller is not turning on the MOSFET at this point.
So now you have 12V on that fuse but the BL-ON is still missing, what you can do is to disconnect the BL-ON wire from the power supply board to the main board first and then use 1K resistor between 5VSTBY and the BL-ON pin on the power supply to force on the backlights, if everything else on the board are OK, except the problem with signal for turning on the MOSFET, then the TV should work.
Right now you have at least two problem, one the MOSFET U33 is not being turned on, two the BL-ON is not present.

I tested the connections suggested using 470 ohm resistors to feed the three pins as stated. With the system not connected, as stated, there is no power from the supply except the 5 ST. There is also no 12v from the supply either and there is only 100vdc on the 160Mf cap on the power board.

When the system board is connected with all connections restored as normal, the high voltage DC used to power the chopper on the power board returns to 385vdc. Something is causing the power supply to shut down if disconnected from the supply. I am not aware of any supervisory or shutdown from the system board if not connection but there must be.

Can you please assist as to why this is occurring. Someone with your experience and familiarity with these sets would likely understand the issue without a schematic in hand. I did manage to find another power board on ebay the seller claimed was good, and having no previous repairs, after a detailed inspecting I saw no reason to doubt the seller and installed it. There was no change in the original symptoms of no audio or back light.

Your input would be so much appreciated, as I feel I must have over-looked something critical.

Thanks so much!!
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Old 04-18-2018, 01:42 PM   #51
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Default Re: Need schematic for Visio LC420

It sounds like you are not getting the connection between PS-ON pin and the 5VSTBY pin to simulate the the PS-ON signal, we know that the PS-ON is being sent by the main board when the cable is in place so all we doing is to simulate the PS-ON signal using the resistor. Please recheck your work.

"and there is only 100vdc on the 160Mf cap on the power board." That must be an error because that cap get it Voltage from the bridge rectifier (as you can see how it is connected on the bottom side of the board) the minute you plug the power cord into the AC outlet, it should show around 165VDC right between the two legs.
BTW, did you count the pins of connector CN201 correctly? Can we see the pictures as how you have those 3 resistors connected?

Vizio 0500-0407-1030 Power Supply/Backlight Inverter E3D420VX E420VL E420VO
http://www.shopjimmy.com/vizio-0500-...pply-unit.htm#
Pictures provided by shopjimmy.
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File Type: jpg shopjimmy-0500-0407-1030-bottom_4.jpg (1.30 MB, 0 views)
File Type: jpg shopjimmy-0500-0407-1030-top_4.jpg (1.44 MB, 2 views)

Last edited by budm; 04-18-2018 at 01:49 PM..
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Old 04-18-2018, 02:15 PM   #52
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by budm View Post
You can test the power supply/inverter backlights by itself (the cable between the main board and the power supply board MUST be disconnected first) using three 470~1K resistors between 5VSTBY and PS-ON pin, 5VSTBY and I-ON/OFF (BL-ON) pin, 5VSTBY and DIM pin.
Budm,

I think i misunderstood your instructions above simple as they are. There are four isolation resistors required for this test since there are 4 forced line to the 5vSB rail.

This time I did not leave out PSON which I had previously and all voltages appear normal except the PSON voltage which was 3.9vdc compared to the other leads all at the 5v SB rail. Still no BL on screen.
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Old 04-18-2018, 02:43 PM   #53
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by budm View Post
It sounds like you are not getting the connection between PS-ON pin and the 5VSTBY pin to simulate the the PS-ON signal, we know that the PS-ON is being sent by the main board when the cable is in place so all we doing is to simulate the PS-ON signal using the resistor. Please recheck your work.

"and there is only 100vdc on the 160Mf cap on the power board." That must be an error because that cap get it Voltage from the bridge rectifier (as you can see how it is connected on the bottom side of the board) the minute you plug the power cord into the AC outlet, it should show around 165VDC right between the two legs.
BTW, did you count the pins of connector CN201 correctly? Can we see the pictures as how you have those 3 resistors connected?

Vizio 0500-0407-1030 Power Supply/Backlight Inverter E3D420VX E420VL E420VO
http://www.shopjimmy.com/vizio-0500-...pply-unit.htm#
Pictures provided by shopjimmy.
The 5vsb from the power board is cut so as not to feed the system board and where there are (4) 470 ohm resistors each connected via jumper from the four pins you specified and as just reported have the correct voltages but still no BL. Again the PSON lead is being pulled to 3.9VDC by the power board but the HV DC on the main cap has returned to 335vdc. I am using the other power supply I purchased. I cannot use my original supply since removing a switching diode marked A6, a MOSFET marked RNW03 (I think its a MOSFET) for measuring and managed to accidentally discard them for bad components I intend to replace these as soon as someone can identify a replacement I can get from Mouser or Digikey. Hopefully you can help me identify these so that I might determine if my power board was indeed the cause but so far, it does not seem that way.

Thanks
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File Type: jpg IMG_4738.JPG (917.6 KB, 2 views)
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Old 04-18-2018, 04:27 PM   #54
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Default Re: Need schematic for Visio LC420

You have to remove the cable that go the main board so it has no connection to the power supply board, we are tying to test power supply board as a stand alone.
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Old 04-18-2018, 04:28 PM   #55
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Default Re: Need schematic for Visio LC420

Quote:
Originally Posted by jkb242 View Post
The 5vsb from the power board is cut so as not to feed the system board and where there are (4) 470 ohm resistors each connected via jumper from the four pins you specified and as just reported have the correct voltages but still no BL. Again the PSON lead is being pulled to 3.9VDC by the power board but the HV DC on the main cap has returned to 335vdc. I am using the other power supply I purchased. I cannot use my original supply since removing a switching diode marked A6, a MOSFET marked RNW03 (I think its a MOSFET) for measuring and managed to accidentally discard them for bad components I intend to replace these as soon as someone can identify a replacement I can get from Mouser or Digikey. Hopefully you can help me identify these so that I might determine if my power board was indeed the cause but so far, it does not seem that way.

Thanks
You have to remove the cable that go the main board so it has no connection to the power supply board, we are tying to test power supply board as a stand alone.
The boosted Voltage on that cap should be in the 380 ~400 VDC range, 335VDC is too low.
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Old 04-19-2018, 08:29 AM   #56
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Default Re: Need schematic for Visio LC420

I noticed that the last couple of replys were not showing up when I logged in to this forum using my PC.

UPDATE

I was improperly metering the 160uf C804 cap when reporting its voltage. I was referencing chassis ground on the secondary side not the primary side which is ~53v above the secondary ground. The true voltage is 390vdc as you stated.

Wanted to measure the BL voltage using a voltage divider composed of 1meg resistors the drop across each would be within the range of digital multimeter.

Would that at least give me a reference to determine if the BL Anode voltage is within range to provide some BL indication. I want to eliminate the power supply with this one test. Then I can proceed to check the lamp circuit for an open or other obvious default. Your thoughts please..

Thanks
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Old 04-19-2018, 09:32 AM   #57
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Default Re: Need schematic for Visio LC420

If the main board is not connected to the power supply board, the BL-ON is present and the CCFL lamps connectors are in place, PS-ON is present, Dim is present then when you plug the AC cord in to the outlet you should then see the backlights come on and stay on if power supply, inverter, and backlights are good, if the backlights flash on for seconds then you may have inverter or lamp/s problem. Ii will only take one bad lamp to cause the inverter to go into shutdown AFTER the good lamps come on.
No need to use resistors on those high Voltage (~2000V high frequency AC), the value has to be correct to draw the minimum current otherwise the protection circuit will also kick in, so watch the panel in dark room to see if the backlights even try to flash on or not.

Last edited by budm; 04-19-2018 at 09:34 AM..
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Old 04-19-2018, 11:09 AM   #58
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Default Re: Need schematic for Visio LC420

Thanks, I will look more closely for a BL momentary illumination.

There is an LED under the power board themat comes on and remains illuminated for about 4 seconds the goes out. What is the purpose of this LED? Could it be a fault indicator?

I was going to see if I could get audio from the sys board just to be sure the receiver is ok. The pins on the cable between the sys board and power supply haven cut for the BL test. Given that, if I complete the 5.0v and 12v connections back to the sys board to check the receiver for audio, this should be fine correct since the other wires have been cut on the sys board to power supply correct?

Thanks
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Old 04-19-2018, 01:33 PM   #59
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Default Re: Need schematic for Visio LC420

So right now the PS-ON wire, BL-ON wire, and the Dim wire are cut and no longer have any connection to the main board for testing the power supply/inverter combo board, correct?
Checking sound will just have to find out because we do not know at this point what else are bad on the main board.
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Old Yesterday, 10:34 AM   #60
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Default Re: Need schematic for Visio LC420

Yes, this is correct.

A bad lamp meaning one that is not ionizing?

This would reduce the overall current drain but it would seem that the resulting drain would only be reduced a fraction of normal drain. Would that cause the protection circuit to act? I think there are 8 lamps, so a reduction in current of
12 1/2%?

Any suggestion to test the lamps individually?

Thanks
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