Emerson LE220EM3 fuse problem.

[Spork Schivago]

My sisters boyfriend brought me an Emerson LE220EM3 22" tv. He says it's been blowing fuses. I'm having trouble identifying which type of fuse it should take. Does it take a slow blow fuse or a fast acting fuse? He replaced the fuse he said after the original blew and they just kept blowing. I'm thinking maybe it takes slow-blow and he's been using fast acting fuses instead? I know it takes a 4A / 125V and he had an 8A / 125V fuse in there!

I've taken the cover off, the caps on the power supply look good. I haven't checked them with an ESR meter or anything. I figured the fuse would be the first place to start. Get the right fuse in there and then see what happens and go from there.

The service manual says it's an STC4A125V U/CT fuse part number: PAGE20CW3402 but I couldn't find diddly squat on that. Any help would be appreciated. Thank you.

[budm]

Re: Emerson LE220EM3 fuse problem.

8A instead of 4A? You do not have the fuse problem, for it blow 8AMP fuses you have bad shorted out parts in the board some where.

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

yeah, I figured if it was blowing an 8A fuse, regardless of whether it was supposed to be slow blow or not, there was issues somewheres and that maybe by him using that 8A instead of the original 4A, he might of made matters worst. I just wanted to make sure I had the right fuse in there before I started playing around. So, do you think it should be a slow blow one or should it be a fast acting fuse?

[Caleb]

Re: Emerson LE220EM3 fuse problem.

emerson with blown fuse= shorted fets and diodes. shop jimmy repair kit lists
Fuse 1 F601
Resistor 1 R611
Transistors 3 Q501, 601, 602
Diodes 8 D601, 602, 603, 604, 607, 608, 609, 653
Capacitor 1 C605

likely you will have to replace all these at the same time to make it work again

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

I can't seem to find Q601. I found Q501 on the back side and Q602 next to the transformer. All the bigger chips on the back look funny. Like they're sweating or something. This includes Q501, Q1001, D653, D656 and IC1001. The Q501 and Q1001 look like voltage regulators. I guess it's just a package I'm not used to seeing transistors in. Thanks for the help. I did pull R611 and sure enough it's bad.

I can post pictures of the chips that look bad tomorrow. The light isn't the right type in here and it's very difficult seeing anything. I need to find a good type of light bulb for the work room. Something that makes seeing these things easy.

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

I found Q601! Little bugger had a heatsink attached to it. It too looked pretty bad earlier and I thought perhaps it was bad. I'll pull that next I guess and test it.

[Caleb]

Re: Emerson LE220EM3 fuse problem.

Q601 is the fet on the heatsink next to the bad resistor.
uncleaned flux can sometimes look like sweaty parts, and these cheap sets are thrown out the door as cheaply as possible, if it is flux it will clean off with a qtip soaked in rubbing alcohol.

was replying when you replied, glad you found it. If you get more of these funai in the future its pretty much a sure bet if the fuse is blown the fet on the heat sink and most everything connected to driving it is toast.
Another thought while Im at it, r602 next to that fet is likely open as well thanks to the 8amp fuse

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

Although me removing these components seem to be going kind of slow (I keep getting distracted), I removed two components and both tested bad. That resistor (which is 0.68ohm 2 watt, right?) and the FET. I'm assuming that FET is why everything else connected to the FET is probably bad. Do you know why it would of failed? I need to purchase a replacement one and I don't want to put the same one in if it has problems. Can anyone suggest a better replacement? Also, can I use any type of thermal paste? It had some white stuff on the heatsink and the back of it. I only have Artic Silver 5. Would that be fine for the replacement or do I need a special type of thermal paste? Thanks!

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

I have a couple power transistors but after looking at the datasheet of the K5A50D FET, I don't think these are suitable replacements. One is a 20W IRF510 power MOSFET, one is a 90W TIP3055 NPN power transistor and one is a 40W TIP31 NPN power transistor.

[budm]

Re: Emerson LE220EM3 fuse problem.

TIPxxx are transistors, not MOSFET.
Did you also check ALL the rectifier diodes and Zener diodes in the secondary side?

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

Not yet. All I've tested so far was the 0.68 ohm 2W resistor (R611), the FET (Q601) and the transistor (Q602). So far, all of them have been bad, like predicted by Caleb. I thought MOSFETs were transistors. Field Effect Transistors. I haven't learned about transistors yet. I know a little bit but just very very basic. Which diodes are the rectifier ones? Are they the four black ones with the stripes next to the transformer?

[budm]

Re: Emerson LE220EM3 fuse problem.

http://www.shopjimmy.com/magnavox-a2...-led-board.htm

Is this the board you have?

D650, D653 (SMD), D656 (SMD).

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

Yes sir. That's the board I have. I was going in order, I've tested everything up to the diodes. D601 through D604 test good. I haven't tested D607, D608, D609 and D653 or C605 yet. Everything I've tested minus D601 - D604 has been bad.

For the non SMD diodes, like D650, I don't have to completely remove it, right? Just remove one lead from the board and test?

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

I removed just one lead from D650, hooked my DCA 55 meter up to it and it seems to test just fine. Vf (forward voltage) = 0.35V, If (test current) = 5.09mA

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

D653 is bad. Haven't pulled D656 yet but I'm betting that's bad as well. I washed the IC and chips with isopropyl as suggested. They all appear to be melted to some degree or another, minus one of them. One appears to be okay, D1001. D656 looks worst than D653. Q501 fell apart when I removed it. Maybe I should just purchase a new board, what do you think?

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

Okay, so I've tested everything that was suggested and this is what I found that was bad:

R611 - 0.68 Ω, 2 Watt 5%
Q501 - Transistor FET 2SK3498 (T6L1FUNANQ)
Q601 - FET K5A50D
Q602 - Transistor 2SC2120-Y (TE2 F T)
Q653 - Transistor SMD KTC3875S-Y-RTK/P

D653 - Diode SMD Shottky SB3200BR (Can only find throw-hole Axial lead)
D608 - Diode 1ZB36BB (Service Manual says Zenier but it's switching!!!)
D609 - Zener Diode HSS4148TE-E (Service Manual says Switching, but it's Zenier!!!)

I don't understand why in the service manual it shows D608 as a Zener diode but it looks like a normal one and D609 it shows a switching diode but it really looks like a glass Zener diode.

The cap is supposed to be 100 uF but it reads as 90.69 uF with an ESR of 0.53 ohm. This is within 10%, but it's really close. Should I replace that cap as well?

I'm also having trouble finding a lot of these parts. I generally go through Digikey but I've used Mouser before. I can't seem to find some of them at all and others I can find in different packages, like through-hole instead of SMD. Any suggestions?

[Caleb]

Re: Emerson LE220EM3 fuse problem.

The small switching transistors are probably not going to be on digi or mouser,probably stuck going to ebay. The fet you can upgrade to a K5A60D (digi had last time I ordered), I also ended up ordering a higher voltage and amperage schottky as they didnt have them in stock as long as forward voltage is same it will work fine. Caps are cheap replace it while you have it apart for good measure. Look at the board designation as well as the body of the diode to tell which is which, there are glass body zeners.

I think the consensus is the schottky is the first in the chain reaction. When it fails short circuit the fet tries to increase its output to keep the output voltage the same which overheats the junction causing yet another short which then pumps high voltage to the driving transistors and signal diodes and blows open the current limiting resistor before the fuse can give way.

[budm]

Re: Emerson LE220EM3 fuse problem.

"I think the consensus is the schottky is the first in the chain reaction. When it fails short circuit the fet tries to increase its output to keep the output voltage the same which overheats the junction causing yet another short which then pumps high voltage to the driving transistors and signal diodes and blows open the current limiting resistor before the fuse can give way." I cannot say it any better than that, badly designed circuits. I do not even try to fix these two transistor switching circuit.

[Spork Schivago]

Re: Emerson LE220EM3 fuse problem.

Thank you for the reply guys. Maybe I should junk it then? The guy said I could keep it for parts but I decided I'd try to fix it anyway. For the K5A60D, Digikey wants me to order 50 for 63.28$. I don't want to do that. I had looked into that one as well. I had picked these for other replacements but weren't sure if they were good replacements or not:
1N4148-TPMSCT-ND ( http://www.digikey.com/scripts/DkSea...76545492471371 )

MAZ23600AGCT-ND ( http://www.digikey.com/scripts/DkSea...76545492471371 )

P0.68W-2BK-ND ( http://www.digikey.com/scripts/DkSea...76545492471371 )

I'm sure the resistor is fine (the last one). The MAZ23600AGCT-ND is a zener diode, 36v, 1 watt DO41 and the 1N4148-TPMSCT-ND is a general purpose diode, 75v, 150ma DO35. That's all I could find for replacements. I don't even know how to begin looking for a SMD schottky diode on Digikey. I tried earlier but got really confused with the filters. I tried matching stuff up with the service manual, and I want to say I finally found one but it wanted me to order something like a minimum of 3,200 of them.

On the board, there's a glass diode, D609. I thought it was a zener diode because it was glass. However, the service manual shows D609 as a switching diode. There's a black with silver band normal looking diode, D608. I thought that was a normal one, the service manual shows that as the zener diode. The normal looking diode, D608, says 1ZB3BL on it.

[Caleb]

Re: Emerson LE220EM3 fuse problem.

Schottky part number S320FSCT-ND or SK3200B-LTPMSCT-ND
Zener can be 1N4753A-TPTR-ND
resistor is fine P0.68W-2BK-ND
Fets that should be compatible and in stock R5005CNX-ND or ZDX050N50-ND
1n4148 1N4148TACT-ND

The filters on digikey can be a real headache, they often leave you with nothing even though they have it in stock. Be sure to order a couple of each parts, it really sucks to burn a 10 cent part and have to pay 3.50 to ship another. Shop Jimmy had a complete repair kit for about 20$ as well if you need a one stop shop.

Have you checked that large white resistor yet, It is a common failure on these that normally isnt included as they usually survive the first blown fuse but fail on the second attempt.