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Crafty42

New Member
Ok, well, I've always been one to find answers online, and this is the first time I've needed this type of help, but here we go. I have a degree in Mech Eng, so I have a LITTLE Elec Eng experience...ok, I took one Intro to EE class, and admit I don't know a whole lot about electronics, except you shouldn't get them wet. Well, maybe a bit more than that. My parents have a Sylvania LCD Model 6620LCT TV that quit working. Me, being inquisitive, took it apart and found a 4 amp fuse was blown. My dad ran out to check NAPA for a new fuse and came home with a 2 amp one. We tried it anyway, and of course, it blew. Now, rememeber, I'm not the best with electronics, but I like fixing things. My dad suggests we use some aluminum foil to complete the circuit and see if it works at least, and then we can get a good fuse later. I was leary, but we tried it and that proceeded to blow something that then created a smoke cloud. I don't know what the part is, but I contacted sylvania and they sent me to someone who sent me the service manual that lists the parts. Sorry, this is getting long.... I used the part numbers printed on the main circuit board to cross reference the parts list and found it to be a "LINE FILTER 5.0MH 6Y075" At least I hope. I ordered one off funai for $4.35, which seems reasonable enough if I can fix the TV.

Now since I don't really know what I'm doing, before I go and resolder a line filter in and replace the fuse to just blow both again...is there anything else I can check or do? If that doesn't work, how can I diagnose the problem myself? I'll try to provide any photos or information needed.

Thanks in advance...if nothing, I'm hoping to learn a bit. :)
 

Sceadwian

Banned
You let the smoke out already you can never put it back in =P If you're DAMN lucky the component you actually observed smoking is the only one that failed, replacing it could possible fix the TV, if not... It become problematic at best to identify the problem.
 

mneary

New Member
I'll bet that the line filter acted as a backup fuse.

In most electronics, a fuse is too slow to protect electronic components.

If you're lucky they prevent fires.
 

HiTech

Well-Known Member
I'd tend to think the problem lies further down line in the circuitry and yes, the line filter may have acted as a secondary fuse although the guage of wire typically used is fairly stout, to act as a fuse.
My best adviceto you is this: KEEP YOUR FATHER AWAY FROM ELECTRONICS & ELECTRICITY !! His suggestions are unorthodox and dangerous. As much as your curiosity and desire to repair the television is, I'm sure you've heard the saying curiosity killed the cat and in this situation, satisfaction won't necessarily bring it back! Being a ME yourself, you should be well aware of pneumatic and hydraulic pressures and what kind of damages high level can do. Now, you are dealing with high electrical pressure and the damage effects from that can be further component failures and electrical shock to you.
 

fordo

New Member
Crafty,

If you don't mind spending the money on a technician, I too agree, that should be plan A.

However, if you're just going to junk the tv, I'd say go ahead and replace the filter and fuse (make sure it's the fuse type that Sylvania recommends, fuses have other properties besides current ratings) and see what what happens. If the fuse blows again then it's pretty much down to troubleshooting. At that point, if it were me, I'd need a DVM and a schematic of the tv to try and isolate the problem circuit... I'm not a tv tech, but if you have no picture and no sound I'm thinking that if the fuse that's blowing is the "line" fuse (for the 120 volts that supplies the tv's power) the first place I'd look would be at the power supply(s) in the tv. Again schematics and a DVM go a long way here. Did the service manual include schematics? How about a troubleshooting guide or chart?
 

sheldonstv

New Member
it is very obvious you have not got the necessary skills in servicing this sort of electronic equipment safely.....my advice is put the set back together and have a qualified electronics service engineer repair it for you-switch mode power supplies are not very forgiving if incorrectly repaired you will scrap the set completely if it isn't properly serviced by a competent person with the necessary test equipment and skills-fuse replacement with tin foil just isn't safe practice..........
 
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Crafty42

New Member
Thanks all. Well, I got the new line filter in, soldered it in (though not very well) and replaced the fuse with an identical fuse from the one taken out. 4A 125V. Now, I plugged it in and get nothing at all. No fuse blowing, no smoking line filter... All I can assume is that I soldered the new line fuse in wrong and that's why I get nothing. I used a multimeter to check that I'm getting votage in where the plug solders onto the board, but when I try at the fuse, I get nothing... I don't know if I can get a schematic or not. What is a DVM? Anyway, I contacted one place, they want $ to troubleshoot it, and really, it's just a cheap TV, so I'm more apt to use it as a learning experience and junk it. My other thought is to just replace the main board.....but on the other hand, I could end up spending more money on trying various things than it would to just pay someone to troubleshoot it.

Mom says she think a few lightning strikes caused the failure, and although hoooked up to a surge protector, she believes enough strikes to the house caused it to go. Maybe if we'd replaced the fuse correctly the first time, we'd be good to go, but now I'm at a lose as to what it could be. If anyone has ideas, feel free to let me know. I'll see what I can find... actually, just looked and the second file they sent has schematics. Have at it! :)
 

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Crafty42

New Member
it is very obvious you have not got the necessary skills in servicing this sort of electronic equipment safely.....my advice is put the set back together and have a qualified electronics service engineer repair it for you-switch mode power supplies are not very forgiving if incorrectly repaired you will scrap the set completely if it isn't properly serviced by a competent person with the necessary test equipment and skills-fuse replacement with tin foil just isn't safe practice..........

Thanks Sheldon...While you are right, i don't have the "skills" to know what I'm doing, with some help, I have the skills to get it done on my own. As I just said, It's a cheap set, and I'm willing to risk scrapping it to learn on my own. Thanks for the advice though...if it were my 46" LCD, then I'd definitely not be taking it apart. :)
 

kchriste

New Member
Forum Supporter
By using a "foil fuse", you have most likely driven the final nail into the TV's coffin. You have probably burnt the traces on the PCB or damaged additional components beyond the original fault. Looking at the schematic on page 32 (Main 5/5 Schematic Diagram), you can see the warnings about the fuse at the top of the page. It would have been easy to find a shorted component on the input side of the power supply due to it's simple design.
Do you have an ohm meter and do you know how to use it?
 

mneary

New Member
Since you are a novice, you should be reminded that the of the power supply is live with 170 volts or more whenever it's connected to the AC mains.

After unplugging it, make sure that C610 and C611 are discharged before touching anything.
 

Crafty42

New Member
kchriste, I know using the foil fuse was a bad idea, but how do I tell Dad he's not too bright? It's hard not to trust your own father when they recommend something, even if you know it's wrong. Anyway, yes, I have a multimeter that can read resistance as well. I am fairly handy with it, using them was one of the few things I recall from my intro to EE class.

mneary, I know enough not to mess around with it while it's plugged in, and I'd normally hit the power button after unplugging to discharge any capacitors, but hitting the power button yesterday was doing nothing, so I question if it will discharge them or not. Thanks for the warning and thinking of my safety, I'll be careful.
 

HiTech

Well-Known Member
You don't need to tell your father anything - just have him read this thread! We've already done the talking for you.
 

sheldonstv

New Member
you should have an isolation transformer for running the set while fault finding-first check with your meter what voltage is present(set to read volts dc) across c610,c611- if present switch off and discharge c610 and c611-remove resistors r603,r604,r605,r609 and set your meter to resistance and check the value of them (390k)
if on test you have no voltage present across c610 c611 r601(1.2 ohms ) may be oc due to a sc chopper transistor(q601) any way that is enough for now so tell me what voltages you have after you have powered up the set. also your readings voltage wise should be made with reference to the primary powersupply ground (connect your black meter lead to c610 negative connection)
let me know how you get on then ill talk you through a few basic tests
 

Crafty42

New Member
you should have an isolation transformer for running the set while fault finding-first check with your meter what voltage is present(set to read volts dc) across c610,c611- if present switch off and discharge c610 and c611-remove resistors r603,r604,r605,r609 and set your meter to resistance and check the value of them (390k)
if on test you have no voltage present across c610 c611 r601(1.2 ohms ) may be oc due to a sc chopper transistor(q601) any way that is enough for now so tell me what voltages you have after you have powered up the set. also your readings voltage wise should be made with reference to the primary powersupply ground (connect your black meter lead to c610 negative connection)
let me know how you get on then ill talk you through a few basic tests

Ok, that's a little over my head. I don't have an isolation transformer, and I'm a little confused on why I'd be setting it to read DC voltage. As far as I know, and isolation transformer puts out AC as well. This may be getting too complicated if I have to remove the resistors to test them, and then would need to re-solder them back in. I'm not too handy with the soldering iron. Is there way to test without the isolation transformer and removing things? I did check the voltage while plugged in, and I'm getting 120VAC up to the hot end of the line filter, but when I tried the other side, it was only reading about 1 VAC on the other side. I also tried checking C610 and 611, and was getting a reading of about 1VAC there. I'm not getting any reading across the resistors you mentioned. I tried R620 as well and got a reading of 150...
 

mneary

New Member
Broken into sentences, and re-ordered into the sequence you would perform them, it might be easier to understand:

You should have an isolation transformer for running the set while fault finding. [edit] Without isolation, all points in the circuit are "hot", including "supply ground". They are up to 170V relative to earth. [\edit]

Your
voltage readings should be made with reference to the primary power supply ground (connect your black meter lead to c610 negative connection).

First
set your meter to read volts dc. Check what voltage is present across c610, c611. [edit] It should be between 150 and 175 volts.[\edit]

If a voltage is present on C610, c611, then switch off and discharge c610 and c611. Remove resistors r603,r604,r605,r609 and set your meter to resistance and check the value of them (390k).
[edit] It is only necessary to lift one end of R603.[\edit]

If on test you have no voltage present across c610 c611 then r601 (1.2 ohms ) may be open circuit due to a short circuit chopper transistor(q601).

Any way that is enough for now so tell me what voltages you have after you have powered up the set.
let me know how you get on then ill talk you through a few basic tests
 
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Crafty42

New Member
Ok, well, I tried most of that, except the VDC across the capacitors. I guess they are DC since the store up voltages like a battery. That makes sense, but see my previous post about removing the resistors and that I found them reading nothing with the set off.
 

mneary

New Member
390k is not a meter range that you use often, and on some meters the range is supplied by a different battery. Does the ohm meter read zero when you touch the probes together?
 

mneary

New Member
With the set off and unplugged, and its switch turned on, measure the following on the X1 ohms scale: See if you can follow this in the schematic.

Hot (narrow blade) of the AC plug to the cathode (the end with the bar) of D605.
Neutral (wide blade) of the AC plug to the cathode of D606.
 
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