Samsung Syncmaster 223BW - blank screen..

[budm]

Re: Samsung Syncmaster 223BW - blank screen..

You mean it show 0 Ohm that Cap? If that is the case, the load is shorted (You can remove that cable from that connector to see if the resistance will still show 0 Ohm), or shorted out MLCC (Multi Layer Ceramic Capacitor, C436) which is connected in parallel with the 100/ 16V cap.
As you can see, there will always be MLCC in parallel with the Electrolytic cap, the MLCC is usually around 0.1uF. Failure mode of MLCC is shorts.

[neuralnet]

Re: Samsung Syncmaster 223BW - blank screen..

I get nothing registered on that cap C435 (0 ohms). The others register a solid 105 - 125 ohms. The cap directly below C435 (i.e. C629) briefly shows 150 ohms and then falls to 0. I will test the gate pin when my woman comes home! cheers.

[budm]

Re: Samsung Syncmaster 223BW - blank screen..

Take the resistance reading on the Two legs of that 100/16j cap (no power to the unit).
As you can see, the output pin of the MOSFET has the White triangle pointer next to the pin. No luck finding the info for the MOSFET (it may be Dual-MOSFET) yet.
One thing is that the In that shows 4.74V (this in is more likely to be the Gate pin) should change state when the monitor is turn and turn off.

[neuralnet]

Re: Samsung Syncmaster 223BW - blank screen..

Thanks for the reply Budm. Are all the small caps rated the same then? They all have 100 16J but different preceding numbers.

I've not replaced the cap yet but I've checked the voltages on IC401. On one leg I'm getting a steady 5.21v and 4.74v on the opposite leg. I'm not detecting voltages on any of the other legs when the power button on the front panel is pushed.. although holding 2 probes and pushing the button at the same time is kinda tricky I will double check to make sure when I have another pair of hands to assist me.. I have also tested for voltages with a VGA cable connected to a running computer & am only showing the same 5.21v and 4.74v.

IC401 has '38881' stamped on top, how can I find the pinouts for this? I thought MOSFETs had 3 legs, but this has 6.

Should I replace the cap before going further ? Where to next Budm ?

[budm]

Re: Samsung Syncmaster 223BW - blank screen..

That is the switched 5V for feeding the T-CON board on the LCD panel assembly, it is switched through the MOSFET IC401. That main board will send out BL_ON signal and Dim signal to turn on the inverter circuits, it also sends out signal to supply the voltage to the T-CON board. This will happen when the monitor detects the video signal from running PC, when you first turn on the monitor, those signals will be present for 3~5 seconds, then they will go away if the video signal is not detected, the monitor will go into standby mode.
So check and see if you do have 5V on at least one pin of the MOSFET or not, you also need to get the pin out of the MOSFET to check out the Gate voltage to see if it is present or not, this Gate voltage should change state when the monitor is power on /off (or when video signal is present and not present).
That cap is 100uf 16vdc.

[neuralnet]

Hi component peoples, I'm in need of some assistance fixing a Samsung Syncmaster 223BW. I've done the basic diagnostics and here's what we're dealing with;

The power button works, but pressing it gets no results... no blue leds, no output to screen. The power board is outputting 14.5V (close to the specified 13.5V).

The IP board (Model: Mendel_VE, Code: BN41-00885B) has handy contacts on the reverse for you test the voltages and I'm getting the 1.8V and 3.3V outputs but nothing on the 5V circuit.



I've identified a cap with high ESR and very low resistance in the 5V circuit. A different cap (position C725) with the same markings gets very similar values to the other caps on the IP board.. This is where I get stuck. I've googled the markings on the bad cap "24347 100 16J" (position C435, top middle of pic, right of the ribbon connector) and can find nothing useful on the net.

When I checked the forum for other posts on the same monitor, user Scenic has the same IP board as mine and although there's a link to the schematics in this thread, the schematics are incomplete, the image of the IP board in the PDF is not the same as mine and the components have different location identifiers. I can't read what's printed on Scenics caps either thanks to the low res images (front & back). I've looked hard for a full schematic diagram of the same revision of my IP board but no success..

Does anyone know what rating "24347 100 16J" is? I'm used to being able to read off the old capacitor so I know what to use as a replacement.. I don't often have to replace SMT caps. How can I find out what cap I need to replace C435 with? Thanks!