Samsung 240t no backlight

[almoodie]

Samsung 240t 2003 vintage
Uses a power adapter which provides 14V
When I connect the power supply adapter and press the on button the monitor beeps and the power indicator lamp flashes every second or so. Backlight does not come on at all not even for an instant. Pressing any of the control buttons produces a beep but no other response. I have wiring diagrams which I downloaded.

Opened it up, images attached.
Small power board 3" x 1.5" (DC to DC) has 3 Samsung electrolytics, no bulging or leakage. Has 14V input and three ouputs:
GND
VOUT 5V as per specs
SIG 26.6V no idea what this should be but it seems a strange voltage.

Inverter board has 3 TMZ electrolytics 330 microF 35V 105C. From the different make and the solder joints on these caps I assume they have been replaced. Are these replacements quality caps with appropriate ESR, could they have failed again or should I look elsewhere.

The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
1 GND
2 BL_Control 0V
3 GND
4 BL_EN
5 GND
6 GND
7 5V -14,4V
8 GND 14.4V
9 GND 9.39V
10 14V -14.4V (negative)
11 14V -14.4V (negative)
12 14V -14.4V (negative)
13 14V -14.4V (negative)
14 14V -14.4V (negative)
15 14V -14.4V (negative)

I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.

[almoodie]

Re: Samsung 240t no backlight

Here's a closeup of the power supply section of the logic board. Power adapter connects at blue arrow, 14V in. This board then outputs power to the inverter board through 15 wire connector, red arrow.

[almoodie]

Re: Samsung 240t no backlight

Here's a closeup of the power supply section of the logic board. Power adapter connects at blue arrow, 14V in. This board then outputs power to the inverter board through 15 wire connector, red arrow.

Second attempt with image

[Scenic]

Re: Samsung 240t no backlight

i've got a SyncMaster 210T (basically the same unit, just 21" instead of 24")

they don't display the usual "no signal" message when nothing's connected to them.
try hooking it up to a computer, it may work just fine
especially since mine does exactly the same things that you described in the first post.

but check the PSU.. mine had the main switcher cooked beyond recognition..
Check the primary cap and the smaller 50V (?) one near it.. mine were baked dry, which probably set the main switcher on fire... lol

caps in the LCD itself are no problem on my unit as of yet, but i thought about replacing the few thru-hole lytics with polys some day..

as my PSU brick was toast, i'm using a toshiba laptop brick with the same ratings instead. just had to hook up the original cable to it..


edit: that beeping is normal for those monitors. gets kinda annoying after some time, cause the monitor always beeps when you push a button (or rather touch the buttons... as they're touch sensitive buttons..)

[Radio Fox]

Re: Samsung 240t no backlight

...The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
1 GND
2 BL_Control 0V
3 GND
4 BL_EN
5 GND
6 GND
7 5V -14,4V
8 GND 14.4V
9 GND 9.39V
10 14V -14.4V (negative)
11 14V -14.4V (negative)
12 14V -14.4V (negative)
13 14V -14.4V (negative)
14 14V -14.4V (negative)
15 14V -14.4V (negative)

I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.

What puzzles me even more than the -14.4V, is why are you getting 2 different voltages on pins that should be GND?

The circuit board usually connects all the GND connections together.

[Radio Fox]

Re: Samsung 240t no backlight

As for the -14V. Have you measured the voltage polarity of the adapter?

You haven't got the polarity reversed have you?

[almoodie]

Re: Samsung 240t no backlight

i've got a SyncMaster 210T (basically the same unit, just 21" instead of 24")

they don't display the usual "no signal" message when nothing's connected to them.
try hooking it up to a computer, it may work just fine
especially since mine does exactly the same things that you described in the first post.

but check the PSU.. mine had the main switcher cooked beyond recognition..
Check the primary cap and the smaller 50V (?) one near it.. mine were baked dry, which probably set the main switcher on fire... lol

caps in the LCD itself are no problem on my unit as of yet, but i thought about replacing the few thru-hole lytics with polys some day..

as my PSU brick was toast, i'm using a toshiba laptop brick with the same ratings instead. just had to hook up the original cable to it..

edit: that beeping is normal for those monitors. gets kinda annoying after some time, cause the monitor always beeps when you push a button (or rather touch the buttons... as they're touch sensitive buttons..)

I have tried using an input from a computer into the VGA input but it makes no difference.

I replaced these two caps, happened to have new caps to suit, but it makes no difference. This board, DC to DC, outputs 5V as per specs. Will however replace the other two caps when I get them from Digikey.

Al Moodie.

[almoodie]

Re: Samsung 240t no backlight

What puzzles me even more than the -14.4V, is why are you getting 2 different voltages on pins that should be GND?

The circuit board usually connects all the GND connections together.

Agreed, but I checked my values again and they are the same. My only way to go at the moment is to replace the three electrolytics on the power section of the logic board, 3 @ 100 micoF 16V 105 C, when they arrive.

[almoodie]

Re: Samsung 240t no backlight

As for the -14V. Have you measured the voltage polarity of the adapter?

You haven't got the polarity reversed have you?

Adapter is brand new and I have checked the input, it reads +14V at entry to the DC to DC inverter board.

There is no way to reverse the polarity of the adapter it is a 4 pin DIN plug that will only fit one way.

I will wait for my order from Digikey to arrive and complete the replacement of all electrolytic caps. Otherwise I can't see any burnt components or dry joints.

[Scenic]

Re: Samsung 240t no backlight

hmm.. i think i'm gonna hook mine up and check the voltages... if that helps..

[stignatious]

Re: Samsung 240t no backlight

any word on voltages for this monitor? I've got the same issues with a 210t
thanks

[pedro]

Re: Samsung 240t no backlight

Samsung 240t 2003 vintage

The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
1 GND
2 BL_Control 0V
3 GND
4 BL_EN
5 GND
6 GND
7 5V -14,4V
8 GND 14.4V
9 GND 9.39V
10 14V -14.4V (negative)
11 14V -14.4V (negative)
12 14V -14.4V (negative)
13 14V -14.4V (negative)
14 14V -14.4V (negative)
15 14V -14.4V (negative)

I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.

Maybe just a DOH! moment?

Just eyeballed those with the order/readings reversed. Assuming you had your meter connected to what you thought was a ground pin (1) but was actually pin 15, you get the following:

1 GND 0V
2 BL_Control 0V
3 GND 0V
4 BL_EN 0V
5 GND 0V
6 GND 0V
7 5V -14,4V 5V
8 GND 14.4V 0V
9 GND 9.39V 0V
10 14V 14.4V
11 14V 14.4V
12 14V 14.4V
13 14V 14.4V
14 14V 14.4V
15 14V 14.4V

I hope I have transposed them all correctly, and you follow what I'm getting at.