Repairing LCD monitor

[sean87]

Hi guys,

There is a Samsung S22A300B monitor that I am trying to diagnose and possibly, repair.

The monitor has DVI and VGA inputs. It runs from an external 14V/2.5A DC adapter.

When there is no video cable connected (DVI and or VGA), the monitor goes to self test mode as expected...showing that famous screen with title "Check signal cable" and 3 RGB squares. In this mode everything is normal, the backlight is also on and no problem...



As soon as I connect either DVI or VGA or both of them (of course on the other end these cables are connected to PC and pc is ON),  The backlight goes off, screen becomes black, but the LED for power on, on the monitor remains ON.

I've cracked the monitor open and there is only a tiny PCB for the connectors and some circuitry and sockets for backlights. There are some test points like 3.3, +5, SDA, SCL and LED that multimeter shows they are fine.

The only thing I could notice, is that one of the chokes is a little bit sticky, and it produces more noisy sound than the other chock.

There is also a solid capacitor that I believe  is in series with the DC input jack...the multimeter shows 14.5 volts across this cap. It is also has something like what normal electrolit capacitors have on their top...some sort of breathing crack!!!! Maybe the pictures can speak better.




Any ideas what can be wrong? What kind of other tests I can do to get closer to the failure reason?

I am sure this is not the problem of my PC, I have 2 other (different) monitros that still work fine with my PC....this one just suddenly died or faked death in a beautiful sunday morning

[sean87]

I have a feeling that something is going wrong under the metal shield, but it is almost next to impossible to desolder this metal shield...even with my soldering iron at 420 degrees this solder joints are not even melting!

[sean87]

Nevermind, I found that this is a common problem with SA300 series of monitors...there is only one soloution and it is to update the monitor firmware (YES! using vga cable!) ....I did that also but it didn't help... 

[Alana]

I have 2 samsung LCD's from dumpster diving - one had cracked solder in the connectors from connecting and disconnecting cables frequently. Behaviour like in yours. Solution - even if it looks ok resolder each pin with normal leded solder and check for pcb traces that may have gone bad.
There should be bunch of input protection diodes [transils?] in SOT23 packages near VGA and DVI - at least this was a case in my LCD.
Other - bad solder, propably within firmware chip. Reflowing this chip fixed a problem.

Try both solutions, one may work for you.

[madires]

There is also a solid capacitor that I believe  is in series with the DC input jack...the multimeter shows 14.5 volts across this cap.

It's a fuse ;-)