Samsung T240 input switching issue

[cobraf]

Hi guys,

I went over the posts regarding this monitor

The issue started about a month ago, when i turn the monitor on it would not display a pictutre but started to go through the inputs (Auto search)
When the correct input is found DVI,i can see a picture but every few seconds the picture goes on and off, and the orange led turns off and then off at the same time, this behavior can go on for some time and then it will cycle through the inputs again.

I have replaced some of the caps since i could not find the other ones at my local electronics store, the original caps do not show any signs of bulging, i have also tested them with a multi meter out of circuit and the measure fine.

i have also replaced the transformer TM-09175 although the old one seems to be fine as well, the legs measure around 950OHM and on the new one around 1000 ohm.

After replacing the transformer and caps, the monitor started working ok, but after an hour or two i started hearing a buzzing sound from the back and an hour after the old behavior came back.

I have also tested the caps C104 and C103 and the measure 2 nF, i have looked in the service manual and they show to be
....4
C103
2203-000888
C-CER,CHIP;4.7nF,10%,50V,X7R,TP,1608
1
S.A
....4
C104
2203-000888
C-CER,CHIP;4.7nF,10%,50V,X7R,TP,1608
1
S.A

Can anyone offer any advice on what to look for next?

Also the small caps on near the output connectors
C301-C305 i tried measuring them in circuit but my fluke shows OL, from the specs they seem to be less then 1nF so they are out of range for this Fluke.

I can order a whole power board from Ebay, but first of all i am looking forward to fixing it myself and also, not 100% sure that the issue is with the power board.

[cobraf]

Re: Samsung T240 input switching issue

No one has any suggestions?

[cobraf]

Re: Samsung T240 input switching issue

Found a video on youtube that shows the exact same behaviour i have on my T240

http://www.youtube.com/watch?v=r7m5-JSPYF8

Can it be the transformer? Can anyone tell me how to test the transformer on the AC side?

Since i already replaced the inverter transformer i'm kinda running out of ideas

[cobraf]

Re: Samsung T240 input switching issue

Ok so i pocked around with the fluke just testing the components and found some diodes that look like they are blown

D103 a small glass diode that is located right next to the 47uF cap,from what i gather its

D103
0403-000258
DIODE-ZENER;BZX84C5V6,5.2-6V,225mW,SOT-2

Another Diode between the heat sink and the 47uF cap also shows over 1.12V with the black probe on the other side from the line.

This one marked ZD101, have no idea what the model is

Also found another one D107 also looks like its bad next to the array of caps just up the circuit, next to the 2 resistors
In the parts list of the service manual this one is listed as
D107
0401-000008
DIODE-SWITCHING;DAN217,80V,100MA,SOT-23,

The 2 resistors next to the diode
first is Green Black Red Gold This one goes all over the place,cant get an exact reading
Second Blue Silver Black Gold (R105) reads 67.2 Ohm

[Rtech]

Re: Samsung T240 input switching issue

Connect the PSU/inverrter ONLY ie NOT THE LOGIC Board to the Mains input,and you can then do a number of test which should help.BE very careful of large Dc voltages particularly on the large capacitor.Measure the DC voltage acdoss that cap, and you can also measure voltages on the connector CN2 which has voltages etc printed on the board, you are looking for the 15V, 5.2 volts and 3.3 volts.Are these there and steady ??you can then plug in the lamps into their connectors ( a test set of lamps may well be a very big help, if you have any ??)Then AGAIN with no logic apply 3v DC, maybe from a battery between the on/off pin and GND on CN2, and see if the lamps come on.If you have a 1K resistor you could use that instead of the battery, between the 5.2v line ,if you have it ??and the on/off pin.

[cobraf]

Re: Samsung T240 input switching issue

Hi Rtech

I did the tests on CN2

15V and 5.2V (which shows 5.3V) are there

But 3.3V is showing 0.3V on CN2 i have checked CN3 as well and the reading for 3.3 is the same

C106 cap reads 2.5V

Also checked the outputs with the logic board connected

the 15V when the monitor is turned on but no lamps connected shows 17.8V
The 5.2V pins show 5.2 normal

3.3V is present

Key 1 and key 2 pins

Key1 shows 3V steady
Key 2 going all over the place from 2.4 to 3.2

[Rtech]

Re: Samsung T240 input switching issue

You need to do the lamp tests next.

[cobraf]

Re: Samsung T240 input switching issue

The lamps come on only with the logic board connected, i will try with a battery and report back