Problems with Samsung 740N monitors

[budm]

Re: Problems with Samsung 740N monitors

The reading error may be due to the bad 8-PIN SMD Power MOSFETs.

[jondoe]

Re: Problems with Samsung 740N monitors

I didn't test it off the board, but I did compare readings with a working, identical board and the two were wildly different, I guess that's not a great way to test it. I'll remove it and test regardless at some point tomorrow.

Thanks!

[budm]

Re: Problems with Samsung 740N monitors

It looks like R217 is connected in parallel (need verification) with ZD201. Did you test the ZD201 off the board?
The Cathode (PIN 3) of ZD201 is connected directly to the B+ for running the inverter circuit.

[jondoe]

Re: Problems with Samsung 740N monitors

In the meantime I've ordered two IRF7319PBF and a BZX84C7V5LT1G. I'm fairly sure those are suitable replacement parts, I'll find out next week!

[jondoe]

Re: Problems with Samsung 740N monitors

I've lifted a number of the large resistors to check them out of circuit, and most of the transistors/large mosfets, they all appear to be OK.

Pictures attached

Edit: I borrowed some cheap calipers, the chip is approx 2.9mm wide at it's longest point, so I suspect this is a SOT23 package.

[budm]

Re: Problems with Samsung 740N monitors

Can we see the straight shot pictures of the top and the bottom side of the board?

[Behemot]

Re: Problems with Samsung 740N monitors

Guess its 7.5 V either single with two pads connected to one end, or two in parallel. Should not matter anyway.

[jondoe]

Re: Problems with Samsung 740N monitors

I haven't quite identified it. I gather it's a 7.5 Zener of some description, I'm rather a novice at this kind of thing. Attached is an image as best I can make of it.

[Behemot]

Re: Problems with Samsung 740N monitors

Have you identified it? Some of them SOT-23 just have single diode with one end connected to two of the pins. Some actually have two diodes in single package (series, parallel or anti-parallel).

[jondoe]

Re: Problems with Samsung 740N monitors

Sounds reasonable, but I wondered as the one installed has three pins, and leaded only has the two legs, how would I solder that in?

[Behemot]

Re: Problems with Samsung 740N monitors

Usually you can replace SMD diode with leaded one.

[jondoe]

Re: Problems with Samsung 740N monitors

Thank you for everyone's input into this thread, I have an ip-35135b from an IBM Think Vantage monitor, which must be a rebadged Samsung.

I've changed the three large filter caps for some 1000uf Suntans and replaced the pico fuse, only for the fuse to blow about an hour or so later. On closer inspection of the two AF4502C, one of them is testing for continuity from pin 3 to pins 5, 6, 7 and 8. That doesn't seem right and isn't reflected by the other. Probing around that circuit I found the ZD201 appears to be faulty, I get 0.2 on a diode test, on a working board it was 0.7, so I suspect it's fried.

Does anyone know the package type/size of the ZD201? I'm not very familiar with surface mounts, but I'm happy to try and replace the mosfets and zener to see if comes back to life for more than a couple of hours

Thanks.

[dinesh111]

Re: Problems with Samsung 740N monitors

thanks................................................

[Venomus28]

Re: Problems with Samsung 740N monitors

So on one monitor i had three bulged capacitors and a blown fuse, can anyone tell me what should i check to know why the fuse blow ?
And on the other one as Th3 uNiQu3 member suggested i have three bulged capacitors, a blown fuse and both mosfets shorted
(The fuse are now both replaced with 3A SDM)

[Venomus28]

Re: Problems with Samsung 740N monitors

Send me the link please

[Th3_uN1Qu3]

Re: Problems with Samsung 740N monitors

You have shorted mosfets in the inverter. See my post above on how to check them.

[Venomus28]

Re: Problems with Samsung 740N monitors

Yes, i did that, the screen turned on for one second then, dark again lol
I bridged the fuse with a wire and now the stand by light pulses on and off ?
Ideas ?

[bidomo]

Re: Problems with Samsung 740N monitors

If you can manage to solder it there…

The back side of the board seems safe to place it being SMD

[Behemot]

Re: Problems with Samsung 740N monitors

If you can manage to solder it there…

[Venomus28]

Re: Problems with Samsung 740N monitors

Up the new one
Bottom the old one