Vizio E470VL backlight shutting down

[Taterbug]

After reading many, many post here and I have narrowed down the problem to one of two possibilities I think. I can get the backlight to light up at the most sometimes for one or two minutes then i would lose the signal going to the power supply board on pin two of the white 14 pin connector. ( pin 2 is lamp ). If I disconnect the high voltage lines going to the lamps then the signal does not go away. I put my meter on the megohm setting and measured from chassis ground to the pins going to the lamps and read open which is good. I then hooked everything back up and the lamps were on for about 30 seconds before shutting down. I have a static bar checker from the days I worked in industrial electronics which is nothing more than a neon lamp in a tester the size of an ink pen. Using the neon light test I noticed that getting close to the blue caps next to the bottom connector that the neon lamp was alot brighter than next to the top three blue caps. I am thinking that the blue HV caps might be breaking down under a load. Would this cause the symptom?? Also I have checked all mosfets on the main and power supply boards and they look good. The caps have no markings on them. I found some on ebay that say they are used in HV sections of alot of LCD tv's. They are 18pf 6KV. Would this be the right value for the Vizio? Power Supply Board part number is 0500-0407-0700. Any help would be appreciated. I was thinking about replacing all the small blue caps ( about the size of an M&M) first if I can verify that this is the right value.

[budm]

Re: Vizio E470VL backlight shutting down

OK, tell me when you turn on the TV, what do you get at PS_ON, I ON-OFF, LAMP, and Dim PIN, and after it goes into shut down.

[Ltank]

Re: Vizio E470VL backlight shutting down

You are loosing the 3.4vdc command from the main board to the power supply?
I had a Vizio that the command was lost due to the smd npn directly coupled transistors.
Board was repaired. Try jumping the BL-on while jumping PS-on. Does the backlight stay on? Current draw should be same on the inverters. If a over current condition happens the power supply would still shut down.

[Taterbug]

Re: Vizio E470VL backlight shutting down

I will try the jumper. When it goes into shutdown I am losing the voltage on pin 2 which is lamp. Before shutdown I am getting 3.2 volts. Do you know which transistors were replaced and which board were these on?

[Taterbug]

Re: Vizio E470VL backlight shutting down

Here is what I found out. When set plays without jumper for just a few seconds I have .15 volts on pin 2. When the backlight shuts off that voltage goes to zero. I jumpered pins 4 and 2 together and it would still shutdown because I would lose voltage on pin 1 (dim)... If I would jumper pins 1,2&3 together where they all read about 2 volts then the set would play and not shut down. This is strange. Do you think the Main board is bad instead of the PS. I checked the voltages on all the smd regulators and they looked good. How about the transistors you were talking about? Haven't really located those yet.
Voltages on PS board Connector CN201 (when it WORKS)
Pin1 dim - 1.99 v
Pin2 lamp - .15 v
Pin3 Inv on - 3.2 v
Pin4 PS on - 2.2 v

Voltages on PS board Connector CN201 (when it Does NOT WORK)
Pin1 dim - 1.99 v
Pin2 lamp - 0.0 v
Pin3 Inv on - 3.2 v
Pin4 PS on - 2.2 v

[Ltank]

Re: Vizio E470VL backlight shutting down

Can you give us a good pic of the cable connector labels of the main board / PS ?
It seems that the back light comes on and stays on when pins are jumperd but there is some confussion in pin numbers in my thinking. The Pic of CN201 is upside down and the jumper next to it is J71 not to be confused with being pin 1 of CN201.
+5VSB are pins 1-3, SGND are pins 4-7, 12V are pins 8-10, PS_on is pin 11,
I on/off is pin12, Lamp is pin 13, and Dim is Pin 14.
With this being the numbering our logic can be on the same page, Unplug TV wait a few minutes for caps to discharge through the PS, use a 500 to 1000 ohm 1/8 or 1/4 watt reisistors (Radio Shack buy 4 or 5) with the cable from the Main Board disconnected. Use one resistor to make each jumper between pins. There will be several jumpers for testing
Jumper from the 5VSB pins 1 or 2 or 3 to pin 11 PS_on. then simultaniously
Jumper from the 5VSB pins 1 or 2 or 3 to pin 12 I on/off
Now plug AC power plug in the wall and and see if the backlight turns on and stays on.
if yes or no, then then we can work from there. I just want to ensure we are on the same page so the correct part can be singled out as good or bad. Parts can get expensive. I hope that I have not offended you.

[Taterbug]

Re: Vizio E470VL backlight shutting down

Ok.. My mistake Looks like I have been reading the numbering backwards on the Connector.
I will jumper using a resistor this time between 5volts and Ps_on and 5Volts and I on/off. Get back with you shortly with the results. Thank you for the help. I will post a better picture also.

[budm]

Re: Vizio E470VL backlight shutting down

"Pin3 Inv on - 3.2 v
Pin4 PS on - 2.2 v

Those are the two pins you need to feed 3v, for power supply and backlights to come on, you need PS_ON, and IVR_ON signal.
But from your report, the main board is sending the the correct signal to the power supply and the inverter circuit, otherwise you will not have those two signal, the dim signal is also correct. i-lamp I believe is the feedback signal to tell if the lamps are on or not.
You also need to verify that the DC voltage in the primary side main filter cap is around 370~400VDC right at the two legs of the cap.

[Taterbug]

Re: Vizio E470VL backlight shutting down

ok here is what happened. I had to put a 1k resistor from 5 volts to pins 12, 13 and 14 in order to get the set to play. It play for about 5 minutes with a great picture. Then there was a loud pop. What happened is I lost the 24 volts on the power supply board. I found out that two of the regulators had shorted. Q 700 and Q708 both K3568 Switching regulators. I have two replacements ready to put in . Do you think that this could have been the problem all along. Could they have possibly been breaking down shutting down the lamps????

[Taterbug]

Re: Vizio E470VL backlight shutting down

I did verify that the cap voltage is 370volts.

[budm]

Re: Vizio E470VL backlight shutting down

"pins 12, 13 and 14" what are those pins? Never mind, you made the correction on the pin numbers.
" Q 700 and Q708" they are more likely to be MOSFETs, where are they located at on the board/ Can I get good clear pictures of top and bottom side of the board? I do not believe there is 24V power supply on this power supply-inverter combo board, the inverter section uses 370~400VDC to run, not 24VDC.

[budm]

Re: Vizio E470VL backlight shutting down

Which one of the power supply board you have?
http://www.shopjimmy.com/catalogsear...q=Vizio+E470VL

[Taterbug]

Re: Vizio E470VL backlight shutting down

They are just switch transistors . When they blew it shorted out my 24 volts. Pins 12, 13 and 14 are on connector CN201 on the power supply board. They are Pin 12 -Inverter On,
Pin 13 - Lamp and Pin 14 Dim.. I was reading those in reverse earlier.
I would lose lamp voltage without the jumpers. I tried the resistors to the Lamp first (Pin 13) and the back light would still shut down. Then I went with a resistor from 5volts to pin 12(Inverter On) ALSO and still the backlight would shut down Then finally I went from 5 volts to pin 14 (dim) and the TV played until it blew the two transistors. I am going to post a picture of the power supply board and the two locations of Q700 and Q 708 that I am going too replace. They have been removed as well as the heat sink flange so you can see where they were at on the board. PS part number is 0500-0407-0700.

[Ltank]

Re: Vizio E470VL backlight shutting down

You say the TV played. Did you mean the backlight came on or you had video. I had mentioned to remove the cable from the Main Board to PS when using the jumpers.
It is not good to jumper PS when the cable to the main board is still connected. Not trying to be a pain. Details are everything. Electronics can be very unforgiving at times.

[Taterbug]

Re: Vizio E470VL backlight shutting down

When I say play backlight was on everything was working like it should. Back to the original problem. I don't understand why without any jumpers that everything works fine for a couple of minutes then I would lose the lamp signal on pin 13. If I removed the HV output cables going to the lamps the lamp signal would NOT go away. That makes me think that something was breaking down in the inverter section. I am going to replace the switching mosfets that blew and see what happens Without the jumpers first.

[Ltank]

Re: Vizio E470VL backlight shutting down

Well at least the problem finally showed itself. Sound good. Replace the Mosfets then connect all cables and see if it works at that point. Good Luck with it.

[budm]

Re: Vizio E470VL backlight shutting down

"When they blew it shorted out my 24 volts" What 24V, there is no 24v power supply on your board.

[Taterbug]

Re: Vizio E470VL backlight shutting down

Sorry I mean 12 volts. I replaced the mosfets but also found R805 was smoked. It was underneath the large heat sink that was a pain to remove. Does anyone know the value of this resistor? It looks like brown/Black/silver/gold/gray/black it has six bands???? 10 ohms maybe????

[Taterbug]

Re: Vizio E470VL backlight shutting down

I did some research and found out it is a fusible resistor.

[budm]

Re: Vizio E470VL backlight shutting down

That means it has shorted components such as MOSFET. The resistor may be for feeding the B+ to the inverter circuit or it is the Source resistor on the Source pin of the MOSFET for monitoring current flowing through the MOSFET. You need to trace out the two legs of the resistor to see whwere they are connected to.