Vizio M502i-B1 won't turn on

[budwich]

Re: Vizio M502i-B1 won't turn on

OK... thanks for the additional info.

hmmm... Since you have now provided the "history", I am thinking that the "on/off" circuit isn't necessarily the issue especially since there is a "secondary mode" (ie. remote) that doesn't work either. In your investigation "travels", I don't recall seeing any parts replacement yet... which seems rather strange given the "power thumping" that was involved. Either a power board issue or some thing strange at the main board is my thought although your testing appears to indicate some issue with the zener in question... which won't hurt to replace. Doesn't really explain why the remote function doesn't work though. :-(

[budm]

Re: Vizio M502i-B1 won't turn on

Budwich:here is a picture of the on/off circuit board. For starters,the voltage on the two wires from the main circuit to the on/off board is 2.85volts. When the on/off button was depressed, the vintage drops to .3 volts. When the board is disconnected, the resistance on the two pins goes from infinte resistance to 479 ohms when the button is depressed. I suspect the zenor diode is open. I also drew a schematic of the board which I will send next

The terminal 1 of the connector showing 479 Ohms is correct because when the switch is activated then you will have total resistance between pin1 and pin 2 (gnd) of 470 + 10 Ohms = 480 Ohms. The circuit is ACTIVE LOW (OFF = >2VDC, ON =<1V), when the switch is activated it will take the pin 1 to ground through 480 Ohms, the pull-up resistor of the micro controller is probably in 10 K Ohms or higher so the Vdrops on 480 Ohms will be close to 0 Volt. The Zener is for protection of the input of the micro controller IC probably 3.3v or 5V Zener, the circuit will function without it, it is not for regulation of the 2.85V. other push button switches of that TV probably are ACTIVE LOW also.
The problem with ON/OFF is some where else.

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

Thanks budm and budwich for your quick response. I got briefly excited after measuring the open Zener diode on the on/off board, thinking, that perhaps, I was on to something. Well, after reading your responses, it's sounds like the voltages that I measured are in line with "Active low (off =>2 volts DC, on =<1 volt"
Now, I am back to square one, thinking about, how can I can locate the "bl-on"pin and measure the voltage. Does it make any sense, to measure each wire to ground in the connector from the main circuit board to the led driver board (while pushing the remote control power button on) to see if there any changes in order to possibly locate the "bl-on"? If I can't find it, I am considering to go on line and purchasing a main circuit board as my first circuit board replacement. Thanks again for any and all suggestions.

[budwich]

Re: Vizio M502i-B1 won't turn on

another question, have you check the tcon board for any blown fuses? Have you tried the "disconnect a cable at the tcon" test to see if anything happens?

[budwich]

Re: Vizio M502i-B1 won't turn on

further reading / guessing... :-)

ps-on is indicating power supply on / active.

on/off is indicating a "low" which I would take as off, maybe standby.

dim is high indicating full brightness... maybe

however, since on/off is low, maybe this is used as an equivalent to BL-ON being off.

This set appears to have FALD / local dimming which means the TCON plays a role in dimming control. Hence, the earlier question. Anyways, its probably more of a "fake analysis" than "real concrete diagnostic" since there is so little info directly available for the set. I'll now leave you with the "real knowledge guys"... hopefully they will come up with more.

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

I removed the metal covering plate that covers the t-con board and attaches to tv stand. I looked very close for any type of fuse or fuse designation on the t-con circuit board. The board is so tiny and is hard to look at the smd parts even with a magnifying glass. I didn't see any fuse. I also unplugged the two connectors to the t-con board. Then, I energized the TV set, and nothing changed (i.e., no sound or standby light, etc). I took some pictures of the board hoping to review them later thru magnification setting of iPhone. I also, removed the power supply board and checked underneath the power supply board for any noticible cracks, poor solder marks, burnt smd parts. I didn't observe anything unusual.

[budwich]

Re: Vizio M502i-B1 won't turn on

well unplugging both cables at the same time likely won't give you much there after from the panel... try just one at a time. Further, which cables are you unplugging, to the panel from the tcon or to the main control card? There is a fuse on the tcon, look close or use the pictures that were nicely post FOR you... its near the connector.

have you tried any "force sequence" for turning on the back lighting ... some thing like vol up, channel down, while plugging in power (check / search the forum for possible sequences)?

[budm]

Re: Vizio M502i-B1 won't turn on

At this point to mew you do have main board problem, it does send out PS-ON otherwise you will not have 24VDC (19V in your case).
You can also verify if the T-CON board SMD fuse does have 12VDC or not, more likely not, that 12V for the T-CON is fed from main board switched 12V MOSFET that is turned on by the micro controller.

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

Thanks again everyone for your patience. Based on your input, I did locate the fuse (F1) on the t-con board near J101. The fuse Checked good. However, there was no voltage present on the fuse terminals of F1 when the set was plugged in. So, if the 12 volts to the t-con board is controlled by the main circuit board microprocessor, then I also suspect that the main control board is suspect.

[budwich]

Re: Vizio M502i-B1 won't turn on

i am totally confused... where is the 12v you measured in the very first page of this thread... its disappeared????

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

Budwich: I still have 11.58 volts (circuit board states it should be 12 volts) on the connector CN9101 on the power supply board.This connector and associated cable go directly to the main circuit board. On the main circuit board, there are two cables that go to the t-con board. At one of the cables and connector coming into the t-con board from the main circuit board, there is a designation on the t-con board that identifies it as j101. Close to this connector is the t-con fuse designated as F1. I measured conductivity across this fuse and it checked out good. However, when I energized the set and measured potential from the fuse to ground, there was no voltage present. It's my opinion, that the main circuit board sends power to the t-con board. However, nothing was present at the t-con fuse (F1). I hope that clarifies the situation,

[budwich]

Re: Vizio M502i-B1 won't turn on

well that might be true IF you knew for sure where the fuse was in the circuit. You need to trace the 12v on the connector at the power board to the main board to the connector at the tcon to be sure.

[budm]

Re: Vizio M502i-B1 won't turn on

http://assets.shopjimmy.com/media/ca...tk0020-top.jpg
FYI: The 12VDC feeding the main board is fed to the switched MOSFET, the output of the MOSFET is then feeds the fuse on the T-CON board. Q205 on the main board (close to the T-CON connector CN205) looks to be that switched MOSFET. More likely that MOSFET is not being turned right now.

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

I ordered the main circuit board and will report back once i receive and install it.

[Misterfixit]

Re: Vizio M502i-B1 won't turn on

I replaced the main circuit board and the set turned on and everything is working fine again. While I had the back off and the set was working properly, I did put a volt meter on the power supply 24 volt pin out connection to see if anything changed. The voltage remained the same as before (19.6 volts). I also checked one of the electrolytic capacitors on the led driver board. As I recall, originally the voltage across each of them was 19.6 (the original 24 volt supply). With the new main board in and the set working, the voltage on c820 was 25.75 volts. I want to thank Budm,Dskall,dick_Barton, Budwich and all the other members who assisted me during my journey in troubleshooting this tv.

[WarAxe]

Re: Vizio M502i-B1 won't turn on

I just discovered this thread. I am having the EXACT same problem as Misterfixit including all the same troubleshooting results (voltages, etc.).

If replacing the main board is my best shot I'll do it. Looks like they're $100 on eBay.

Dare I say this will be my last Vizio TV?