Emerson LF401EM5 LED TV no power won't turn on

[dskall]

Re: Emerson LF401EM5 LED TV no power won't turn on

Check the temp of the diode you replaced. I am not sure if that is a good replacement. May be what's making the noise.

[dick_barton]

Re: Emerson LF401EM5 LED TV no power won't turn on

The diodes are not replacements for each other so that's your problem.
The SBxxx is a fast acting Schottky rectifying diode and the INxxx is a general purpose diode.

[Toddo]

Re: Emerson LF401EM5 LED TV no power won't turn on

Check the temp of the diode you replaced. I am not sure if that is a good replacement. May be what's making the noise.

The diodes are not replacements for each other so that's your problem.
The SBxxx is a fast acting Schottky rectifying diode and the INxxx is a general purpose diode.

Yikes OK. I don't know where I'm gonna find the SB3A0. Couldn't find it anywhere. Anyone got any info where to find that diode?

Edit: I just wanted to ask one other thing. The three lead component from ShopJimmy (is that a cathode diode or a FET?) is screwed to what looks like a heat sink. That should have some thermal paste between that and the heat sink I'm guessing. It had some white paste behind it on the old one. I figured it was thermal paste. I put a little bit of Arctic Silver between them on the new one.

Edit 2: I just found some good information on diode substitution here - Schottky Diode Substitution

[Toddo]

Schottky SB3A0 Equivalent is SB3100

Looking at the datasheet for the SB3100 here - http://www.futurlec.com/Diodes/SB360.shtml

..it looks like the equivalent of the SB3A0 here - https://store.comet.bg/download-file.php?id=1701

I found the SB3100 on Ebay here shipping from China - http://www.ebay.com/itm/20pcs-SB3100...8AAOSwT5tWL0U8

Now all I gotta do is wait a month and a half for it to ship from China

[budm]

Re: Emerson LF401EM5 LED TV no power won't turn on

BTW, any component that is installed on the heatsink, if it has insulation sheet such as MICA and insulator for the mounting screw, you need to make sure they are back in place or you will short out the new part.

[Toddo]

Re: Emerson LF401EM5 LED TV no power won't turn on

BTW, any component that is installed on the heatsink, if it has insulation sheet such as MICA and insulator for the mounting screw, you need to make sure they are back in place or you will short out the new part.

Thanks for the info. That component on my board didn't have any insulating material between it and the heat sink. Just a whiteish looking paste which I assume is thermal paste.

Question: Do SMD's have polarity? This is one of the ShopJimmy SMD's I soldered on. (Please ignore the atrocious soldering beads. The one on the left looks like a dog pile).

If you see the lines on that SMD, I wasn't sure if that indicated polarity so any SMD's with lines on one end I just took a guess and turned it to the side on the printed board that the arrow is pointing to which looks the most like a line for match up with polarity.

[budm]

Re: Emerson LF401EM5 LED TV no power won't turn on

The white bars are Cathode so you have it on correctly.

[Toddo]

Re: Emerson LF401EM5 LED TV no power won't turn on

Well I finally recieved and installed the Schottky SB3100 diode in place of that general purpose rectifier and still have the screeching sound coming from the yellow transformer. The good news is, this is a common problem, the PSU it appears is actually working fine now after the ShopJimmy repair kit job + Schottky diode at D653, and the whole buzzing sound issue has already been discussed in depth on BadCaps here:

https://www.badcaps.net/forum/showth...F401EM5&page=2

It appears the problem is actually coming from a bad componenet on the main board that's making the yellow transformer on the PSU vibrate. Thanks be to the higher knowledge of other members here, they seem to have isolated the component. It seems to be a capcitor. An SMD cap 4.7uf at C3637 on the main board.

I think I can handle removing the old one and soldering on the new. Member Capwizard says he removed the cap and the TV worked great:

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.

How is it that removing that cap and not replacing it with a new one and the TV still works. I will remove that cap from the mainboard to see what happens but shouldn't I replace it with a new one? ShopJimmy does have a main board repair kit that looks like it contains that specific cap:

http://www.shopjimmy.com/emerson-a4g...r-lf401em5.htm

But hey, if the TV will work without that cap with not even replacing it then I'm good with that.


Update: I went ahead and removed the SMD cap at C3637 on the main board and I still got the screeching coming from the power supply. Since I have no capability to track down the problem I guess my best bet is to get the main board repair kit from ShopJimmy or just get the whole main board.

[Toddo]

Polarity on tiny capcitor

So I ordered the whole mainboard from ShopJimmy because they were out of stock on the main board repair kits and I installed it in the Emerson and the PSU is still squealing. So what I then did, which I should have thought of before I tried a known good main board, I unplugged all connections to the PSU except the power cord and I still get the sound. Which means the fault is on the PSU.

When the set is plugged in but on standby the transformer makes a light whine sound, then when you turn it on and the PSU powers up the mainboard and backlight and the PSU gets a load on it then the loud squealing begins. But you can still tell the problem is on the PSU transformer when it's on standby because of the light whine the transfomer makes without a load on it. So it can't be a fault on the main board.

I'm gonna return the mainboard to ShopJimmy for a refund and I've ordered a PSU. This should be the last fix I hope. Still better way better than chucking the thing in the trash. I'm sure Mother Earth will thank me.

I think I should go ahead and put the tiny smd capcitor back on the mainboard that I took off at C3637. Unless someone thinks it's unnecessary. I can't see any indication of polarity on this tiny capacitor. Does anyone know if this type of SMD cap has polarity?

[attainteddragon]

Re: Emerson LF401EM5 LED TV no power won't turn on

ceramic caps have no polarity, so you are good to put it back in any way you like.

[zape]

Re: Emerson LF401EM5 LED TV no power won't turn on

Hi
I'm trying to fix the same power supply board, p/n BA4G25F0102

The transformer was making loud sound and I identified the shorted zener diode on the +21 rail.
I replaced the zener diode and the new one died and shorted the same way.
Looks like the transformer is producing too much voltage.
What could be the reason for that?
I was not able to find the schematics of this particular board but it appears to be similar to the attached one (see page 39).

Any ideas?

[zape]

Re: Emerson LF401EM5 LED TV no power won't turn on

Fixed it.
Optocoupler was at fault.

[dewds]

Re: Emerson LF401EM5 LED TV no power won't turn on

Did you ever show which parts you replaced?I am unsure where the glass diode goes forgot the names of them sorry lol will come to me once i hit send.

[wichochao]

Re: Emerson LF401EM5 LED TV no power won't turn on

Please someone has a electrical diagram for Emerson LF401EM5 or service manual?

[wichochao]

Re: Emerson LF401EM5 LED TV no power won't turn on

I looking for power supply board, BA4G25F0102 Electrical Diagram anyone can help me?