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 well what im saying is all those other pins of the transformer are shorted to ground then. and im guessing they shouldnt be!
i am using as ground reference the ground screw, and the jumpers that say ground. im not sure how i could be getting that wrong.

[lotas]

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

ok well what im saying is all those other pins of the transformer are shorted to ground then. and im guessing they shouldnt be!
i am using as ground reference the ground screw, and the jumpers that say ground. im not sure how i could be getting that wrong.

If the middle point (2) is connected to GND, then pins 1 and 3 will show on the multimeter that they are also on GND, as it is not clear here.

[R_J]

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

ok well what im saying is all those other pins of the transformer are shorted to ground then. and im guessing they shouldnt be!
i am using as ground reference the ground screw, and the jumpers that say ground. im not sure how i could be getting that wrong.

You are measuring the DC resistance of the transformer winding, This is normal. According to your voltages that you measured (post#8), the power supply is working and is in standby that is why the voltages are low, this is an always on power supply. and it does not have a PFC circuit, or a 3.3volt circuit.
Check the value of the resistor R669? (post its value) this is the series resistor in the P-ON-H2 line.

Depending on what R669's value is, you should be able to trick the power supply on by using about a 5k resistor between Either the P-On-21 or AMP+13v and the P-ON-H2 line. The P-ON-H2 is the power on line.

When you connect the main board you say the voltages drop to near 0 volts, I suspect you have a short on the main board, likely one of the regulator ic's (ic3201,ic3604) killing the +21v or the audio amp ic. killing the AMP+13V
Disconnect the lvds cable CN3013 going to the panel in case the panel has a short and is killing the voltage

Here is a similar schematic https://www.badcaps.net/forum/attach...5&d=1502380804
Ignore the AL+3.3v circuit, it is not in your power supply. On your tv ALL low voltages 5v, 3.3v etc are produced on the MAIN board from the +21v.

[triplefour]

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

You are measuring the DC resistance of the transformer winding, This is normal. According to your voltages that you measured (post#8), the power supply is working and is in standby that is why the voltages are low, this is an always on power supply. and it does not have a PFC circuit, or a 3.3volt circuit.
Check the value of the resistor R669? (post its value) this is the series resistor in the P-ON-H2 line.

Depending on what R669's value is, you should be able to trick the power supply on by using about a 5k resistor between Either the P-On-21 or AMP+13v and the P-ON-H2 line. The P-ON-H2 is the power on line.

When you connect the main board you say the voltages drop to near 0 volts, I suspect you have a short on the main board, likely one of the regulator ic's (ic3201,ic3604) killing the +21v or the audio amp ic. killing the AMP+13V
Disconnect the lvds cable CN3013 going to the panel in case the panel has a short and is killing the voltage

Here is a similar schematic https://www.badcaps.net/forum/attach...5&d=1502380804
Ignore the AL+3.3v circuit, it is not in your power supply. On your tv ALL low voltages 5v, 3.3v etc are produced on the MAIN board from the +21v.

Thank you for your clarification on this power supply not having the 3.3. I was wondering that myself because I saw that the jumper wire was missing and it had those missing components. I will check those things you said and get back thank you

[triplefour]

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

here are the voltages in that area. i didnt see a R669 but maybe its the R665 that looks like it. that one is in series with P-ON-H2
r665 by the label 103 is a 10k resistor and measures about 9.8k
these measurements were taken with power supply only.

in the other case with the mainboard connected i have only the power supply and mainboard connected in that equation. tcon was not part of it.

[triplefour]

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

so i went looking around those IC's you said to and i noticed one of them had a bunch of shorted caps (appearing shorted anyway) around it.
IC3604 also has 2 pins that are on ground. that may be normal or it may be one of them is shorted?
seems this would definitely be a problem. still need to verify if the PSU doesnt also have a problem tho!

Oh also I noticed that the amp 13v pins on the main board connector are shorted to ground so yes definitely have main board problem.

[nomoresonys]

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

I would remove a cap and recheck it and other 2 for short, if short is still present after removing all 3 caps, the IC is probably bad and causing the short.

[R_J]

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

IC3201 is a MP1472, I think IC3604 is a RT8293AL, if that is the case the shorted caps are on the ic's VIN, this service manual might be close enough

[triplefour]

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

IC3201 is a MP1472, I think IC3604 is a RT8293AL, if that is the case the shorted caps are on the ic's VIN, this service manual might be close enough

thank you i will try that and get back soon with the results

[triplefour]

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

ok so i started removing caps. none of them removed the short. actually its not a dead short from amp+13v to ground, it reads 1.6ohm on my meter which i guess is about 1.2ohm given the resistance of the leads. but anyway that is low enough to make the meter beep in diode/continuity mode so thats why i thought initially the caps are shorted.

anyway i removed all the caps and then eventually the IC as well and i still have that 1.6ohm resistance from amp+13v to ground.

i cant see any other components it goes to but then again...vias....could take things places...
could be an internal short inside the board?

[triplefour]

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

IC3201 is a MP1472, I think IC3604 is a RT8293AL, if that is the case the shorted caps are on the ic's VIN, this service manual might be close enough

i still need to come up with a good way to verify that everything on the power supply is working properly. this pdf is close but not quite the same, as it talks about the all 3.3v but we've established this TV doesnt have that...

[triplefour]

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

Depending on what R669's value is, you should be able to trick the power supply on by using about a 5k resistor between Either the P-On-21 or AMP+13v and the P-ON-H2 line. The P-ON-H2 is the power on line.

can we go back to this? i am unclear here. i couldnt find R669 but i assumed you meant R665 which makes sense. is in line with P-ON-H2 and is 10k.
what does this mean for how i should trick the power supply on?

[R_J]

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

can we go back to this? i am unclear here. i couldnt find R669 but i assumed you meant R665 which makes sense. is in line with P-ON-H2 and is 10k.
what does this mean for how i should trick the power supply on?

I guess it is R665, It is connected to the Q653 transistor base, it looks like 10k so all you need to do is connect the P-ON-H2 line to the P-ON-+21v line, the R665 will limit the current to the transistor so you don't need a extra1k resistor. This should turn on the power supply by turning on Q653 which will cause the collector voltage to go low, changing the reference line to D660 (431) ic which will change the voltage on it's cathode, increasing the voltage across the led in the optocoupler ic601

[CapLeaker]

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

Still a short on one voltage rail? If you have a CC CV bench PSU, back feed some power in into the shorted voltage rail, put 99% IPA on the suspected parts / area and watch what bubbles or what gets hot. That trick saved my but several times and comes in handy when there is a crowded area of parts.

[diif]

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

Did you remove the diode ?

[triplefour]

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

I guess it is R665, It is connected to the Q653 transistor base, it looks like 10k so all you need to do is connect the P-ON-H2 line to the P-ON-+21v line, the R665 will limit the current to the transistor so you don't need a extra1k resistor. This should turn on the power supply by turning on Q653 which will cause the collector voltage to go low, changing the reference line to D660 (431) ic which will change the voltage on it's cathode, increasing the voltage across the led in the optocoupler ic601

OK I connected the the P-ON-H2 line to the P-ON-+21v and the voltages come up as expected. I get the 22 volts and the 13 volts stable. But I am only getting around 23 volts at the Led connectors and testing with my LED tester I see that the strings take around 45 volts to light up. Is there some other thing I need to switch on on the power supply to give full current to the back lights? I don't see a backlight enable pin or anything like that so I'm kind of lost again.

[R_J]

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

The LED's will need to be connected to the power supply, the led drive circuit boosts the voltage from the 23 volts up to 45 volts, but the circuit will fail if there is an open circuit or wrong current draw. The power supply may need to have the 3.3v supplied to the BACKLIGHT-SW to enable the backlights.

[triplefour]

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

The LED's will need to be connected to the power supply, the led drive circuit boosts the voltage from the 23 volts up to 45 volts, but the circuit will fail if there is an open circuit or wrong current draw. The power supply may need to have the 3.3v supplied to the BACKLIGHT-SW to enable the backlights.

ahh i do see a BL_SW on here now... but where can i get the 3.3v from? this board doesnt have it. inject it myself?

[R_J]

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

ahh i do see a BL_SW on here now... but where can i get the 3.3v from? this board doesnt have it. inject it myself?

Normally the main board would supply it. You can use a couple 1.5v batteries in series if you don't have an external power supply, but the backlight led's will need to be connected (and be working) or the circuit will go into protection.

[triplefour]

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

Normally the main board would supply it. You can use a couple 1.5v batteries in series if you don't have an external power supply, but the backlight led's will need to be connected (and be working) or the circuit will go into protection.

i have tested that the backlights are good with my LED tester. i have 3.3v power supply somewhere i can inject with...will do this and get back with result.