Samsung SyncMaster 940T blows inverter fuse

[theviper902]

Re: Samsung SyncMaster 940T blows inverter fuse

back from the dead. but I have the 940t blue power light comes on but no picture. so I opened it 3 820uf caps were bad replaced them. still same prob power light on no picture. but computer recognizes it as being there just no display. is this related to needing the inveter fets with the part number above? thanks guys

[senndogg]

Re: Samsung SyncMaster 940T blows inverter fuse

another history of success in replacing the inverter FETs

replaced them with AF4502C from ebay. now its working great!

thank you guys! yo're awesome!

[Toasty]

Re: Samsung SyncMaster 940T blows inverter fuse

Yours was not blowing a fuse. This one (stevenps) is confusing enough.

I suggest starting a new thread?

With any luck, the schematics we have will match yours.

Is this the one you were talking about on post #111? The tight fit one?

You don't identify the LCD in that post. Is it a 940T?

If not, what is it?

Good shot of the back and identify any IC's please.

Copy and paste all you talked about so far into the new thread.

Toast

[mockingbird]

Re: Samsung SyncMaster 940T blows inverter fuse

I replaced every last one of them. Sorry, this isn't the recap. I'll try to get a picture of it on tommorow. You think I should replace the big one maybe? I hope I didn't blow an IC. Otherwise I'll have to toss this in the trash.

[Toasty]

Re: Samsung SyncMaster 940T blows inverter fuse

That's a photo of the recap? Can't be...?

Ticking is the PWM trying to fire. Sounds like a wrong cap or you didn't replace them all, sans main cap.

Voltages?

Toast

[mockingbird]

Re: Samsung SyncMaster 940T blows inverter fuse

Oh well, this recap didn't last long. A few minutes into using it it started making clicking sounds. I attributed this to coil vibration since I removed some tack. Now it won't turn on at all (Like the light won't even turn on, no power whatsoever).

Any ideas what could have blown here?

[Toasty]

Re: Samsung SyncMaster 940T blows inverter fuse

Is there a chassis number somewhere? I see 2 different ones for the 940T.

My advice for resistance checking was not clear enough. I was trying to suggest a broader scale of checking, rather than a component-by-component check. For example, pick a transformer leg and go back to the 4 BIT IC outputs, or to the power input to the board. It might help narrow this faster. Then, if you found a mismatch, you could go component by component back up the path of the difference.

Do the transformers get warmer on the failed monitors than on the "good" one over the same time period?

Toast

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

>>Getting the old ones off the board was a real pain - they acted like they were glued down. <<

Most likely they were. Otherwise the hot air stream used to solder them could make them move or blow them off. Process is: apply solder paste to all pads and glue dots as needed, mount components, allow paste to cure, solder process.

Better way to take these off with a soldering iron is with Chip Quik and something to apply upward pressure (pin). A hot air station is the best as you can get all the solder liquid and then lift it or twist it to break glue.

Ah, that explains why it was so difficult. I ended up using a variant of that idea, but I was only able to lift one side at a time. I think I won't do this to the other monitors, as I'm more likely to damage it than make it better.

Suggestion: Try comparing the good board to the bad ones using an ohmmeter. I had a similar chase in an power supply thread here last year. The problem was finally found by the poster using this method with a new board. Turned out to be a transistor in an area not even being considered. Start at the transformers and work backwards.

Toast

I'll try that if nothing else works. There are a ton of components on the board, and it'll take a lot of work to check them all (and make sure I didn't skip any).

EDIT: Which schematic did you get from Elektrotanya? There are several. Only one I found with the inverter schematic is not the same as yours. Different driver FETs (AM4512C). BUT the inverter Driver IC is a Fairchild FAN7310 and is a 20 pin package. If you look at Page 8, it shows the timing of the outputs. None are supposed to come on at the same time and looks very similar to the 1st trace picture in your post #129.

If it turns out the BIT3195G is bad, I have not found one available other than through a RFQ type of site. They typically won't talk to you unless you need 100 pieces or more.

None of the service manuals listed on Elektrotanya match this monitor for some reason. I think they do match other models listed like the 740N, but not my 940Ts. The timings off the inverter IC as shown in the picture you mentioned match up reasonably well for both the good and bad monitors, so I don't think there's anything wrong with the inverter IC. It looks more likely that there's something going on between the inverter IC and the FETs, and I bought a capacitance meter yesterday to help me track this down. I'm suspecting C213 and C214 because the signal looks different at the gate of the FET on a bad monitor than it does on a good one. I'm hoping that one of these is bad and that I'll be able to substitute to fix it.

[Toasty]

Re: Samsung SyncMaster 940T blows inverter fuse

>>Getting the old ones off the board was a real pain - they acted like they were glued down. <<

Most likely they were. Otherwise the hot air stream used to solder them could make them move or blow them off. Process is: apply solder paste to all pads and glue dots as needed, mount components, allow paste to cure, solder process.

Better way to take these off with a soldering iron is with Chip Quik and something to apply upward pressure (pin). A hot air station is the best as you can get all the solder liquid and then lift it or twist it to break glue.

Suggestion: Try comparing the good board to the bad ones using an ohmmeter. I had a similar chase in an power supply thread here last year. The problem was finally found by the poster using this method with a new board. Turned out to be a transistor in an area not even being considered. Start at the transformers and work backwards.

Toast

EDIT: Which schematic did you get from Elektrotanya? There are several. Only one I found with the inverter schematic is not the same as yours. Different driver FETs (AM4512C). BUT the inverter Driver IC is a Fairchild FAN7310 and is a 20 pin package. If you look at Page 8, it shows the timing of the outputs. None are supposed to come on at the same time and looks very similar to the 1st trace picture in your post #129.

If it turns out the BIT3195G is bad, I have not found one available other than through a RFQ type of site. They typically won't talk to you unless you need 100 pieces or more.]

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

That appears to be about the only thing left. The picture of the board doesn't give enough detail to figure out the circuit, but there appears to be a resistor and capacitor in parallel between the output of the inverter controller and the gate of the FET.

I don't think R217 is involved there - it looks like inverter IC pin 8 has R316 between it and the FETs, and pin 9 has C213 and C214 in series between it and the FETs. I'll get a better picture, and check if there's a trace running under C213.

[PlainBill]

Re: Samsung SyncMaster 940T blows inverter fuse

I also got some (hopefully) more useful pictures from my scope. These are comparisons between the good (blue and green) and bad (red and yellow) monitors showing both the pin 8 output from the inverter IC and another signal (one is pin 9, the other is the drains of the FETs). I think the most interesting one is the output from the FETs - instead of being an interesting-looking, square-like wave (like the blue line), the bad monitor has a sine-looking segment (yellow line). I'm not sure what that means or what causes it, but it corresponds to a slight difference in the signal at pin 4 of the FETs. The good monitor is flat in those locations, but the bad monitor shows a slight increase in voltage when the signal should be low (see Pin8-Pin9Gate-U202Drain.png for a comparison of all 3 signals from the bad monitor). Perhaps C213 or C214 is bad?

That appears to be about the only thing left. The picture of the board doesn't give enough detail to figure out the circuit, but there appears to be a resistor and capacitor in parallel between the output of the inverter controller and the gate of the FET.

PlainBill

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

I also got some (hopefully) more useful pictures from my scope. These are comparisons between the good (blue and green) and bad (red and yellow) monitors showing both the pin 8 output from the inverter IC and another signal (one is pin 9, the other is the drains of the FETs). I think the most interesting one is the output from the FETs - instead of being an interesting-looking, square-like wave (like the blue line), the bad monitor has a sine-looking segment (yellow line). I'm not sure what that means or what causes it, but it corresponds to a slight difference in the signal at pin 4 of the FETs. The good monitor is flat in those locations, but the bad monitor shows a slight increase in voltage when the signal should be low (see Pin8-Pin9Gate-U202Drain.png for a comparison of all 3 signals from the bad monitor). Perhaps C213 or C214 is bad?

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

I received my replacement transistors today, and the replacements did exactly the same thing the originals did. Getting the old ones off the board was a real pain - they acted like they were glued down. I actually melted one of them in half trying to get it off. Either the originals overheated and I overheated the new ones trying to get them installed, or there was nothing wrong with the originals.

[PCBONEZ]

Re: Samsung SyncMaster 940T blows inverter fuse

@PCBONEZ:
The 2 caps given, are too tall (30mm). Clearance is limited to 20mm.

Sorry, didn't read back far enough.

I noticed that the Capxon sheet seemed "off", but couldn't place what was wrong. From what I see, it seems they take caps from everyone/everywhere, some from this pile and some from that, just to build a sheet. Q

It's like that in a lot of crap brand data sheets.
.

[Quasar]

Re: Samsung SyncMaster 940T blows inverter fuse

@PCBONEZ:
The 2 caps given, are too tall (30mm). Clearance is limited to 20mm.

I noticed that the Capxon sheet seemed "off", but couldn't place what was wrong. From what I see, it seems they take caps from everyone/everywhere, some from this pile and some from that, just to build a sheet.

Q

[stevenps]

Re: Samsung SyncMaster 940T blows inverter fuse

Looks like Newark will be getting this order and not Digikey. How's their shipping costs?

Shipping is something like $5 via USPS Priority Mail. They do some interesting packaging - they put your caps in a plastic bag, put that in a bubble mailer (they do this part for each part # you order), and put those in a box.

[PCBONEZ]

Re: Samsung SyncMaster 940T blows inverter fuse

FK come both as SMD and Radial.
The letter right before 'FK' is different in the full Part Number.
EEUFK = Radial
EEEFK = SMD
EEVFK = SMD

A 10x20mm Capxon KF would be around 1320/.065 or so.
An FC or PW in 10mm would be good enough.
http://search.digikey.com/scripts/Dk...me=493-1832-ND
http://search.digikey.com/scripts/Dk...name=P11223-ND


The Capxon KF data sheet is erratic.
What I mean is using FC and PW for some KF is fine but for others FC and PW aren't good enough.

.

[mockingbird]

Re: Samsung SyncMaster 940T blows inverter fuse

Ok so here's what I got on Newark per Quasar and StevePS' help, with guidance from Momaka's Capxon Replacement Table.

2 x Panasonic FK 25V 820uF - Newark 32R9027
3 x Rubycon ZL 25V 220uF - 38M3273
1 x Panasonic FC 10V 2200uF - 25M9153
1 x Nichicon PM 10V 1000uF - 65R3529
1 x Rubycon YXG 50V 22uF - 38M6869

This list accounts for what's in stock. That's why I have to mix manufacturers.

[mockingbird]

Re: Samsung SyncMaster 940T blows inverter fuse

Link to Newark's page on the FK 820s (my edit window expired):
http://www.newark.com/panasonic/eeuf...ial/dp/32R9027

Ah thanks, I did manage to find it. Funny, Digikey has an "FK" section that's all SMD caps.

Looks like Newark will be getting this order and not Digikey. How's their shipping costs?

If they say they squeezed it in there, I believe it. There's a lot more trust in their manufacturing.

Yea, but keep in mind, it's 820uF. Some of the other MFGs also have the part in the size, but none of them have a part as low an ESR IIRC.

[Quasar]

Re: Samsung SyncMaster 940T blows inverter fuse

I'd trust Panasonic any day. If they say they squeezed it in there, I believe it. There's a lot more trust in their manufacturing.