Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

[Shane711]

Hello Everyone. Of all the TVs I have fixed so far this TV seems to be the hardest. I have come to realize that a diode does not always short out when it is bad, you learn that after blowing a dozen fuses and other parts.

So I have 2 of these TVs, Emerson LC320EM3FA. I have 4 power boards and I only got 3 working. 1 board was easy, all I did was replace the obvious parts and it worked. 2 other board were a challenge and I am not sure what I did to get them working, they just started working after several attempts. There is no short found on the board but as soon as I plug it in the fuse, mosfet, and diodes blow.

This last board I will need the diagram from the service manual to fix it because I have found 2 bad SMD diodes on the underside and I can not identify them. D604A and D1704A. D604A has like a logo mark and the number 27. D1704A I can't see anything on any of my 4 boards.

Does any have the diagram for the power board? BA1AFGF0102 2A1AFN022

These boards have been a challenge and I have to figure out what mistakes I am making so that I can over come this learning curve.

[CapLeaker]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

before you go waaay out of your way, if a part measures bad in circuit, take it out, or lift one side up and measure again both ways to confirm it is shorted.

D1704 (last pic) has 2 diodes in parallel for example. You could also remove these two little SMD diodes and put in a bigger through hole mounted one instead. The provision is there.

Found a service manual for LC320EM2, which should be almost identical to your unit and they show those two D1704 diodes as one 1SS133 high speed switching diode.
The other one I didn't look at yet.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

I know D1704A is bad because it is literally cracked in half But I did not show you a picture of that because I took a picture of a good board. Also I did remove D604A from the board and it was shorted, seeing the 27 on it I was hoping it was a 27V Zener so I stuck one on there. I have no idea if it is correct.

Last night I lifted all of the 6 Rectifying Diodes and tested the board again, the fuse blew so I narrowed my problem down to a smaller area. I may find the problem next time I take a crack at it.

The service manual you provided does not seem to have the power board, the one is shows is too different from the ones I have.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

I would like to figure out these boards and understand them completely to that I can modify them to be better. For some reason there very sensitive and blow quite frequently. Somewhere on the board is a bad design that needs to be corrected.

[CapLeaker]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

o.k. it doesn't show that on your pictures. Please next time only straight shot ones. I checked your PSU on SJ. There aren't 2 diodes in parallel (kinda what it shouws on your pic. One is a 0 ohm resistor (jumper), the other a diode.

27 V zener sounds about right for the other diode.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

The resistor next to diode 1704A is a 100ohm resistor marked 101. I think I got a good picture of Diode 1704A but I have no idea what the marking means. It seams to be a "1" or an "A"

Every one of my boards has the same resistor marked 101. I saw the picture you were referring to on Shopjimmy and it says 101, not 0. I thought it said 0 too until I looked closer and the numbers are so close to each other that it makes it look that way. But it is for sure 101. If it was a zero it would make no sense to have a diode there.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

OK, I think that diode may be a BA277. If the marking is a "1" that may indicate it is a BA277 Band-switching diode

[CapLeaker]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

I was wondering about that it shouldn't be 0, but I am pretty sure that's what I saw, but I couldn't see it any better. Anyhow that diode is easily fixed. So if you take that diode out, you should be measuring that resistor again and verify for it to be within tolerance.

[CapLeaker]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

OK, I think that diode may be a BA277. If the marking is a "1" that may indicate it is a BA277 Band-switching diode

You know there is a huge difference between the 1SS133 in the schematic and the BA277.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

Yes, even I looked at the picture and I see 0. If I look at my board with a magnifier I still see 0 but if I put my googles on which magnifies it 3 times I see 101. And the picture I took was with my USB Microscope. So I am guessing your glasses were smudged, LOL.

What schematic? I have no schematic for this board. And the service manual you provided does not have my board. The marking on the top is a "1" and according to what I read online it means it is a BA277 diode. I just ordered 5 pieces from China.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

After looking more closely at diode D604A I see a "1" so it seems to be "1.27" Or something else. so hard to see things this small. I got a picture with the microscope and it does not seem to be a "1", more like a manufacture code. I can not make it from the picture but this is the best picture I can get.

[budm]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

That MOSFET Gate discharge Diode D1704A will be damaged if the MOSFET went bad and dumped the High Voltage from the Drain pin to the Gate pin and through the RESISTOR/DIODE network and through the output Gate drive pin of the IC to GND. So you may have bad driver IC as well as the MOSFET, You should also check D7105 and all other parts in that section of the circuit.

[CapLeaker]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

Yes, even I looked at the picture and I see 0. If I look at my board with a magnifier I still see 0 but if I put my googles on which magnifies it 3 times I see 101. And the picture I took was with my USB Microscope. So I am guessing your glasses were smudged, LOL.

What schematic? I have no schematic for this board. And the service manual you provided does not have my board. The marking on the top is a "1" and according to what I read online it means it is a BA277 diode. I just ordered 5 pieces from China.

The service manual from my post #2 has a schematic that is similar too yours. It wont totally match, but Funai doesn't totally redesign circuits. So match your circuit to that in the schematic and you find a lot of similarities. Even so it would be nice having a matching schematic, this will do just fine.
And to me that is a 27V zener from you last post #11.

[Shane711]

Re: Emerson LC320EM3FA Power Board Problems BA1AFGF0102 2

That schematic is not similar. If you look at my board the rectifying diodes are very different and on my board the lamp transformers are slanted. Looking at the schematic it is not even close to what I have. It is way too different and it has very few similarities.

Do you know about www.repairworld.com, I have thought about joining it and maybe they will have the service manuals I can not find. Someone told me it cost $50 a year but I just looked and it is $100 a year, not sure what I would get out of it.