Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

[DXseekerMO]

Hello everyone, I've had this TV for almost 6 months now, just sitting in the fix-it room and it would be great to get this finished up.

It sounds like the typical Vizio complaint….hit the power button, backlights flash, image on screen but no picture with sound…so what do I do? Order backlights from SJ without taking a single voltage reading. Apparently my “jaundiced eye” over-rode my need to do a diagnostic. This was a mistake.

Install SJ backlights….problem still exists. Check all connections and connectors….no happy. When the backlights flash…they all flash….as if to say “way to go dummy”. Rows 2 and 3 of the LED strips are noticeably dimmer than the others tho.

So how about some voltage readings?

CN201 (to main board)

Pin#.....Function....Volts (tv off)….Volts (tv on)

1...…….+18Vsb...….15.48......……...18.07
2...…...+18Vsb...….15.48.........…..18.07
3...…….+18Vsb...….15.48...………….18.07
4...…….GND
5...…….GND
6......…GND
7...…….PS-ON......…0.........….........3.21
8.........BL on/off.....0.........…………..3.15
9. BoostLEDCkt…… .12............……..3.10 flash, drops to .04
10...…..PWM1...…….0.........…………..2.74 for 3sec, drops to .75, drops to 0
11...…..PWM2........0............………..2.74 for 3sec, drops to 0
12...…..PWM3...…...0...……...………...2.74 for 3 sec, drops to .7, rise 1.66, trails off to 0
13...…..PWM4...…..0............………..2.74 for 3sec, drops to 0
14...…..PWM5...…..0............………..2.74 for 3sec, drops to .75, drops to 0

CN301 (BL connector)

1...…...LED1+...…..31.5...……………..40 to 90.3 to 40.7
2........LED1-...…….0...............…….38.2 to 3.7
3...…...LED2+...…..31.5............…..40 to 89.7 to 40.7
4...…….LED2-...…...0...............…….43.1 to 3.7
5...…...LED3+...…..31.5...…...……….40 to 88 to 40.7
6...…...LED3-...…...12.8............…..15 to 34.6 to 14.9
7...…….LED4+...…..31.5............…..40 to 89 to 40.7
8...…….LED4-...…...12.8...……………..15 to 38.1 to 14.9
9...…….LED5+...…..31.5............…..40 to 88.3 to 40.7
10...…..LED5-...…...12.8............….15 to 38.1 to 14.9

What I see looks like either a PSU with something wrong in the LED boost circuit or a Main Board not outputting the correct PWM value to the PSU.

What do you think guys? Is the PSU or the Main Board the culprit here?

Pictures posted! Thanks everyone!

[R_J]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

The LED supply and Booster circuit is common to all strips. the led- is the line that is controlled. You say rows 2 & 3 are dimmer, but your voltage readings say something different.
LED+ is common to all strips.
led1 & led2 show 3.7 volts, led3, led4, led5 show 15v (I don't understand the 0 and 13v with tv off)
The simple trouble shooting would be to exchange strip led2 with led3. If the voltage changed with the strip, then you know the problem is with the strip.
On the power supply there are 3 (dual fets?) Q301,Q302,Q303. it looks like Q301 controls led5 string only, Q302 controls led3 & led4, Q303 controls led1 & led2
It could be that Q302 or Q303 is bad. swap them around and see if the brightness of the two strips changes to, two other strips.

[budm]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

I am confused about the reading also.
1...…...LED1+...…..31.5...……………..40 to 90.3 to 40.7
2........LED1-...…….0...............…….38.2 to 3.7
3...…...LED2+...…..31.5............…..40 to 89.7 to 40.7
4...…….LED2-...…...0...............…….43.1 to 3.7

For example the LED2 - which is the Cathode return shows higher Voltage that the LED2+ which is the Anode.

[R_J]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

And with the tv power off 0 volts on two return lines and 13v on the three others?

Pin#.....Function....Volts (tv off)….Volts (tv on)
1...…...LED1+...…..31.5...……………..40 to 90.3 to 40.7
2........LED1-...…….0...............…….38.2 to 3.7
3...…...LED2+...…..31.5............…..40 to 89.7 to 40.7
4...…….LED2-...…...0...............…….43.1 to 3.7
5...…...LED3+...…..31.5...…...……….40 to 88 to 40.7
6...…...LED3-...…...12.8............…..15 to 34.6 to 14.9
7...…….LED4+...…..31.5............…..40 to 89 to 40.7
8...…….LED4-...…...12.8...……………..15 to 38.1 to 14.9
9...…….LED5+...…..31.5............…..40 to 88.3 to 40.7
10...…..LED5-...…...12.8............….15 to 38.1 to 14.9

I suspect there could be a an open resistor, shorted diode? that is causing that 0 volts with power off, effecting the two - lines which are likely the two dim strings?
The 13v is likely just a phantom voltage, but it should be there on all 5 lines, so maybe something is shorted inthe current monitoring lines of the two string returns.

[DXseekerMO]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

The LED supply and Booster circuit is common to all strips. the led- is the line that is controlled. You say rows 2 & 3 are dimmer, but your voltage readings say something different.
LED+ is common to all strips.
led1 & led2 show 3.7 volts, led3, led4, led5 show 15v (I don't understand the 0 and 13v with tv off)
The simple trouble shooting would be to exchange strip led2 with led3. If the voltage changed with the strip, then you know the problem is with the strip.
On the power supply there are 3 (dual fets?) Q301,Q302,Q303. it looks like Q301 controls led5 string only, Q302 controls led3 & led4, Q303 controls led1 & led2
It could be that Q302 or Q303 is bad. swap them around and see if the brightness of the two strips changes to, two other strips.

Ok this makes sense. My first impression was a bad diode or FET. Maybe not so much a shorted FET, perhaps non-functional?

I am confused about the reading also.
1...…...LED1+...…..31.5...……………..40 to 90.3 to 40.7
2........LED1-...…….0...............…….38.2 to 3.7
3...…...LED2+...…..31.5............…..40 to 89.7 to 40.7
4...…….LED2-...…...0...............…….43.1 to 3.7

For example the LED2 - which is the Cathode return shows higher Voltage that the LED2+ which is the Anode.

budm, this is read as LED2+ tv off 31.5v, raises to 40v, raises to 89.7v on backlight flash and after flash voltage drops to 40.7. LED2- is 0 volts TV off, raises to 43v on backlight flash and after backlight flash drops to 3.7v. So anode on 2 is higher than cathode.

I could have done a much better job explaining that in the OP.

[DXseekerMO]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

And with the tv power off 0 volts on two return lines and 13v on the three others?

I suspect there could be a an open resistor, shorted diode? that is causing that 0 volts with power off, effecting the two - lines which are likely the two dim strings?
The 13v is likely just a phantom voltage, but it should be there on all 5 lines, so maybe something is shorted inthe current monitoring lines of the two string returns.

I did check the resistors on top of the board and none were short/open, but I didn't spend a lot of time checking that. I will need to re-check and re-confirm. I also checked the diodes on top of the board and don't recall any were shorted or reversing bias...but once again I need to re-check.

The problem is it was 6 months ago I actually installed new backlight strips in that TV resulting in the same symptoms/observations as the ones I replaced. I can't remember if it's the top two rows that are considerably dimmer but I do remember it's two rows side-by-side.

I plan to get back on this TV soon. I got 5 sets of backlights in today. As of now two down, three to go! 2 60"ers and a 65" Vizio home theatre display.

[R_J]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

What about that led1-and led2- 0 and the other led3~5- 12.8. You said that was with power off? If that is the case that might be a clue as to why led1,2- are 0 and not 12.8

[DXseekerMO]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

What about that led1-and led2- 0 and the other led3~5- 12.8. You said that was with power off? If that is the case that might be a clue as to why led1,2- are 0 and not 12.8

As in something open, or inoperative?

[R_J]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

Give me a schematic and I could tell you. I don't know but those circuits are usually the same, so if you do measure 12.8 on the led- on one string, see if you can trace it. then check the one that is 0 volts. there could be an open component not alowing the 12.8 volts to get to the led- or there is something on the led-, killing that voltage. It does seem to be a good clue to where the problem could be.

You also said when the tv turned ON the led1- and led2- went from 38.2 to 3.7. Are you sure that was 38.2 volts or 38.2mV. (is your meter autoranging by chance?) If this IS the case it could be a shorted Q303

What are the numbers on Q301,2,3 and ic300, maybe I can find a similar schematic, The ic looks like it could be a BD9397EFV?
So far I am just using the SJ pictures to figure this out

[DXseekerMO]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

Give me a schematic and I could tell you. I don't know but those circuits are usually the same, so if you do measure 12.8 on the led- on one string, see if you can trace it. then check the one that is 0 volts. there could be an open component not alowing the 12.8 volts to get to the led- or there is something on the led-, killing that voltage. It does seem to be a good clue to where the problem could be.

You also said when the tv turned ON the led1- and led2- went from 38.2 to 3.7. Are you sure that was 38.2 volts or 38.2mV. (is your meter autoranging by chance?) If this IS the case it could be a shorted Q303

What are the numbers on Q301,2,3 and ic300, maybe I can find a similar schematic, The ic looks like it could be a BD9397EFV?
So far I am just using the SJ pictures to figure this out

No definitely 38.2v, not mV

Both LED1 and 2 cathode trace to Q303 which is a PF610HV, as are Q301,2. There is no apparent number on IC300. I checked closely for a number using a magnifying glass and there is no number on it.

[R_J]

Re: Vizio E48-D0 Backlight flash, backlights/connections confirmed good.

Ok so led1- and led2- are connected together at the Q303 mosfet drain, Do the source pins go to ground through seperate resistors?
With the tv off do you still measure 0 volts on the led1,2- ? and 13v on led2,3-?
The ic could have a coating on it, you could try cleaning it with alcohol to read the number. sometimes if you look at it at abit of an angle you can read it better.
Did you check if Q303 is shorted Drain to Source? The two circuits [Q303 (Q309,Q308)] and [Q302 (Q307,Q306)] should be identical