Samsung Syncmaster 173s Input signal problem

[EGuevarae]

Hi. I'm new to this forum (posting, I've been reading it for like two months so far, until I feel comfortable with a little knowledge and a soldering iron).
I have a Samsung 173s that turns on, lights the screen, and then displays the "No signal cable" roaming message on screen. It can stay that way for hours. As soon as I connect a VGA cable to the D-sub input, the screen goes black, and the power led starts blinking. If I remove the VGA cable, it again displays the message of no signal. I opened it and removed the two lamps (2 tubes each one, used them on a ToteVision 18" that had a bad inverter, which was replaced with one from a VE500), so right now it has no lamps installed. The monitor is in good condition, and being 17", I don't want to use it for parts if it can be fixed. I don't have a camera right now, but I will in a couple of days. The boards seem good on visual inspection, but I don't know much about electronics, so I don't know where to start looking. Any advice would be really appreciated.
Thanks in advance.

[PCBONEZ]

Re: Samsung Syncmaster 173s Input signal problem

I'm no wiz kid with these (not compared to some other members) but here is the basic idea.

There are 3 main circuits:
- Power supply
- Back light
- Video

Power supply may be 100% built in or partly a power brick (AC adapter).
- At least part of this is working as your back light works.
But that doesn't mean all it's outputs are working.

Back light is the inverter circuit and the the back light tubes.
- Probably not where your trouble is. No back light gives a blank/black screen.

Video section.
- Most likely the problem (either itself or it's not getting power from power section).
This section takes signal from the video card and converts it for display on the screen.
This section also sends a signal to the PC from it's own firmware identifying it's own settings so the PC can automatically adjust to the correct output. (aka Plug n Play)

I would first try a different VGA cable and check the pins in the connectors on the cables, PC, and screen. Cables go bad and sometimes pins get bent or even break off.

Next look closely at the caps and tell us what they are.
Samsung has been know to use poor caps.
Trying to fix other things with bad caps in there can be a huge waste of time.

.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

The lamps are good. They're working on a ToteVision 18" right now.
The inverter lights (used to) light them good, because all the screen was lighted and the "no signal" dialog roamed free in all the screen area.
I have tested with different VGA cables on different computers here (I have some cables and computers here). I normally only messed with software (I'm a programmer) but now I'm starting to get into hardware too, and because of the SW dev, I have 3 or 4 computers around, and the monitor have been tested in all of them (just in case. I used to have a CRT which only worked with nVidia cards... weird).
I now have a camera but it is not that good. I'll post pictures of the boards.
I got this monitor for $30dlls hoping that it can be repaired (the ToteVision was ..), and will really love to use it instead of the CRT in my test bench.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

The power board is not on a brick, is inside the monitor, in the same board as the inverter circuit (the LCD has just two boards on the inside : the video board and the PS/Inverter board). Pics are very crappy, so I'm not going to post them (very blurry).
But here is the list of caps:
1 - 25v 470mf Sam Young LXZ
1 - 400v 100mf SamWha RD 105C
4 - 16v 100mf CapXon KM 105c
1 - 50v 22mf Sam Young

The 400v,25v and 50v are right next to the AC input, and the 4 16v are after the transformer BN26-00012A, which I figure is the one that transforms the Voltage to 12v (just guessing). None of them looks strange, bulging or blown. The voltages from the power board to the video board are 12v (2), 5v (2), 3 GND and two that I think they are the return for the BLON (5v) and Dimmer/Bright (2~2.5v, and when I check that pin, as soon as I touch ground the lamp shines more than normal, and when I take the probes out, it return to normal).
No visible signs of overheating on top or bottom. As soon as the VGA cable is connected between the VGA card and the monitor, the lamps shut off, the power led blinks (green) and no image.The only change in the signals between the boards is the line that I suspect is the BLON : no voltage when the VGA cable is connected (I assume that's why the lamps shut off). This happens even when I connect the cable to a VGA card alone (not in a computer).

Should I apply 5v to the BLON pin to see what happen?

[PCBONEZ]

Re: Samsung Syncmaster 173s Input signal problem

Should I apply 5v to the BLON pin to see what happen?

I have no idea.
What I would do now is trace circuits and work out a schematic.
Injecting a voltage when you aren't sure what's going on doesn't sound like a great idea in general.

Yup, those caps are junk.....

400v 100mf SamWha RD 105C
SamWha is crap for low ESR applications but this is on AC input and not likely to be a problem. If it was bad you probably wouldn't be getting any life at all out of the thing.

Sam Young is Korean based and at least loosely affiliated with Chemicon.
I think they make caps for each other but those marked as/branded Chemicon are probably built to better standards using Japanese aluminum. (Or at least I like to think so...)

25v 470mf Sam Young LXZ - 10x16mm - Ripple=1050, ESR=0.068
Panasonic FC, Digikey PN: P10275-ND .. Ripple=1050, ESR=0.068

50v 22mf Sam Young - [What series? Can't look up.]
Panasonic FC should be fine here anyway.
Panasonic FC, Digikey PN: P10318-ND

CapXon seem to do okay in power supplies but not in other low ESR applications. These aren't low ESR rated caps though.

16v 100mf CapXon KM 105c
- 6.3x11mm - Ripple=130, [GP cap, ESR not listed]
- 5x11mm - Ripple=115, [GP cap, ESR not listed]
If 6.3x11mm: Panasonic FC, Digikey PN: P11198-ND .. Ripple=290
If 5x11mm: Nichicon VZ, Digikey PN: 493-1283-ND .. Ripple=115

.

[PCBONEZ]

Re: Samsung Syncmaster 173s Input signal problem

OH, AND:
Monitors are not Hot-Swap.
You need to turn them and the PC off BEFORE you plug VGA cables in or unplug them.

.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

Well. I suppose you are right about the voltage, but I was (and still I am) sure it was the BLON for the lamp. And it was/is. But the result was the same : no data on screen, blinking (green) led and lamps on (the only change).
On the Video board (the other one in there), I checked four surface mounted caps (2 are 47 16v and 2 are 100 16v. I assume the 47 and 100 are mf) and one of the two 100 16v showed no resistance (as if it was a fuse) and the other did not.The one in short was right before the output of the BLON, so I removed it and put one normal cap, but the same result showed up. Then I removed the other 100 16v and swapped them, putting one in the other's place and viceversa. Same result. I noticed that the one that was "short" had one loose pin
Now the lamps are always on, even if I turn off the monitor using the power button (I did not leave the temp voltage bridge used to test, and I'm sure the pins are not in short). I tried doing all of this with and without the LCD panel attached with the ribbon cable to the video board, and same result. I am pretty sure now that the problem is in the video board section. I browsed in www_fixya_com, and someone suggested that I pushed down the chip (eeprom, I think), and it was kind of loose, but no change. Now I removed completely the video board to check it more in detail, but I think that it is dead.

I have a question : can you replace the surface mount caps with thru hole ones? or what is the difference?

And thanks for the advise so far.

[PCBONEZ]

Re: Samsung Syncmaster 173s Input signal problem

I had a viewsonic with the blinking green light problem and it only actually needed one cap. It would probably be the same (functionally) as your 25v 470mf. It was an output filter cap between the PSU section and the video section.
- Mine was obvious though because it was bloated.
.

[PCBONEZ]

Re: Samsung Syncmaster 173s Input signal problem

>> replace the surface mount caps <<
Not easily but I've seen people do it.
Functionally the caps are no different if the specs are the same.
If you try that make sure you don't damage the bung (plug) in the bottom of the cap when you are bending leads around or it will leak. Best to grab lead with a mini-needle-nose pliers placed right next to the bung and bend against the pliers.
Also don't short leads to sides of can.
.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

I'll change the 25v cap and try to change the surface mount ones. I think it is dead already and I'm only counting with the rest of the components for future use, so nothing will be lost.

[kc8adu]

Re: Samsung Syncmaster 173s Input signal problem

i see the guts of these in industrial touchscreens and the sm lytics dry out in a few years.replace them ALL.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

The SM were changed yesterday but same result. One of them was bad anyway (a loose leg). I have just changed the 25v 470mf Sam Young for a Rubycon, and there was image (dim because the original lamps were used in another monitor and I installed two lamps for the inverter to work : one inside the panel , and one that doe snot fit is outside. Lit but outside) .

Now the lamps don't turn off (since I changed the SM on the video board). The line that I think (now I'm sure) is BLON before the change didn't have any voltage with the monitor in off mode, and now it has between 1.9 and 2.3v, which causes the lamps to ignite.
Any idea? This started to happen when the SM were changed.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

So far the monitor still works like a dream.....just the lamps never turn off. If I turn off the monitor via the on/off button, the green led turns off and the image fades to end up in an all white screen. I have to disconnect the power cable to shut it off. Well, I think it's better that way than the way I got it. In the end, it was only the 25v 470mf output cap that PCBONEZ mentioned. The other two changed caps didn't do anything (better, I mean..), except that maybe I shorted one and that's why the voltage leaks and the lamps are always on.

Thanks for all your help.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

I just noted that between the 2 pins of one of the 150mf caps I changed (that when I followed the track, ended up in the pin that I am sure is the 5v BLON signal) there's always 4.9~5.0v. The other one that I changed does not (this other one has only voltage when the LCD Panel turns on, and goes to one of the pins from Video Board to the LCD). I think this is the reason for the lamps to be always lit.

[EGuevarae]

Re: Samsung Syncmaster 173s Input signal problem

Well, one of the lamps (lower pair) blow... literally. With bang and all. I gave up and used the screen to fix a Dell E171FP that came to me with an all-white screen. The monitor is now working perfectly : Dell's original circuitry (with replaced CapXons) and lamps (all four) and Samsung 173s LCD panel.
I'll just store the parts of the 173s to be used in the future. I couldn't win this one ....

[Bobdee]

Re: Samsung Syncmaster 173s Input signal problem

Hello eguevarae
Enjoyed the Thread with all your Info, and Perceiverence, and enthusiasm,
AS with the contributions from the others,
THXs bob

(edit) sorry cancell edit

[Wizard]

Re: Samsung Syncmaster 173s Input signal problem

Wow. Bang! :O

Well, there is a bulletin on that 173 series that there is a ferrite SMD inductor next to the power plug on the green mainboard, take this out and bridge this with little piece of wire and solder. Then replace many SMD electrolytic capacitors.

Cheers, Wizard