Emerson TV Buzzing-Won't turn on LF391EM4F

[warriorx1x]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Looking for dump for:

Emerson LF391EM4F

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Bad news for Mother Earth! my 3 Emerson tvs- complicated tv set- have all different problems.

I fixed two more LF391EM4F . One tv has 3.3v standby. Mainboard has all voltages present , changed EEprom fix the problem.

Other one has no standby 3.3v, but flex cable from power supply has 3.3v (pin 8 AL+3.3V).
cn3601 pin 8 is 3.5 ohm then Trace to IC3601 AP1117EG-13(+2.5v REG) pin 2 is 0.2 ohm(shorted to MSD8200DS-S1).
Took out processor IC3001 then everything's Okay. Need to order MSD8200DS-S1 .

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

A ESR meter is 1k or 100k HZ signal generator + low Ohm meter
What do you think, If I put a capacitor to filter out the signal from test lids or change to dc voltage, then read out the value of resistance bridge. Thank you.

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

I do have A CapAnalyzer 88A(Paid $180),can I use as a Leakseeker 89 ?

Nope.

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

The best ESR meter for me, is In-circuit capacitor ESR meter made by Creative Electronics, Yes... Made in USA

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

That EDS-88A is a nice tester, better than what I have. I like it. I can't find any for sale, maybe there is a newer version out there. I guess I will have to find a used one.

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

I do have A CapAnalyzer 88A(Paid $180),can I use as a Leakseeker 89 ?

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

@CapLeaker Thanks for all hints but I'm too much of a coward to use external power supply to do an injection (Because of a bad past experience.). It will save a lot of time.

Seems it is a common problems of this kind of TV .

Another victim:

citywidetvtech Emerson LF401EM5

Was making a chirping beeping sound when trying to power on. AMP+13V Line shorted to ground. C3637 just below the black ribbon connector on main board is shorted.

BA4GU5G0201 3 main board.

There are other ways of finding a short on a main board too. Not everyone has a Leakseeker 89

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

@CapLeaker Thanks for all hints but I'm too much of a coward to use external power supply to do an injection (Because of a bad past experience.). It will save a lot of time.

Seems it is a common problems of this kind of TV .

Another victim:

citywidetvtech Emerson LF401EM5

Was making a chirping beeping sound when trying to power on. AMP+13V Line shorted to ground. C3637 just below the black ribbon connector on main board is shorted.

BA4GU5G0201 3 main board.

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

What? That is totally awesome. I got to test that out. Do you know how many TVs will never hit the dump because of this? This is so awesome. I will let everyone know as soon as I get around to it.

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

so I wasn't far off then. congrats! Nice pics btw.

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Good news for your 5 Emerson TVs and Mother Earth! .....Will cost you almost nothing to repair!

After I removed Amp IC and two down-converters IC3605 & IC3604. Mother board still has short. So, I cut two traces of PCB to isolate the problem. found the low resistance 8.4ohm was caused by..................A SMD cap 4.7uf C3637...................I put all the parts back, but omitting the C3637 cap. The Emerson TV works beautifully.


Emerson TV Buzzing-Won't turn on LF391EM4F
[Tech Tips] Simply remove the SMD cap C3637 4.7uf.

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

I took a break on that TV but I plan to get back to it. It seems there is a very small component causing all the trouble. I think I am going to do what CapLeaker suggested in post #8 and that was to put power to it and see what part warms up and that may be the bad part.

[capwizard]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

@Shane711
What's the resistance between AMP+13v* to GND**?
Mine is about 8.4 Ohm(not dead-short),after removed Amp IC and two down converters IC*** still the same... 8.4Ohm! Is there any luck?

* CN3602 pin 6,7,8,9.
**CN3602 pin 10,11,12,13,14,15.
***IC3605 & IC3604

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Did you follow the 21V from page 52 back to page 48? IC3201 and Q3282 (this one may not be installed)? All around these IC's that are on the 21V line there are chip caps to GND that could fail, zener diodes, other transistors...

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Is there a way to test a voltage regulator when it is removed from the board?

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

There is no longer a short on the board. I found a bridged solder joint and fixed it.

Take the IC off? How about taking them all off because that is just what I did and with NO results.

Well when I blocked off pins 1, 2 ,3, & 4. I believe these are the 12v. The buzzing stopped so it is on that line somewhere.

I removed 1 IC at a time and tested the board. I did Not replace any ICs, I just left them off. IC3604, IC3605, IC3603, & IC3006 EEPROM. No change. Then I decided to remove the audio IC3801 but no change. So I thought it has got to be the main IC3001 MSD8200DS-S1 but no, it was not. Now I have all the major ICs removed and the buzzing is still there. Really? Like are you serious? So now I am thinking is is something so simple and I do believe it is worth it to remove every single component on this board to find out which one is bad because I will know and everyone else will know how to fix this problem.

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

No luck so far. Changed all the caps and didn't make a difference. I have ordered some RT8293AL and the main IC MSD8200DS-S1. Coming from China so it will be 2 to 3 weeks. I am determined to figure this out because so many of these boards are going bad. I can fix it, yes?
I currently have 5 bad main boards with the same problem

I will post all my progress as I come along.

Holy crap... 5 boards doing the same thing? Geez...
Well I hope you figure it out...
Now since you have a few of them bad ones doing the same thing, take that IC off we talked about earlier and see if that short clears.

[Shane711]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

No luck so far. Changed all the caps and didn't make a difference. I have ordered some RT8293AL and the main IC MSD8200DS-S1. Coming from China so it will be 2 to 3 weeks. I am determined to figure this out because so many of these boards are going bad. I can fix it, yes?
I currently have 5 bad main boards with the same problem

I will post all my progress as I come along.

[CapLeaker]

Re: Emerson TV Buzzing-Won't turn on LF391EM4F

Do the same thing to all the voltage rails one by one, so we can try to isolate the problem. You also can try to identify and compare what resistance you get between a voltage rail and GND and compare that to the good main board. BTW: you were right with pin 16.