Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

OK I tried it. Used my bench power supply set to 3.8v to actually get it to read 3.5v at BL_SW. Says it is drawing .05amp and also had the other jumper in place. Plugged in the power but still no backlights. Still getting 22v at vled2. Are we sure BL SW wants 3.3v or should it get more? Should I put more current ?

[R_J]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

What are the Ic numbers on the drive ic's ? You should be safe with +5v. What voltage do you get on VLED1, ILED1 and ILED2?

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

What are the Ic numbers on the drive ic's ? You should be safe with +5v. What voltage do you get on VLED1, ILED1 and ILED2?

they use two the of the same IC and 6 of the same mosfet
vled1 and 2 i get 22v, on iled 1 and 2 i get 0v.
this doesnt change whether or not i have the 3.5v on BL_SW
IC1201
BD9486F
523 H34

IC1101
BD9486F
523 H34

Q1202 AND OTHERS
18T10AGH
52808G

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

Datasheet says pin 2 is the STB pin which turns the ic on or off. It says voltage there can be max 20v. I tried 5.25v and still no change. Kinda not sure of myself here to go higher ...

[R_J]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

Do you have the main board connected? do you have a solid AMP+13V

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

Do you have the main board connected? do you have a solid AMP+13V

the main board still has a short on the amp+13v rail. even after i removed all the components in that area. i posted about it. suspecting an internal short, or maybe it goes somewhere else via some via? no schematic for the board...
its a customers TV and he's willing to purchase the mainboard but we have to be sure the power supply works first, because replacing both boards will not be worth it, sadly for this tv.

i probed the pins on those 2 ics and have readings here. seems we have VCC and STB but not much else going on....
i cant see in the datasheet where it says what STB should actually be other than it cant be over 20...

1 REG50 ----> 4.9v
2 STB ----> 5.5v (im injecting this)
3 OVP ----> 0.7v
4 UVLO ----> 3.6v
5 SS ----> 0
6 PWM ----> 0
7 CP ----> 0
8 ADIM ----> 0
9 RT ---->1.9v
10 FB ---->0
11 ISENSE -->0
12 GND ---->0
13 DIMOUT -->0
14 GATE ---->0
15 CS ---->0
16 VCC ---->12.2

[diif]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

the main board still has a short on the amp+13v rail. even after i removed all the components in that area. i posted about it. suspecting an internal short, or maybe it goes somewhere else via some via?

There is still a diode left on the board in your photo.

[R_J]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

This is a Philips chassis PL15.16, it uses 4 of the BD9486 so it's circuit and voltages could be close.
https://www.electronica-pt.com/esque...ileinfo/36041/
You may need to apply 3~5 volts to the BACKLIGHT-ADJ pin as well but usually it is not necessary to turn on the backlights.
When you monitor the voltage on VLED1 or VLED2, does the voltage spike over 22v for a second when first powered on, or do you get a quick flash of the backlights before it shuts down?

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

This is a Philips chassis PL15.16, it uses 4 of the BD9486 so it's circuit and voltages could be close.
https://www.electronica-pt.com/esque...ileinfo/36041/
You may need to apply 3~5 volts to the BACKLIGHT-ADJ pin as well but usually it is not necessary to turn on the backlights.
When you monitor the voltage on VLED1 or VLED2, does the voltage spike over 22v for a second when first powered on, or do you get a quick flash of the backlights before it shuts down?

No flash at all...I'll check voltage but I doubt it
I don't see adj pin but I'll look harder

[R_J]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

On this board backlight adjust is labeled PWM1 and PWM2 but are driven from the same pin on CN501 pin7?

It looks like cn501
pin3 = Protect
pin5 = BL-SW
pin7 = PWM

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

On this board backlight adjust is labeled PWM1 and PWM2 but are driven from the same pin on CN501 pin7?

It looks like cn501
pin3 = Protect
pin5 = BL-SW
pin7 = PWM

yes this is correct. pin 7 goes via 2 separate traces each through around a ~9k resistor and then to one of the pins (same one no doubt) on either of the IC's
putting 5v to both pin 7 (i soldered a wire to a dot that was connected to that trace) and the BL_SW jumper wire, in addition to jumping P_ON_H2 with the 21V gets the power supply up and running and powering the backlights.
so thank you for educating me on how these style of PSU work...i should be able to diagnose these much faster now! we will be ordering the mainboard. most likely tv will be fixed. ill give an update here when it comes in.
thanks again!

i am still interested in possibly repairing this mainboard, if only to learn more. i guess ill try injecting some voltage and seeing if i can find the short.

[triplefour]

Re: Emerson LF402EM6F NO STANDBY, DEAD SET!!! HOW DO YOU TEST FOR VOLTAGES!!!

late update but the replacement mainboard did as expected, fix the TV. success! but now i have another TV of the same kind that i have tried to do this with and i am getting no voltage on the VLED rails. i will make a new post for it.