Samsung 901B S finds no input signal

[teslacap]

Hallo there,

after repairing the inverter-board of a Samsung 901B S, there is still a problem
with the input signal. Even though a signal is connected to the VGA-SUB15, the monitor toggles between digital and analog input (screen-window) and doesn't process the signal onto the screen. Therefore I guess something on the VGA board is damaged too. Does anybody know this bug?

[momaka]

Re: Samsung 901B S finds no input signal

Could be a bad joint on the VGA connector of your video/logic board.
Could be bad capacitors on the video/logic board or a bad regulator.
Could also be corrupt firmware.

The first 2 items are fixable, so start by checking the joints on the VGA connector and make sure all of the linear regulators are outputting the correct voltage. If yes, proceed by replacing the electrolytic caps on the video/logic board. If that doesn't work, it's possible the firmware is corrupted.

Post some pictures of the video/logic board so we can see what we are working with. Please attach pictures using the hosting service on this website (when posting, use Advanced mode - below the text box, you will see a button "Manage Attachments") and make sure your pictures are large and clear enough (yet not larger than 2000x2000 since that won't upload).

[teslacap]

Re: Samsung 901B S finds no input signal

Hallo momaka,

thank you for your reply. I checked the pins from SUB-D and resoldered
it. After I checked the voltage over each visible capacitor (have no schematic)
and wrote the values on it (see picture). Also I tried the pin5/pin6 method
(bridged with 50 Ohms) on the Novatek IC. Surprising was the changing of sceen
message after. Instead of toggeling between analog and digital there appears
"you use the wrong resolution, try 1280x1024 60Hz". That's quite telling.
I'm not quite shure if this capacitor above, with 0.00V shows it's normal value.
Without a schematic difficult to say. If used only as galvanic isolator,
this value might be normal, but never when should be a regulator cap. In
this case either a voltage is missing or the cap is probably shorted.

If possibility nr. 3 is the reason for this bug, it will be gainless
to buy another vga-board for about 47.- Euros. The value of this monitor
is marginally lower.

[selldoor]

Re: Samsung 901B S finds no input signal

Is this brown spot ok?

[jetadm123]

Re: Samsung 901B S finds no input signal

The Novatek controller chip was used on several different models of Samsung monitors. From what I understand, the chip goes bad over time and can cause the problems you're seeing. The only solution is to replace the Novatek chip and reload it's firmware. See the link for the schematic for the Samsung 912N model with similar logic board (vga only):


https://www.badcaps.net/forum/showth...hlight=novatek


Also, the resistor trick will eventually cause the chip to burn out.

Repair success for the logic board are poor.

[momaka]

Re: Samsung 901B S finds no input signal

I'm not quite shure if this capacitor above, with 0.00V shows it's normal value.
Without a schematic difficult to say. If used only as galvanic isolator,
this value might be normal, but never when should be a regulator cap. In
this case either a voltage is missing or the cap is probably shorted.

Yes, a cap that big without any voltage across it doesn't look normal.

What's the part number of IC600? See if any of the pins of IC600 connect to the (+) side of that cap.

The dark spot that selldoor found looks suspicious as well.

[budm]

Re: Samsung 901B S finds no input signal

I think that the DC filter cap after the switched transistor for supplying B+ to the T-CON board, when it has no video signal, the transistor is turn off, the main board also tells the Backlights to turn off at the same time (go into standby mode to save power). Check the voltage again when you have Video signal.

[teslacap]

Re: Samsung 901B S finds no input signal

Good evening @all,

@selldoor: this brown spot was only color. I cleaned it away with a little alkohol
(of course not inside me, but onto the platine-surface)

@jetadmin, momaka, budm: I will go on with the monitor when I have enough time left to do. In the moment I'm tired, because a lot of other important things needed to be done today. Thanks for your inspiring tips. I will check asap.

[teslacap]

Re: Samsung 901B S finds no input signal

Hallo,

after switching on I got a voltage over the 0,00V Cap from about
4,92V during for the same time this window-frame appears, where
analog oder digital input is toggling. After around 20s the signal
breaks down to 0,00V. I think I will need a second-hand video board.

Cheers

[selldoor]

Re: Samsung 901B S finds no input signal

I am struggling to follow this.
I didnt understand what you meant in the first post by:
"the monitor toggles between digital and analog input (screen-window) and doesn't process the signal onto the screen."
and you use a similar reference in the last post:
"where analog oder digital input is toggling."

Can you say that differently at all? ( I do understand "oder")

You may need a new video board but I am not certain we have bottomed out the voltages from the Power supply.

If you want to do that can you post a picture of the top and bottom of the power supply and of the inverter if a separate board.

[momaka]

Re: Samsung 901B S finds no input signal

after switching on I got a voltage over the 0,00V Cap from about 4,92V during for the same time this window-frame appears, where analog oder digital input is toggling. After around 20s the signal breaks down to 0,00V.

That looks normal. The 4.92V you're seeing is likely going to the t-con board, so when the monitor stops toggling between analog and digital inputs, it turns off the backlight and the t-con board. So I would say the voltage on that cap is not your problem

I am struggling to follow this.
I didnt understand what you meant in the first post by:
"the monitor toggles between digital and analog input (screen-window) and doesn't process the signal onto the screen."
and you use a similar reference in the last post:
"where analog oder digital input is toggling."

On some monitors with DVI and VGA inputs, the monitor will keep trying to look for a signal on both of these inputs (and hence "toggle" between looking for input on VGA and looking for input on DVI).

You may need a new video board but I am not certain we have bottomed out the voltages from the Power supply.

If you want to do that can you post a picture of the top and bottom of the power supply and of the inverter if a separate board.

If it was a power supply/inverter issue, most of the time the monitor won't power on at all. So it's probably the video board that's causing this.

[selldoor]

Re: Samsung 901B S finds no input signal

Thanks Momaka - probably not relevant but have you any idea what the component
marked FT600 might be - not a description I have come across before.

@teslacap - have you tried it with a DVI cable?

[Rtech]

Re: Samsung 901B S finds no input signal

There is normally quite a few Ferrite Beads on Monitor boards(FB).as this is the only 'F' designator I can see ?? then suspect that is what it is..WHAT the 'T' stands for I cannot think .

[momaka]

Re: Samsung 901B S finds no input signal

Thanks Momaka - probably not relevant but have you any idea what the component
marked FT600 might be - not a description I have come across before.

You're welcome.
I'm not sure what FT stands for. As Rtech mentioned, FB usually stands for Ferrite Bead and F by itself stands for Fuse.
From my past observation and experience, SMD ferrite beads were *usually* gray or dark gray in color (although I've noticed that in rare cases, some SMD ceramic caps were gray as well so care should be taken not to confuse them). Judging by the picture, FT600 is most likely a ferrite bead/inductor.