Samsung 912N Problem

[LAS]

Re: Samsung 912N Problem

Thank you for your response retiredcaps. Those are good questions and I will answer them this holiday weekend. As to Nothing, the screen goes dark, ie the backlights switch off. Blue power light also goes out at that time too. Then I unplug the VGA cable and then I can turn it back on again and get the screen saver. And I have tried a couple different VGA cables. And I will post logic board photos as well.

[LAS]

Re: Samsung 912N Problem

Front and back of the logic board:

[LAS]

Re: Samsung 912N Problem

Perhaps something here: on post #1, the heatsink on the bottom of the left hand photo is energized with about 70v. Is this normal?

[retiredcaps]

Re: Samsung 912N Problem

Front and back of the logic board:

What is the part number for IC600 and IC201?

[retiredcaps]

Re: Samsung 912N Problem

Perhaps something here: on post #1, the heatsink on the bottom of the left hand photo is energized with about 70v. Is this normal?

Heatsinks are likely live. Since your power mosfet is probably attached to that heatsink, it will register high voltage.

[retiredcaps]

Re: Samsung 912N Problem

1) IC601 is APL5522. Datasheet is attached

2) Measure pins 1-4 while using pin 7 for GND (black probe).

3) Report readings.

[LAS]

Re: Samsung 912N Problem

IC601 (APL5522)
Pin 1 3.3v
Pin 2 4.25v
Pin 3 4.2v
Pin 4 2.5v

IC201
A81SC
C423

[LAS]

Re: Samsung 912N Problem

As to IC201, I did a little online research as well as here on Badcaps, and it looks like it cross references to 24C08 if I'm not mistaken. With that, I was able to find a datasheet and this is what I found with the black probe on pin 4 Vss (ground):

1 less than 1v
2 less than 1v
3 less than 1v
4 Ground
5 SDA (Serial Address/Data IO) 5.11v
6 SCL (Serial Clock) 5.1v
7 WP (Write Protect input) 5.11
8 Vcc (+) 5.11 and spec calls for 4.5-5.5

I'm not familiar enough with this package to know if it's good or bad, but should the whole top row all be at 5.1v?

[retiredcaps]

Re: Samsung 912N Problem

IC601 (APL5522)
Pin 1 3.3v
Pin 2 4.25v
Pin 3 4.2v
Pin 4 2.5v

IC601 is fine. What is part number for IC600?

[LAS]

Re: Samsung 912N Problem

IC600
A43AG
FDS9933A

I googled each number, and while I came up with a part # for A43AG, the package didn't match. I googled FDS9933A, and it looked more like the part on the board. Datasheet is attached below. A dual channel 2.5v specified Power Trench MOSFET. Finding myself on a roll, I took some voltage measurements using a mounting screw as a ground point:

Pin 1 S1 12.4
Pin 2 G1 12.4
Pin 3 S2 5.0
Pin 4 G2 .5
Pin 5 D2 5.0
Pin 6 D2 5.0
Pin 7 D1 0
Pin 8 D1 0

[retiredcaps]

Re: Samsung 912N Problem

FDS9933A

Test this mosfet for shorts. See section 2 Shorted Transistors/MOSFETs

https://www.badcaps.net/forum/showpo...4&postcount=19

[LAS]

Re: Samsung 912N Problem

S1 and G1 measure .2 ohms;
S2 and G2 measure .3 ohms.

The two D1 pins look like they are joined together on the schematic, as do the two D2 pins.

All measurements are done with the chip out of the circuit and on my dining room table. It was also the first smd component I have ever removed from a board, and it went easier than I expected. Putting it back is another matter, but I'll get it in.

Looks like two shorts, yes?

[retiredcaps]

Re: Samsung 912N Problem

S1 and G1 measure .2 ohms;
S2 and G2 measure .3 ohms.

Putting it back is another matter, but I'll get it in.

Looks like two shorts, yes?

1) Shorted. Replacement at digikey for 99 cents.

http://search.digikey.com/us/en/prod...ACT-ND/1849924

or Newark for 59 cents + 15% off

http://www.newark.com/fairchild-semi...6?Ntt=FDS9933A

2) I like this video for soldering SMD (short 9 minute video)

http://www.youtube.com/watch?v=3NN7UGWYmBY

[LAS]

Re: Samsung 912N Problem

Oh, my I finally get to use my coupon!!!

I will also be ordering an NPN transistor to calibrate my soon-to-be-arriving Blue ESR tester kit. My bill just doubled.

Thanks Retiredcaps. Your insight is very much appreciated. I will get back to the list as soon as I make the repair and will report how it went.

LAS.

[retiredcaps]

Re: Samsung 912N Problem

At 58 cents, I would get 2 since it is your first SMD solder attempt. If all goes well you will have a spare.

[LAS]

Re: Samsung 912N Problem

This good advice Retiredcaps. I also watched the Youtube video last night - that guy is really good at what he does and my big takeaway was flux, flux, flux.

[smason]

Re: Samsung 912N Problem

I had read earlier about the use of an 1157 auto bulb - but I was mistaken. .

You probably read about using an 1157, but as a load for the power supply.

I often use one just to see if the supply can handle a load, sometimes the 12v supply will measure fine, until you put a load on it.

Really the best substitute for a suspect CCFL, is a known good CCFL.

Now and then I get an unrepairable monitor (broken screen, MCU made from unobtainium) and I'll keep the CCFLs for testing.

[LAS]

Re: Samsung 912N Problem

That's interesting smason. When you put a load on a bad 12v power supply, what happens? Does the reading go way down? Pop a fuse?

Also, can anyone recommend a source for a Samsung ccfl wire assembly for testing purposes? Digikey? Mouser? CCFL Warehouse?

[smason]

Re: Samsung 912N Problem

That's interesting smason. When you put a load on a bad 12v power supply, what happens? Does the reading go way down? Pop a fuse?

Usually the output voltage just drops, or disappears. Depends on what's wrong with the supply. Most often it just works, which tells me the power supply is fine, and to concentrate on other circuits.

Here's an example. Plasma TV, dead. No 12v. Unplug the Z sus board and the 12v is fine. Is it the Z sus shorted, causing the 12v to drop, or is it the power supply unable to supply the Zsus?
Quick easy test, clip an 1157 on the power supply with the Zsus disconnected. If it lights bright, and the 12v stays stable, bad Zsus.

Though technically you could measure the resistance of the 12v inpit to the Zsus and see it's shorted, but that's an example.

[retiredcaps]

Re: Samsung 912N Problem

Also, can anyone recommend a source for a Samsung ccfl wire assembly for testing purposes?

1) These guys have some pre-harnessed ones on blowout sale for $4.50. I can't tell from the picture if they are the typical 2 wire connector or not.

http://ccfldirect.com/blowoutlamps.html

Shipping is $3.99 for USA customers.

The pre-harnessed ones are really nice and easy to replace.

Give them a call or send them an email.

2) I know budm has an entire stack of them from his volunteer job at the recycle facility.

https://www.badcaps.net/forum/showpo...2&postcount=32