Emerson LC391EM3 stuck in standby

[jrbilodeau]

Hi,

I was recently given an Emerson LC391EM3 that seems to stay stuck in stanby.
When I plug it in I immediately head a click (a relay i think), them the Emerson flashes up on the screen and then there is another click and the TV goes into standby. When the relay initially make the first click their is a red light that flashes on the front, then when it click the second time and goes into standby the red light stays solid.

I read this post (https://www.badcaps.net/forum/showthread.php?t=41495) which seemed to describe the same symptoms, but I'm not sure if it's my inverter board. All of the transformers tested approximately 0 ohms from pin 1-3 and about 500 Ohms from pins 2-4.

I also tried only leaving the Power supply, video board, and circuit where the power button/remote sensor is hooked up and had the same issue. After that i tried also plugging in the cable that goes to the inverter and had the same issue.

With the screen off i also took a look at the ccfl bulbs when i plugged it in and it appears that they all light up, but just briefly.

I don't see any capacitors bulging on the psu and the fuse isn't blown. Any suggestion on how to test the psu? It doesn't seem to list voltages of any of the pins so im not sure what it should be reading.

Here are some images

[selldoor]

Re: Emerson LC391EM3 stuck in standby

Reading this and the other thread I would still query the inverter board/lamps.
The secondary measurement is important about 500ohms is not accurate enough if one
is 492 and one is 508 it could be a problem.
Also are these bulb ends hard wired , fit in metal slots or sit on conductive rubber pads.
If either of the last two you may need to clean up the connectors.

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

Reading this and the other thread I would still query the inverter board/lamps.
The secondary measurement is important about 500ohms is not accurate enough if one
is 492 and one is 508 it could be a problem.
Also are these bulb ends hard wired , fit in metal slots or sit on conductive rubber pads.
If either of the last two you may need to clean up the connectors.

I took all the measurements again tonight and here they are for the transformers from bottom to top.

1 - Pin 1-3 = 0.9 - Pin 2-4 = 486
2 - Pin 1-3 = 1.0 - Pin 2-4 = 496
3 - Pin 1-3 = 1.0 - Pin 2-4 = 495
4 - Pin 1-3 = 1.0 - Pin 2-4 = 493
5 - Pin 1-3 = 1.1 - Pin 2-4 = 494
6 - Pin 1-3 = 0.9 - Pin 2-4 = 497
7 - Pin 1-3 = 1.0 - Pin 2-4 = 497
8 - Pin 1-3 = 1.0 - Pin 2-4 = 494

The ccfl bulbs aren't hard wired. I posted some pics in the 1st post that show that they sit in a white plastic thing. The top is hinged and opens up that the bulb clips in a metal connector. At the other side it look like the bulb slip into a plastic housing and there is a piece of metal that runs across all of the bulb.

The connectors all look really clean. I think the TV was only about a year old and had very little use.

Do you still think i should try and replace the inverter board?

[selldoor]

Re: Emerson LC391EM3 stuck in standby

Well the secondary measurments look ok and if you re happy with the bulb connectors
it is a bit early to rule out other problems. Maybe the main board is not sending a blon signal. Can you find pins on the connectors that say blon dim and on/off ( If just on/off may be power supply on/off depending where it is)
Hopefully others will join in.

[CapLeaker]

Re: Emerson LC391EM3 stuck in standby

Since there is no difference with the inverter board hooked up or not to the power supply, There can be 2 possibilities: Either PSU is bad, or the mainboard is bad. I cannot see any markings on the power supply as pin outs go. Maybe they are printed on the back? If you find them, post them. With the TV on and all wires hooked up, negative on chassis GND, probe all the pins on the plug that goes to the inverter board.

[selldoor]

Re: Emerson LC391EM3 stuck in standby

These Power boards always have a lot of diodes to test! board is also used in Magnavox 50MF412B/F7 and probably others so maybe a schematic somewhere.

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

Ok so i was able to find the service manual for an Emerson LC501EM3 / Magnavox 50MF412b/F7 which uses the same mother board.

I'll take a look at that tonight and see what kind of voltage reading I get.

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

These Power boards always have a lot of diodes to test! board is also used in Magnavox 50MF412B/F7 and probably others so maybe a schematic somewhere.

For the diodes, can these be tested in circuit or do they need to be out of circuit?

[CapLeaker]

Re: Emerson LC391EM3 stuck in standby

if a diode reads short, or weird, lift a leg and test again. Sometimes they read short in circuit, only to find out that there is a low ohm resistor near by.

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

Hey guys, sorry it took me a while to write back, the last few week have been really busy, and i haven't had much free time to work on the TV.

So here is an update of where I'm at. So before creating this thread, i had read about an issue with the same symptoms and same model TV where the issue was the inverter, so i ordered it. Once i found this sight and did a bit more diagnostics (with all of your help) it looked like it actually wasn't the inverter. I tried to cancel the order at shopjimmy.com, but it was too late and return shipping would have cost more then the $13 part.

I figured before spending too much time troubleshooting the PSU I might as well swap the inverter since i had it, but there was no change.

I've started checking out all the diodes and found that the Diode at D703 on the board seems like it might be bad. it isn't shorted, but has a really low ohm reading so i was going to replace it.

I have a question about getting the replacement part. So the Diode had the following # on it SB3A0BL and the manual that i posted above shows the following part # DIODE SCHOTTKY SB3A0BH

I tried looking those part numbers up, but i'm having trouble find datasheets with those numbers. Can someone recommend or possibly link me to a good replacement part for this. I was looking on ebay.ca (i'm in Canada) and some of the results that are showing up have different voltages listed so i'm not sure what to order.

Thanks

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

Any suggestions?

[CapLeaker]

Re: Emerson LC391EM3 stuck in standby

Looking at the circuit my bet for a swap replacement is the schottky SB3100, that should do the trick.

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

I went to my local electronics store today and they said that they don't carry the SB3A0BH or SB3100 or any schottky diodes.

I tried to find a reputable site that sales them but most of the site i found you can only buy them in bulk. I did find some on ebay but they mostly come from china or hong kong and don't even specify the manufacturer.

would anyone be able to suggest a reputable location to buy one of these diodes?

Also some sites listed the SR3100 or MBR3100 as a SB3100 schottky diode...is this right? are they the same?

Thank you

[CapLeaker]

Re: Emerson LC391EM3 stuck in standby

same thing. Did you try Digikey?

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

same thing. Did you try Digikey?

Nope, i didn't see that one. I'll give them a try.
Thanks

[ENGTECHCHRISB]

Re: Emerson LC391EM3 stuck in standby

Does anyone know the link to site to get free service manuals

[jrbilodeau]

Re: Emerson LC391EM3 stuck in standby

Does anyone know the link to site to get free service manuals

I looked quite a long time and couldn't find the exact one for the tv, but i posted one for the 50" emerson a few posts above. it should be pretty similar

[mmartell]

Re: Emerson LC391EM3 stuck in standby

I looked quite a long time and couldn't find the exact one for the tv, but i posted one for the 50" emerson a few posts above. it should be pretty similar

You never said if you replaced the diode and/or if it fixed your tv ??

[hawaiianeye]

Re: Emerson LC391EM3 stuck in standby

yes please follow up!

[ZnsaneRyder]

Re: Emerson LC391EM3 stuck in standby

I want to add to this thread, since this incomplete thread has been helpful in the process of repairing an Emerson LC391EM3.

I downloaded the service manual, which helped me realize an issue with these televisions.

If the TV does not come out of standby, or turns on, then turns off, is because the mainboard is sensing incorrect voltage.

The original mainboard in the TV I am repairing FAILED, and with the NEW main board I get a red standby LED. The 3.3V rail was producing over 5V (in standby) because Q701 (for the 3.3V regulator) failed short, sending the full 12V to the mainboard, frying the mainboard. Once I replaced Q701 the proper 3.3V was present, and now the TV turns on. I have to reassemble the TV.

So YES, that is TWO FRIED BOARDS, but the PSU was repairable.

Don't be so quick to disassemble the TV to get to the backlights/inverter, it is too much risk of damaging the LCD and CCFL bulbs.