Vizio E55-F1 dark backlight zones. LED failure or Dimming Zone Driver?

[howardc64]

Problem

Fixing a dimming zone TV with LEDs not lighting up. Dimming zone circuit introduces added variable to diagnose LED and/or Dimming Zone Driver board? Some 1/2 rows of LEDs appears to be out in active dimming zone off AND some brightness flickering with active dimming zone high while playing changing video



Model & Board Pics



Conflicting Spec

Vizio indicate this TV has 10 dimming zones. However, LED strips and Zoned light driver connector suggest 12

https://www.shopjimmy.com/vizio-gj-2...ght-strips-12/



LED Testing



spreadsheet source : https://docs.google.com/spreadsheets...it?usp=sharing

Dimming Zone Board Testing

All FETs read similarly in diode test

Question

Prior to panel disassembly to access LED bar. Likely failure is LED bar or Dimming Zone Driver Board? or even PSU power to the Driver board?

Since dome LED 1/2 rows shows 0.5v moving voltage using LED test, maybe most likely LEDs? And/or Driver Board failure (4V overdrive swing in black video test + dimming enabled) damaged the LED strips?

[Diah]

log in service menu and call white balance the dimming will be disabled and you will be able to approve yours own theory

[howardc64]

This Vizio has Active Full Array control in regular TV menu under MENU->Picture->More Picture. Turned off to check post #1's voltage check summary. Also Turned on to high + stream a youtube black video to check voltage (also in post #1's voltage check summary)



Under service menu (MENU-4210) There is only backlight test but unclear what it does (maybe cycle through all 12 zones? But its very quick and perhaps I have some LED zones out making it unclear what is intended pattern)

service menu did show backlight has over 14k hours.

[howardc64]

Most likely is LEDs

• Tester shows some strips have moving voltages in LED tester indicating variable current
• Adjusting backlight level causes some LED strips to come on or go dark randomly
• 14k hours on the LEDs.

Will replace LEDs and report back.

[howardc64]

Found the problem and its the first time I've seen this one.

• All LED strip test okay at 18.5v applying voltage directly onto the strip + - pads.
• LED tester LED driver board connection shows variable voltage in some strips 19-25v
• LED tester (self adjust voltage seeking target current) with changing voltage is due to changing resistance.
• Found poor contact between LED strip and its connector. Am able to check resistance of this connection and its in many Ks or 1/2 M ohm. If I tin the LED strip contact or solder a jumper. The connection is reliably near 0 ohm. and LED tester reliably drives the LED strip at 18.5v from driver board connector.

Perhaps the zoned backlight and the constantly changing thermal profile worn down this connection?

[howardc64]

UPDATE:

• Jumpered all the + side of all 12 LED strip connector and all resistance across connection is < 1 ohm.
• - side are all < 1 ohm without jumper (will jumper it to be certain) so quite interesting all the failures are on the + side.
• LED tester shows 18.5v on all strips from the LED rail connector.
• Quite a few LED strip securing screws are loose. Backside of strip is double side taped down. Probably also result of high thermal cycling from dynamic dimming.

[EazyBone]

Interested to see what happens.

[howardc64]

Fixed... for now haha. Jumpered +- across all 12 strip connectors.

• Resistance is < 1ohm across all 24 connections.
• LED tester reaches 18.5-18.6v instantly on all 12 strips
• Backlight test in service menu just cycles all 12 strips (see video). Have another Vizio with active dimming and it does the same.
• Also touched up backlight driver connector solder to avoid brittle lead free issue in the future.

Maybe best to turn off Active Dimming? TV does get much brighter with AD on high so people probably prefer that.

[EazyBone]

That's hilarious. Very well done

[howardc64]

BTW, all this is the result of trying to reduce 1 labor step to avoid using human's dexterous fingers to click on a robust male/female connector pair and routing a wiring harness that has been matured for 1/2 century.

I'm involved in DIY Tesla car large battery repairs. Tesla also attempted to eliminate this human step and made a robot ultrasonic bonded voltage sensor monitoring flex + wires. We are now seeing thermal cycling and vibration breakage of the ultrasonic welds. Repair require far more labor than originally saved as Tesla decided to use sealant to glue the battery shut haha. In case anyone is curious.

https://evclinic.eu/2024/10/18/tesla...eel-uncovered/

[Diah]

still it sound to me some one play with service menu setting..... before you.... sohold on.... did you log in service menu... to se the steps setting of Dimming... there are over all Tv in 20 60 90 100 % value

[howardc64]

still it sound to me some one play with service menu setting..... before you.... sohold on.... did you log in service menu... to se the steps setting of Dimming... there are over all Tv in 20 60 90 100 % value

Yes, I see the test pattern steps and have tried them. Always setting back to default 0 (and factory reset sets to 0 as well). Not sure these are dimming settings. When smartcast is running, they do nothing. I don't see any other setting for dimming control in service menu. In regular system menu, I can set active dimming to off low med high and system has a default setting on these depending on picture mode. Factory reset (have done many times) always return these to defaults.

My repair on this backlight was down to just testing resistance across the LED strip connection. ohm test one side of the connector and on the + or - contact on the strip and see changing resistance. Once jumpered or contacts tinned, it returned to 0 ohm.

[Diah]

Yes, I see the test pattern steps and have tried them. Always setting back to default 0 (and factory reset sets to 0 as well). My repair on this backlight was down to just resistance across the LED strip connection. I can ohm test one side of the connector and on the strip and see changing resistance.

are you familiar to work and edit service menu ?

if the syncs R on PSU BL circuit got open or changed value to high could also cause this

can you show the service menu steps value

[howardc64]

Please see attached. I looked at every service menu entry and can't find anything that looks like sync R, PSU BL. Also downloaded E70-C3 service manual with same service menu ( link ) and unfortunately no description of service menu other than software update. If there is a step sequence or hidden menu, let me know. Thanks.



At least 2 different LED backlight designs

For future repairers, there are v7 and v9 LED strips (don't know if more) and are totally different despite matching TV model ( E55-F1 ) version # ( LTMWWUMU ) and most of the LED strip part number code ( GJ-2K18-E55-550-D614 ) except for last version # v7 ( ShopJimmy link ) and v9 ( ShopJimmy link ). Mine is v7 with 12 identical strips with 7 LED each and connects to a center bar which zoned LED driver is connected to. v9 is 6 long and 6 shorter strips (Each long connects to 1 short and short gets the voltage feed (presumable both zones) so probably don't have a vertical center bar LED driver connection. So probably can determine prior to disassembly if center connecting bar exist (v7) or not (v9) with rear panel removed ( see pic in post #1 )

[Diah]

i am lost as you,,, i don't take SJ or any others as references... all they are resale.. the BL socket LED+ will tell you how many channel you have

[howardc64]

i am lost as you,,, i don't take SJ or any others as references... all they are resale.. the BL socket LED+ will tell you how many channel you have

Yes, SJ was misleading on this one. Naturally I try to order LEDs before disassembly to avoid having parts opened and scattered while waiting for parts. Unfortunately encountered a mismatch on this one so alerting future repair efforts.

On dimming zones, E55-F1 Vizio spec also give misleading info (they say 10 zones) but clearly there are 12. I can test 12 independent strips (each one = 1 zone) with LED tester. Fully reassembled TV service menu backlight test shine all 12 zones independently (quickly so need to slow down video in post #8) the BL socket connection looks like this for the v7 strips. All the LED strip + rails are ganged together and all LED strip - are independent.



I guess LED strips v9 must be 6 zones or 12. Have to look at BL socket to determine as you suggest.

Anyway, TV works perfectly right now after jumper for every + - of each strip across the strip connection (since measured variable resistance on some strip's + rails). Jumper reduced all connections to <1 ohms and TV works perfectly after 4-5 hours of testing.

One more note of interest. 14k hours on the backlights according to service menu system info. So this 2018 TV was on 6+ hours daily. LG LEDs are usually shining blue by this number of hours haha.