AG Neovo F-419

[Mark369]

the board is shuting down after 2 sec. i have full drawing of inverter. can anyone help? had 3 bad caps on c847a, c845, c930. and replaced u920 and u950. t901 and t902 are arcing when put finger near and very hot. to much volts i guss dont know how to test. Drawing for board

[PlainBill]

Re: AG Neovo F-419

the board is shuting down after 2 sec. i have full drawing of inverter. can anyone help? had 3 bad caps on c847a, c845, c930. and replaced u920 and u950. t901 and t902 are arcing when put finger near and very hot. to much volts i guss dont know how to test. Drawing for board

That link isn't working. Looks like a 404 - Server not found.

After you fix the link, good pictures of the top and bottom of the board would be a help.

PlainBill

[Mark369]

Re: AG Neovo F-419

sorry this .one works. I had a guy work on it and just did a bad job. so after 6 weeks I took it back and now i am starting to work on it.

[Mark369]

Re: AG Neovo F-419

Here are the photos of the back.
Sorry cam craped out.[IMG]

[PlainBill]

Re: AG Neovo F-419

Here are the photos of the back.
Sorry cam craped out.[IMG]

OK, that's a start. I still need a picture of the back side of the board.

The schematic of the power supply / inverter is the crudest schematic I've ever seen (other than ones I've drawn, of course). Still with pictures of the back aof the board it should be possible to solve this problem.

PlainBill

[Krankshaft]

Re: AG Neovo F-419

Looks like it's going to be a heavy SMD based design from the top pic.

CCFL shutdown is usually a sign of either an inverter fault or a dead CCFL.

[PlainBill]

Re: AG Neovo F-419

Looks like it's going to be a heavy SMD based design from the top pic.

CCFL shutdown is usually a sign of either an inverter fault or a dead CCFL.

I agree on both points.

Unfortunately, even superpowers won't let us see the other side of the board without a picture. I guess it's time to stop whining. At least he's giving us more information than the 'My monitor isn't working. Tell me what part is bad.' crowd.

PlainBill

[Mark369]

Re: AG Neovo F-419

here are some more photos. i would do all repaires my self with no help if i had to. i think that the transformers are getting too much vots and tuning off ic controler. but dont know how to test.

Thanks for the help.

[PlainBill]

Re: AG Neovo F-419

here are some more photos. i would do all repaires my self with no help if i had to. i think that the transformers are getting too much vots and tuning off ic controler. but dont know how to test.

Thanks for the help.

Sorry, but those pictures aren't good enough. I can't even be sure where the transformer leads are.

Taking good enough pictures is more a matter of technique than equipment. I use a 4 megapixel camera and can get superb pictures of a circuit board when I take my time. And truly horrible ones when I rush.

1. Turn the flash off
2. Work in a well lit room
3. Steady the camera, preferably use a tripod.
4. Some cameras do not focus until the button is pressed. Then it takes a second to actually focus. Press the button slightly, pause while the camera focuses, then press it all the way so the camera takes the picture; release and wait until the entire image is scanned.

I like to be able to follow the traces on the circuit board. I don't have to be able to read the number on an IC, but being able to count the pins is a big help.

PlainBill

[Krankshaft]

Re: AG Neovo F-419

There's alot of heating evident in the area of two driver transistors check those two 4 pin semis.

Grab a datasheet for the pinout.

If it was from ordinary heating then all four of them would have that coloring.

Hopefully when we get some sharp pics I don't eat my words and it's just flux residue.

Be sure to turn macro on the camera as well.

[Mark369]

Re: AG Neovo F-419

i had a guy work on it and replaced the powertrench mofsets but just put a blob of soder over the hole part both sides gate to sorce. trying to desoder

[PlainBill]

Re: AG Neovo F-419

i had a guy work on it and replaced the powertrench mofsets but just put a blob of soder over the hole part both sides gate to sorce. trying to desoder

The easiest way to remove the excess solder is either a commercial product called solder wick (fine copper strands braided together) or just use a piece of very fine stranded wire with a little flux.

The new picture is much better. I've marked it up, measure the resistance between the following points: A - B; B-C; D-E; E-F.

PlainBill

[Krankshaft]

Re: AG Neovo F-419

If those FETs were replaced I'd make sure that no traces were lifted or from the looks of the pics vaporized it looks like the work of a very inexperienced solderer.

Was the monitor working after the replacement of the FETs and then it failed again or the replacement didn't make a difference?

For future reference when using the blob trick (which I use on most 4 pin SMD packages) blob one side put a sewing needle under the first pin melt the blob push the needle through then pull the needle up. If you have fine tweezers they will replace the needle just gently pull one half of the package up. Blob up the other side and remove the IC with pliers or tweezers. Use braid of a solder sucker to clean the residual blobs.

If you're dealing with more than 8 pins Chipquik if the safer option.

[Mark369]

Re: AG Neovo F-419

Thanks Bill the numbers are 21+/-, 15.3, 1.7, 24.7, 15.5 all readings with ohm set to 200k.

Here is a email the guy sent me after 3 months when i found the schematic after i took it back.


Got a soldering iron,
You could check resistance on R922, or R962, whichever is on the side where
I added the cap,
with a schematic you can verify things quickly....although anything is still
possible....
I believe the problem lies elsewhere just the same....I think that the
control chip, or IC has stopped controlling properly...therefore I would be
led to believe either there is a bad resistor or cap within the 20 pin IC
output circuitry,,funny thing is both tranformers are leaking, meaning thier
running requency if off...or clock for mosfet drivers is off...thoretically
that should not matter, the drivers should produce the right frequency no
matter what....and since it is possible to get the monitor to stay on, this
would lead you to think that the IC is defective....if it was something
burnt then the monitor should not be able to turn on.....it would recieve no
signal somewhere down the line and the mosfets whould shut down....but since
it can be made to turn on, then there must be some clock being producedwrong
somewhere...so with that being said, the IC is still functioning to some
degree.....ANYWAYS.....forget that...

a few things to sum up.....

A: USING THE MONITOR WILL MOST LIKELY CAUSE MORE DAMAGE....
B: Why would both transformers be leaking ??? I dont think both tranformers
are bad....But I have only added one cap to one side,,,,,,,.......

C: I do believe there is a burnt resistor or bad cap in the driver IC
circuitry(u901)....
D: with a schematic in hand you should be able to verify everything...

and last but not least...
E: I have left out a certain cap as well that was burt to a crisp....you
will see it if you look for it....
E: Come by this weekend or whenever and I will loan you a
mutimeter.......then if you do find any bad tiny component I will swap it
out in 5 minutes...
Furthermore, with the schematic I can now add the right value of cap to the
surface mount one that was burnt...I really do think that this is the whole
problem to begin with....


Anyways...take care, talk soon.


1. What Cap where? can't find my self.
2. Do I think that the tubs are bad? I don't think thay are
3. Transformers are arcing to finger.

what do you guys think?

[Mark369]

Re: AG Neovo F-419

I don't know why he did that to my board and charged me $50.00 and 20.00 in mofsets. looks like he didnt replace the other two on the other side. I guss thats good for me after seeing what he did. the photos are after i removed a lot of solder . the photo has sum marks on it showning where i think the cap that he removed. can't realy tell with all the solder milted to the board. i have used the wick and flux maybe to much flux. what's good to remove flux form surface of board.

Thanks guys.

When guys like you help out dummie's like me. i think the world isn't all that bad.

[PlainBill]

Re: AG Neovo F-419

I don't know why he did that to my board and charged me $50.00 and 20.00 in mofsets. looks like he didnt replace the other two on the other side. I guss thats good for me after seeing what he did. the photos are after i removed a lot of solder . the photo has sum marks on it showning where i think the cap that he removed. can't realy tell with all the solder milted to the board. i have used the wick and flux maybe to much flux. what's good to remove flux form surface of board.

Thanks guys.

When guys like you help out dummie's like me. i think the world isn't all that bad.

Sorry, I have to disagree with you. You aren't a dummy. You are untrained, unskilled, and inexperienced. Those can be corrected easily. The dummy is the guy you took this to. I don't think his failings can be easily corrected.

PlainBill

[Krankshaft]

Re: AG Neovo F-419

Based on the way that guy wrote he seems utterly clueless. Also complete sentences and using the enter key wouldn't hurt either.

I have no idea why he would blob up the source and drain pins they are all connected internally inside the package. I think they were blobbed because he doesn't know how to solder SMD packages correctly.

It does seem like this guy just made the damage worse.

[Mark369]

Re: AG Neovo F-419

yea i know but i wan't to fix it. And this is the way i am learing how to from the internet and guys like you. I could by a new board for $45.00 USD + Shipping and all costs to canada would be like $100.00.

I know buying a new board would prob. cost less the i have spent or what im going to spend but thats ok with me. it's worth it to learn it well still cost less and i can still keep my day job then if i were to take a corse some where.

I know he could of used a heat gun to remove and replace the smd.

[Mark369]

Re: AG Neovo F-419

don't know if any one wants to help me. I mean for guys who know what they are doing it is prob not that hard.

[PlainBill]

Re: AG Neovo F-419

don't know if any one wants to help me. I mean for guys who know what they are doing it is prob not that hard.

For someone with the skills and equipment (and parts), repairing this may be possible. I doubt it would be easy; we don't know what the other guy ruined in his attempts to repair it. For a start, I would at least scope the controller IC, looking carefully at the drive waveforms. Then I would test every other semiconductor in the area, and check each resistor that might have been damaged. Ringing the transformers would also be a very good idea.

The problem from my point of view, I don't believe you have the skills or equipment. The alternative approach would be to replace the controller IC after testing every transistor, etc. And frankly, I don't see it worth the effort.

This is not to insult your abilities; no amount of studying is going to replace an oscilloscope and ring tester.

PlainBill