Emerson LC401EM3F No power - Please Help

[Caleb]

Re: Emerson LC401EM3F No power - Please Help

Philfree, all the parts you tested appear to be good, I usually focus on the zener diodes on these, as every single one Ive had the pleasure of opening has had failed diodes. Dont forget to check the back of the board for surface mount diodes. Also check all the heatsink mounted mosfets for shorts (usually between all three legs but can be any combo) although typically they blow open the resistors that you checked as ok. Check all the diodes first, especially the ones with a zener designation. let us know what you find.

[philfree]

Re: Emerson LC401EM3F No power - Please Help

Thank you for replying i'll keep testing all the zeners and report,by the way i was expecting to read the actual value of the resistors you've circled but instead got 0 ohm is that still a good reading? and no diodes in back of board only an ic.

[philfree]

Re: Emerson LC401EM3F No power - Please Help

And if it's not too much to ask which mosfets should i check?

[Caleb]

Re: Emerson LC401EM3F No power - Please Help

Depending on your multimeter they may read as zero, they will be very low ohms. You can also check them in diode mode to check voltage drop, they are designed to limit current flow and will have minimal voltage drop. Test everything on a heatsink for shorts, also test all the rectifier diodes. If you find a short lift one side of the diode in question to verify it is faulty, often you will have a short across multiple components with only one fault present. You will have to determine what is faulty. These self resonant power supplies can be a pain.

[philfree]

Re: Emerson LC401EM3F No power - Please Help

Thank you sir,i will do as you said and will keep you posted.Thanks a bunch.

[lnlkustomz2007]

Re: Emerson LC401EM3F No power - Please Help

was there any updates on this board? I am working on it my self
i tested the resistors as well and here are my values out of circuit
R609 1.9 ohms
R669 1.2 ohms
R1201 1.9 ohms

mine started with fuse blowing
I ordered the kit from shop jimmy and now the fuse stays good, i have no voltage on standy by or pretty much anywhere

[Caleb]

Re: Emerson LC401EM3F No power - Please Help

What components have you replaced so far?

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I have the same problem. The power board has no voltage. Replaced all the bad parts and nothing. So I have 1.5 VDC on the main filter cap. The power for the cap looks to be controlled by the Relay RL1201. In order for the main filter cap to have power the relay must be turned on. So then it look like IC1201 controls the relay. All the parts are new expect the Optocouplers which I have not tested and I am not sure how to test. Other than that maybe a bad cap but I have not tested those yet either.

Well for some reason the board started working, I have no idea why. So I will have to find another board with the same issue before I can continue. Must have been a bad ground or something. Maybe a wire was not plugged in right. I am determined to become an expert at fixing these boards. Must have fixed about 25 so far.

[dick_barton]

Re: Emerson LC401EM3F No power - Please Help

All the parts are new expect the Optocouplers which I have not tested and I am not sure how to test. Other than that maybe a bad cap but I have not tested those yet either.

Close switch and meter should read 0V, open switch and meter read 5V. No switch needed could just use a jumper wire.

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

What part on the power board would cause the backlights to flicker? This power board was not working at all so I changed out IC 1702 (TEA1611T) because I found shorts in it. After I changed it the TV turns on but the backlights blink on & off constantly. So I have 2 boards doing this and I need to figure out why. Here are some pictures, not sure if they are clear enough.

[dick_barton]

Re: Emerson LC401EM3F No power - Please Help

Is your PFC voltage stable?

[nomoresonys]

Re: Emerson LC401EM3F No power - Please Help

Fault could be with one of the other boards or the panel, faulty led etc.

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

This TV is my test TV so I know the problem is with the Power Board. I have other boards I use to swap out. I have 3 different type audio boards I use when testing the power boards.

My PFC Voltage is jumping from 339 to 343 but slowly and I am guessing it should be around 370. Changing out the Big cap did not make a difference. I got to see if I got a good board laying around.

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I am only getting 10 volts on the Big Filter cap when in standby mode. This must be the problem. If I am correct I should be getting 160 VDC in standby mode. I have been replacing parts and not yet working. All 3 IC chips are the board are NEW.

[JohnCT]

Re: Emerson LC401EM3F No power - Please Help

I am only getting 10 volts on the Big Filter cap when in standby mode. This must be the problem. If I am correct I should be getting 160 VDC in standby mode. I have been replacing parts and not yet working. All 3 IC chips are the board are NEW.

If the TV has a power relay on it, then there will be no volts at the pfc cap as it will have a standby supply separate from the full run supply. The standby supply will feed the main board which will energize the coil side of the relay to engage B+ to the bridge cap when the power button is pushed.

If it uses a single supply that supplies both the standby and all other secondaries then there will be 160V in standby and 330 to 380 in full run assuming it has a pfc processor (not all do).

John

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

OK, my board does have a relay. I found 2 diodes on the board that when I ohm check them I get a reading in both directions with them removed. Both diodes are SB140. I think this may be the problem. So I found a SB140 on another board and tested it, I did not get a reading in both directions so that assures me those SB140 diodes are bad. On both power boards they are all bad. Time to order some.

[budm]

Re: Emerson LC401EM3F No power - Please Help

SBXXX
https://cdn.badcaps-static.com/pdfs/...220c3b4255.pdf

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I take that back, I am getting a reading in both direction on every SB140 I test. I can't find my good meter, misplaced it somewhere so I am using a Harbor Freight freebie. I will try running voltage through them.

[Shane711]

Re: Emerson LC401EM3F No power - Please Help

I switched out the diodes and gave it a test, no change. The TV still flickers. If I only I knew what part of the board was causing this I might be able to narrow it down faster.

[JohnCT]

Re: Emerson LC401EM3F No power - Please Help

I take that back, I am getting a reading in both direction on every SB140 I test. I can't find my good meter, misplaced it somewhere so I am using a Harbor Freight freebie. I will try running voltage through them.

Doesn't matter what meter you use; those are schottky barrier diodes, and they sometimes read almost short when you measure them. Sometimes leaving the test leads connected and jumping across them temporarily with a clip lead will allow a normal reading.

John