Samsung SyncMaster T240 - 2 seconds then black problem

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

The jumper is probably an innocent bystander. It looks thick enough to handle the expected currents without heating up enough to darken the board. Hard to tell from the pictures, but it looks like the transformer might have blown smoke, or maybe even an arc, out along the general direction of the core. Since there were apparently previous repairs, it might have been the previous transformer that occupied that position which did this.

It would help to have better pictures, or even better, the actual board to see, but I was thinking along the lines of a bad solder joint that started off with a high resistance and eventually went open.

PlainBill

[mathog]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I think the 20 watt rating is overkill. Do the math. The current of most CCFLs is in the 4-6 ma range. 600 volts, 100K ohm, 6 ma, 3.6 watts. Also, if I recall correctly, Wizard suggested 120 K ohm.

I'd think PPC120KW-3JCT-ND would do the job.

It was supposed to be a safety margin in case it ever encountered an inverter that was putting out far too much output voltage. A lot of them seem to drive the output voltage directly off a transformer, where a short on the input side could change the transformer ratio and jack the output voltage way up. Which brings up another question - would a typical DVM's AC measurement of the output voltage be accurate at the high frequencies used by the inverters?

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

It was supposed to be a safety margin in case it ever encountered an inverter that was putting out far too much output voltage. A lot of them seem to drive the output voltage directly off a transformer, where a short on the input side could change the transformer ratio and jack the output voltage way up. Which brings up another question - would a typical DVM's AC measurement of the output voltage be accurate at the high frequencies used by the inverters?

I believe a shorted turn on the input would REDUCE the output voltage. While the turns ratio is increased, the shorted turn acts as a shunt and damps the magnetic field.


It depends on the meter. I would say it is pushing the voltage and frequency limits of many DMMs.

One of the ideas I had was to build a test load. Say a 90K ohm resistor in series with a 10K. The free end of the 90K goes to the inverter output, the free end of the 10K goes to the return line. That means the junction is at 70 VAC. Tie the anode of a schottky diode to the junction, the cathode to a .1uF cap, the other end of the cap is tied to the return line. The DC voltage across the cap will be 10% of the peak AC voltage. Or tweak the resistances a bit and the DC voltage will 10% of the average AC voltage.

It makes a quick way to compare inverter outputs.

PlainBill

[DUCE]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Sorry I didnt get back with my test results sooner. Fixing broken things has become a full time job here lately.

So as PlainBill suggested I swapped the connections and sure enough only one connector will make the CCFL's do the intermittent flash. I provided a modified pic to explain although its not a complicated concept.

So this means bad inverter am I right? I attached a pic of what I figured the inverter to be and its markings are:
TM-10160
TNE 0852 DT

If I am right an inverter replacement is the next course of action. Any hint on a good source for this? If it is hard to source out a direct placement maybe I can figure out its specs and find a suitable substitute.

Any advice welcome here folks!

DUCE

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Sorry I didnt get back with my test results sooner. Fixing broken things has become a full time job here lately.

So as PlainBill suggested I swapped the connections and sure enough only one connector will make the CCFL's do the intermittent flash. I provided a modified pic to explain although its not a complicated concept.

So this means bad inverter am I right? I attached a pic of what I figured the inverter to be and its markings are:
TM-10160
TNE 0852 DT

If I am right an inverter replacement is the next course of action. Any hint on a good source for this? If it is hard to source out a direct placement maybe I can figure out its specs and find a suitable substitute.

Any advice welcome here folks!

DUCE

Not so fast!!! It COULD be a bad inverter transformer. Or it could be something else in the same area.

First step: On the second picture, there is a jumper that runs from just to the left of the transformer to up under the two poorly installed caps. There is a scorch mark at the lower end of this jumper. Resolder the jumper, then retest.

Second step (only if step 1 fails), I need a good quality picture of the bottom of the board; the inverter area is the primary interest.

PlainBill

[severach]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Samsung Touch of Color T240
Panel: Samsung LTM240CT04 TN Film
Power Supply: Samsung IP-54155A BN44-00226D SEM2005 AP4506GEH
Video: BN41-01030A LST24TWHSUV/ZA MST97889CLD-LF USB2514-AEZG TDA7266D PI3HDMI
Button Board: Too hard to remove. The wires are easily broken.

This Samsung T240 powers on with no backlight. No image can be seen with a bright light. This case is odd because as you take it apart it appears the previous owner forgot to put the screws back in. They didn't. This almost screwless case only has two screws to hold the case together. The rest comes apart with a putty knife. It's tough to figure out how to get it apart until you pop the stand mount out of the bottom of the monitor to reveal the screws. It just snaps in there and the rest of the case just snaps together.

All caps look good on the power supply. I pull and test Samwha 820uf 25v C316 and C317, all good. No shorts on complementary MOSFET pair U202 4506GEH. I resolder the transformer with no success.

Each lamp connector has two lamp outputs and the plugs can be shifted to test each lamp separately. With 4 lamps plugged in the backlight comes only for an instant and turns off. With a either lamp pair plugged into CN303 CN304 and CN301 CN302 empty the back light stays on and the transformer hisses for about 2 seconds then turns off. Both lamp pairs work equally well in CN303 CN304. With lamps plugged into CN303 CN304 and only one of CN301 or CN302 the back light stays on for 2 seconds. No help there so I unplug CN303 and CN304 and try CN301 and CN302 individually. The instant flash brightness appears the same. When all lamps are unplugged there is no hiss so the backlight is probably shut off in an instant.

No lamps: Unknown, likely to be only on for an instant
CN301+CN302+CN303+CN304: Instant
CN303+CN304: 2 seconds + hiss
CN302+CN303+CN304: 2 seconds + hiss
CN301+CN303+CN304: 2 seconds + hiss
CN301: Instant
CN302: Instant
CN303: 2 seconds no hiss
CN304: 2 seconds no hiss
CN301+CN302: 2 seconds no hiss
CN301+CN302+CN304: 2 seconds no hiss
CN301+CN302+CN303: 2 seconds no hiss
CN302+CN304: 2 seconds no hiss
CN302+CN303: Instant
CN303+CN301: 2 seconds no hiss
CN304+CN301: Instant

All this tells me is that some faults take longer to detect than others which means that users may report no back light, a back light for an instant, or a 1 second back light rounded up to 2 seconds.

With the lights off I see arcs inside the transformer. One side has major arcing to create the hiss and the other side makes a small arc occasionally. One side is dead and the other is close. The TM-09175 transformer isn't available anywhere so I order the power supply inverter board from eBay. There are at least two versions because none for sale look like mine with the extra two transformers.

SEM2005 and AP4506GEH make quite a nice inverter driver duo.

SAMSUNG ELECTRO-MECHANICS
Halfbridge Inverter Driver IC (SEM2005)
FEATURES
- High Frequency Voltage Mode PWM Control
- Latched Mode Protection
- Totem Pole Output
- Built-in Low Frequency PWM Generator
- Built-in UVLO function
- Adjustable Shut-down time
- Easy Burst Dimming Control
- Variable Protection function

PIN DESCRIPTION

Pin No Symbol I/O Description
1 SDT I Shut Down Timing capacitor 03 07}
2 OVP I Over Voltage Detection Input
3 OLP I Open Lamp Detection Input
4 FB I Error Amplifiers Inverting Input
5 ERO O Error Amplifiers Output
6 SGND I/O Signal Ground
7 PGND I/O Power Ground
8 NOUT O N-type MOSFET Driver Output
9 POUT O P-type MOSFET Driver Output
10 VCC I Power Supply
11 EN I On/Off Control Er Ir
12 CT I/O Oscillator Timing Capacitor 03 07}
13 BCT I/O Burst Dimming® OSC Timing Cap. 03 07}
14 BDIM I Burst Dimming Input
15 RT I Oscillator Timing Resistor 0307}
16 Vref o 5V/10mA Reference Voltage Output

SEM2005 Rev 1.0

The new board is equipped with a TM-10160 transformer. The new board doesn't work and the transformer doesn't hiss. This board has heat damage. CN303 CN304 doesn't light the lamps. A little continuity testing shows the transformer is a single input two output transformer with no feedback windings. The non paired edge contacts on the input side are not connected. My meter shows >2KV on the transformer output that feed CN301 CN302 and 1600v on the transformer output that feed CN303 CN304. The transformer must be shorted across some windings internally on one side and doesn't produce enough voltage to start the lamps.

I return that board and order a second again with a TM-10160. This board works. These power boards look good with a low part count and great labeling. Unfortunately the transformers are junk.

For a TN Film this T240 has a very nice picture and a decent vertical view angle.

[DUCE]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Thanks Plain Bill, sorry I haven't been quicker on my follow ups. Been a week of broken cars, lost hamsters, and general mayhem. Being a single parent aint for wussies.

I re-soldered that jumper as you advised and there is still no output on 'B' connector. So this means inverter/transformer?

I contacted Samsung for a little info and that was a dead end (no surprise really). They were nice enough to get back in 24 hrs though. So no service manual, no part specs, no comparable board listing, nada.

The other poster did solve this by going to an E-pay seller and I am considering the same. One beef I have with that is: is this a faulty design or a faulty part? Fixing the board if possible is better if its a weak design or under speced. If I just have a bad apple then another board may be a whole lot easier than finding compatible parts.

Thanks again to PlainBill and the latest poster.

Fire away folks, I am all ears!

Bruce

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Thanks Plain Bill, sorry I haven't been quicker on my follow ups. Been a week of broken cars, lost hamsters, and general mayhem. Being a single parent aint for wussies.

I re-soldered that jumper as you advised and there is still no output on 'B' connector. So this means inverter/transformer?

I contacted Samsung for a little info and that was a dead end (no surprise really). They were nice enough to get back in 24 hrs though. So no service manual, no part specs, no comparable board listing, nada.

The other poster did solve this by going to an E-pay seller and I am considering the same. One beef I have with that is: is this a faulty design or a faulty part? Fixing the board if possible is better if its a weak design or under speced. If I just have a bad apple then another board may be a whole lot easier than finding compatible parts.

Thanks again to PlainBill and the latest poster.

Fire away folks, I am all ears!

Bruce

One of the laws of electronics is 'Components fail'. The corollary is that overstressed components fail sooner. Some circuits can be designed can be designed conservatively, others it is more difficult. Designing a reliable high voltage transformer is relatively easy.

Ensuring they are built to the design is difficult. Far and away the most difficult part of the process is ensuring the wire used has an adequate insulation thickness. Even sawing a transformer apart, potting it, and examining the windings under a microscope won't ensure it. All it takes is a thin spot where two wires are in contact and it will be more likely to fail.

PlainBill

[DUCE]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Quite true PlainBill.This basic fact holds true across most engineering disciplines, be it electrical or mechanical. I used to design industrial dust collectors and the quote my boss gave me is "its not a matter of if they will fail but when". Electronics is a weak spot for me because I have focused on mechanical and CAD work most of my life. The electrons knowledge I have gained is frighteningly small considering how often I have to rely on electronic devices. I am attempting to change this now (at 40 no less).

So what has got me stumped on this board is finding another inverter transformer that will be compatible. Maybe buying a replacement as the other poster here did is my only option. Seems a waste but I am swinging in the dark unless I can find parts.

[uwi_u]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

Hi there!

Sorry for capturing the Thread, but I've got a slightly different Problem with my T240.

I got it with Description "Sometimes turns off". When I got it, I noticed that it takes a while before the Monitors Backlight will turn on. But then, the backlight flickered. I opened the case and got an Rev 1 PSU. I measured the Secondary Inverter-Coils. 1060 Ohms each (between 1x and 2x respective between 3x and 4x), ~330kOhms between the different coils(between 1x and 3x, respective between 2x and 4x). So i guess, the Inverter is still functional and ordered a set of Caps (low ESR). Soldered them in and no change happened :-( . Could it be due to the highVoltage-Caps on the Sense-Lines(xnF, 3kV)?


Inverter input side
--------------------------------
|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|
|xxxxxxxxxxInverterxxxxxxxxxxxxx|
|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|
|xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx|
--------------------------------
1x-------2x-----------3x------4x Outputpins

[uwi_u]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I should Mention, that I got the whole service-Manual for that monitor. Unfortunately, the PSU isn't described in there....

PS: I'm from germany. So please excuse my bad writing....

[johnnyto1979]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

can some one share service manual for samsung t240? thanks

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

can some one share service manual for samsung t240? thanks

Here's a link.

PlainBill

[art1351]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I have the same symptoms and the same burning around the transformer. I replaced the transformer for $8 on ebay and the monitor is working again. Can anyone else verify this fix?

[Foo56]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I have the same symptoms and the same burning around the transformer. I replaced the transformer for $8 on ebay and the monitor is working again. Can anyone else verify this fix?

This site is a god send, very glad I found it. It's been very helpful to me (a noob at this.. But eager to learn )

I also have the same thing, scortch marks on the topside and underside of the board around the transformer (pics attached).

After reading this thread, I plan on resoldering the jumper and replacing the transformer. Would/should I do the caps too?

I'm slightly lost in part numbers now and I'm unsure of which transformer to get, what did you go for, Art?

Any help is massively appreciated!

Thanks.

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

This site is a god send, very glad I found it. It's been very helpful to me (a noob at this.. But eager to learn )

I also have the same thing, scortch marks on the topside and underside of the board around the transformer (pics attached).

After reading this thread, I plan on resoldering the jumper and replacing the transformer. Would/should I do the caps too?

I'm slightly lost in part numbers now and I'm unsure of which transformer to get, what did you go for, Art?

Any help is massively appreciated!

Thanks.

When faced with several alpha-numeric strings, Google each of them. TM10160 brings up a number of hits.

PlainBill

[waitery]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I too have the same board with the same scorch mark in the same area. I went ahead and resoldered the jumper and purchased a new inversion transformer, but even after installing the new transformer, I am getting inconsistent power to the screen.....two seconds on, then off, four seconds on, then off, etc. It feels like a cold solder joint that needs to be reflowed. Plain Bill, what do you think>

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

I too have the same board with the same scorch mark in the same area. I went ahead and resoldered the jumper and purchased a new inversion transformer, but even after installing the new transformer, I am getting inconsistent power to the screen.....two seconds on, then off, four seconds on, then off, etc. It feels like a cold solder joint that needs to be reflowed. Plain Bill, what do you think>

It could be a loose solder joint, or a loose wire to a CCFL, or a leaky diode.

PlainBill

[waitery]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

So, I went ahead and was testing the 15 volt line. W/O the main board connected, I get 15.27vdc and it is stable. I connect the mainboard and it falls down to 14.90vdc and then the power cuts out. The voltage drop is causing the power supply to quit. After this happens, it just cycles.

PlainBill, can you help me troubleshoot?

[PlainBill]

Re: Samsung SyncMaster T240 - 2 seconds then black problem

So, I went ahead and was testing the 15 volt line. W/O the main board connected, I get 15.27vdc and it is stable. I connect the mainboard and it falls down to 14.90vdc and then the power cuts out. The voltage drop is causing the power supply to quit. After this happens, it just cycles.

PlainBill, can you help me troubleshoot?

I can try. The first step is standard - I want clear, well lit pictures of the top and bottom of your power supply. One of each, taken from direcly overhead, please. A minimum of 1000 x 1000 pixels, please, and attach them using 'Manage Attachments' - below the text entry area.

Also, a brief summary of what components you have replaced, as well as the brand (and series) of the capacitors currently in the board.

PlainBill