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

[fharris1977]

Hello. I have an emerson model lf402em6f and it has no standby led and it won't power on. Is it possible that it's the EEPROM because I repaired a set that was plugged in the same (possibly bad) outlet and it needed an EEPROM chip. Also with this set, I don't see a legend or test points to test the boards to see which isn't working properly. Should I just assume it's the power supply since there is no standby led or does anyone have any experience troubleshooting this set, because it isn't like the sets I'm used to repairing. I've included pics of the board layout and closeups of the boards and connections. Any help would be greatly appreciated. Thanks.

[CapLeaker]

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

start with checking the STBY voltage on the PSU. If you don't get that, the main board will not turn on.

EDIT: A bad EEprom will not cause the LED to be off. So either there is no STBY voltage on the PSU or the main IC on the main board is bad.

[fharris1977]

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

Hi. How do you test for any voltages? I don't see a legend or any test points that show what pin to test the standby voltage.

[budm]

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

Some of the jumper wires on the cold side have Voltage labels for them, also look at the bottom side of the board.

[petehall347]

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

check the fuses

[fharris1977]

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

check the fuses

Hi. The fuse was blown on the power supply, so I replaced the fuse and it blew soon as I plugged it up. I did see a red, orange color light from the transformer right as it was blown. I got those fuses from Amazon, so I'm wondering if I got a bad batch. I paid 8 U.S. bucks for 20. It's the little brown square fuses. Same specs. What do you think? Also, could you possibly lead me to what's causing the fuse to blow, so I can repair this board instead of contributing to the landfill. Thanks.

[CapLeaker]

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

Sounds like shortet fet’s on the primary on the PSU.

[triplefour]

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

i wonder what happened to his tv in the end?
i recently came across one of these Emerson LF402EM6F and am also puzzled by it. strange labels...connector that is hard to probe so you have to probe the jumper wires where the labels are.
the symptoms i have are this:
when connected up normally, you can hear a whine coming from the PSU.
no standby light comes on.
no response to power button or remote.
when power supply is alone it is quiet.

i want to make a positive diagnosis whether it is main board or power supply.
leaning towards power supply.

markings on board are strange compared with other brands.
the label P-ON+21V seems like it might be a typo and should say
P-ON+12V
but who knows?
no clue how to "trick the PSU" to turn on without the mainboard.
usually we connect 5v standby to PSON thru a 1k resistor.
but there is no 5v standby that i can find.
there is a label marked
ALL+3.3v which may mean "always on 3.3v" which could be the standby
but it reads -8.02v when mb is disconnected. i can only find that label on the board in one place
and it appears to be connected to what would be a jumper wire but there is no jumper wire there.
this voltage rises to -0.29v when mb is connected.
there is another rail labeled AMP+13V which...again no idea what it is... reads 8.2v alone and 0.95v when mb is connected.

voltages:

label: alone / with MB
ALL+3.3v= -8.02v -> -0.29v
P-ON H2= 0 -> 0.04v
AMP+13V= 8.20v -> 0.95v
Protect3= -0.07-> 0.02v
OVP2= 4.56v-> 4.44v
BL_SW= 0 -> 0.03v
VLED1= 12.45V-> 12.19V
VLED2= 12.45V-> 12.19V
LDR2= 0 -> 0
SOURCE2= 0 -> 0
ILED2= 0 -> 0
CDR1= 0 -> 0
PWM1= 0 -> 0.03v
P-ON+21V= 12.69V -> 12.14V
PFC(big caps)= 167v -> 154v

PFC seems low. not getting boosted. not fully turning on.

seems like P-ON H2 might be the switch to turn the PSU on...should i just inject 5v to it?
and while im at it, to BL_SW as well?

any ideas?

[neilc6]

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

These Philips/Emerson sets have weak power supplies. Few threads here.

https://www.badcaps.net/forum/showthread.php?t=72916

https://www.badcaps.net/forum/showthread.php?t=71919

If the power supply is squealing with the main connected, likely a shorted chip cap on the supply rail on the main.

https://techhometravel.com/philips-4...oesnt-turn-on/

[CapLeaker]

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

Here is a different Emerson TV repair, but it does give you an idea what all could be blown up. Usually all starts with a diode failing in the secondary of the PSU. What are the voltages on the power supply without the main board connected?

https://www.badcaps.net/forum/showth...hlight=emerson

[nomoresonys]

Re: 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!!!

Here is a different Emerson TV repair, but it does give you an idea what all could be blown up. Usually all starts with a diode failing in the secondary of the PSU. What are the voltages on the power supply without the main board connected?

https://www.badcaps.net/forum/showth...hlight=emerson

i listed those voltages in my post. there are 2 columns. one is for PSU alone and one is for when the MB was connected. i will read these other threads. thank you!


...the main thing i see right away is that i do not have the always on 3.3v which i would need to do these 1k jumpers to trick the psu on.
so...why dont i have it?

i mean...its like some crazy negative votage!

[nomoresonys]

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

so all the diodes and resistors on top of the board are ok?

[nomoresonys]

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

maybe try testing those powerboard voltages with mainboard and backlights unhooked if you haven't already, see if theres any difference.

[CapLeaker]

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

i listed those voltages in my post. there are 2 columns. one is for PSU alone and one is for when the MB was connected. i will read these other threads. thank you!


...the main thing i see right away is that i do not have the always on 3.3v which i would need to do these 1k jumpers to trick the psu on.
so...why dont i have it?

i mean...its like some crazy negative votage!

I don't know, why the 3.3V isn't present. Kinda weird seeing that negative voltage there. Are you using proper ground on the secondary for your meter probe? You can't use the same ground for the primary and secondary. If that 3.3V is still weird follow the voltage rail backwards towards the transformer. Why backwards? I just find it easier. In this case the primary has to be semi working. The only thing we don't know is the PFC in the primary. without the PFC, there is no 21V. But you don't have STBY, so fix this first. Measure the 3.3v rail on the main board with it disconnected, see if there is a short or something.
Good luck!

[triplefour]

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

I don’t know, why the 3.3V isn’t present. Kinda weird seeing that negative voltage there. Are you using proper ground on the secondary for your meter probe? You can’t use the same ground for the primary and secondary. If that 3.3V is still weird follow the voltage rail backwards towards the transformer. Why backwards? I just find it easier. In this case the primary has to be semi working. The only thing we don’t know is the PFC in the primary. without the PFC, there is no 21V. But you don’t have STBY, so fix this first. Measure the 3.3v rail on the main board with it disconnected, see if there is a short or something.
Good luck!

i rechecked it and for sure its -8.something volts when just by itself. i am using cold side ground. one of the many jumper wires that say ground, and also i used the area around the screw just to be sure and same reading. i traced it to pin 8 on the connector that goes to the mainboard. well pin 8 depending on which side you count from. there is no indication. anyway i dont see a short on that pin to ground when i test mainboard by itself. i see 560 ohms or so. is that about right?

i will try tracing that 3.3v rail backwards...will post a picture with drawing on it or something.

[triplefour]

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

the "ALL+3.3V" line goes from the connector (pin 8 i say)
to this point where there could have been a jumper. but the jumper is missing. and there are missing components all around
where the jumper would have led to. so it doesnt come from there. or go to there...
the only thing it can come from then is thru the smd resistor marked 912 which is 9100 ohms. it reads fine.
next resistor it goes thru is labeled 333 which is 33000 ohms and that also reads ok

i have attatched a picture that shows tracing and voltages observed. this is of course with psu by itself.

not sure what to make of it.
all the pins on that side of transformer are shorted to ground. that cant be right can it? then where is any of the voltage coming from?

[diif]

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

Are you using the ground marked on the PCB ? you have marked two GND points but i don't think they are correct.

[lotas]

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

That's where GND, (-).

[CapLeaker]

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

Wrong GND. Try this. Didn’t see lotas post, but it’s the same thing.