Samsung Synchmaster 2693HM WHITE SCREEN

[Chris02]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Everything about my fix of 2693HM you can find in this thread

OncleOh asked me if I can measure the testpoint from my working t-con board. Here are the calues of the working one.

Name of Testpoint Voltage / Resistance to GND
VDDG 27V / 100k
VEEG -7V / 41,5k
VDDA 13V / ~5,5k (it seems that the TP is connected to any C which charged while measuring)


I hope it will help anyone to fix much more 2693hm!


Regards from Germany
Chris

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
will check all the caps and let you know.
Thanks for now.

Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

The voltages are right.
My only guess would be if the video signals are somehow not getting to the t-con board or if the video/logic board is not sending any. That's a bit above my level of troubleshooting expertise, though.
Perhaps just check the other small ceramic caps for short circuit. If none, I don't know what else to suggest.

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Hi,
i took a look at the pdf and the VEEG in -V so the T-con is ok.
Why then white screen?

Regards!
Leo

@momaka
yes the VEEG is -7V, is these ok or wrong?

Regards!
Leo

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
yes the VEEG is -7V, is these ok or wrong?

Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Those readings seem good. Not sure what's wrong with the t-con then (if anything).
Just out of curiosity - was VEEG 7V or -7V when you measured it?

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Sorry for too long delay.
Here are the readings:
VDDA 5,9K / 13,12V
VDDO 1,5k / 3,3V
VEEG 41k / 7V
VDDG 100k / 27,4V

Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

I already measured the resistances between the testpoint and their voltages:

VEEG 41,8k / 0,385V
VDDG 304 / 0V
VDDD 141 / 3,325V
VDDA 5,7k / 0V

5V supply voltage is ok.

Resistances seem okay, but the voltages for VDDA, VDDG, and VEEG are all gone. Without VDDA, VDDG and VEEG won't come on either.
Measure the resistance for all of the small ceramic capacitors to the right of IC301 and IC302 (those RAM chips).
Since your board my be slightly different, it is advisable to post some pictures of your board. At this point, I would say open a new thread, just so that we don't confuse which member had which problem with their t-con.

[Chris02]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Hi!

I hope that it is ok, that I'll post with my Problem in this thread too. If not tell me and I'll opend a new one.

I have got a 2693HM which starts only with a white screen. I knew before I read this thread, that my fault comes from T-CON board.

I already measured the resistances between the testpoint and their voltages:

VEEG 41,8k / 0,385V
VDDG 304 / 0V
VDDD 141 / 3,325V
VDDA 5,7k / 0V

5V supply voltage is ok.

And I can't find any blown tracks on the PCB.

I hope you have got also some tipps for me and we three can fix both monitors!

Regards
Chris

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Yes they look okay to me as well.

Next, measure the voltages on these rails. For ground, you can use any metal part of the monitor's case.

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Sory for the delay,
here are the reading but think they are ok:
VDDA 5,9k
VDDO 1,5k
VEEG 41k
VDDG 100k

Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
at VEEG and VDDG i got 0, no reading at all.

0 (zero) and no reading are NOT the same thing!

Most multimeters will show "OL" or a "1" on the left side of the screen if you set them to measure resistance and you leave the probes not connected to anything. The "OL"/"1" means "out-of-range" reading. On the resistance setting of a multimeter, this means that the resistance you're trying to measure is higher than the scale you selected. So for example, if you have a manual multimeter and you set it to measure a resistor on the 200 Ohm scale but the resistor is 400 Ohms, then the multimeter will show that "OL"/"1" reading.
A zero on the other hand, as in 0.00 Ohms, means short circuit.

Do this test for me... set your multimeter on the lowest resistance setting (only if it is a manual one, of course) and touch both probes together. The resistance you get for that setting is the SHORT-CIRCUIT resistance for your multimeter. Whenever you get this reading at this scale on your multimeter, then that's when you have a short circuit or a very low resistance. Good multimeters will show around 0.6 to 0.8 Ohms. Cheap ones will show around 1 or 2 Ohms.

Now check VEEG and VDDG using the lowest resistance setting on your multimeter and tell me what you get.

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
at VEEG and VDDG i got 0, no reading at all.

Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Hi,
finaly managed to get the readings, used autorange multimeter set to kilo, and all ok except VDDA reads 5,90K.

5.9 kOhms (5900 Ohms) is actually fine. It's the low resistances (in the 10's of Ohms) that we are looking for as those usually indicate a problem. Like I mentioned, disregard any resistances *above* 2000 Ohms (2 kOhms).

What resistances did you get for VEEG and VDDG?

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

Hi,
finaly managed to get the readings, used autorange multimeter set to kilo, and all ok except VDDA reads 5,90K.
Have to get another multimeter and repeat the measurments.

Regards!
Leo

[PlainBill]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
Hi,
will check and let you know,

@PlainBill
which photos do you need?


Regards!
Leo

None. momaka has specified a process that should identify the problem.

PlainBill

[OncleOh]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

@momaka
Hi,
will check and let you know,

@PlainBill
which photos do you need?


Regards!
Leo

[momaka]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

So what do you suggest about t-con board?

Short version:
Using the picture in post #8 as a reference (this one), first find the 3 test points AVDD, VEEG, and VDDG.
AVDD is located under the bank of ceramic capacitors under the round inductor.
VEEG and VDDG are located all the way on the right side of the t-con where the "260WU01C" and other board numbers are.

Once you find those test points, measure the resistance of each to ground. If you have a manual multimeter, use the 2000 Ohm scale. If you have an auto multimeter, disregard any readings above 2000 Ohms.

Basically we are looking for a short circuit or very low resistance on these test points. If any of them measure less than 200 Ohms, post what resistance you got here. I consider anything under 100 Ohms as suspicious, 30 Ohms or less as highly suspicious, and 10 Ohms or less a very likely short circuit.

Also, check the ceramic capacitors around D502, Q503, and Q504, and D504 for short circuit/ low resistance. To do that, just measure the resistance across them. If you find any of them to show under 100 Ohms, let me know which ones.


Long Version (only for those interested in more info on this t-con board:

Background
There are 4 important voltage rails on a t-con board:
- the main supply rail, which is usually 5v
- the main step-up (boosted) voltage rail, usually 9 to 13v (derived from the main supply/ 5v). For this t-con board, test point AVDD is directly connected to this voltage rail.
- two secondary step-up rails (derived from main step-up) for turning the transistors in the TFT ON and OFF. For this t-con, test points VEEG and VDDG are directly connected to these rails.

A white screen problem usually happens if either the t-con is not receiving power (main supply rail not present) or one of the TFT voltage rails (the step-up rails) on the t-con board has a fault. The fact that the screen fades to black after being white suggests that the main step-up is working but one of the secondary ones isn't.

More often than not, the cause for this is a shorted ceramic capacitor on one of those rails. And that's what we're going to look for. Of course, first those rails need to be found on the t-con board.

Let's start with the picture of the t-con on post #8.
The round inductor is always easiest to spot (IMO). This inductor is part of the main step-up voltage rail. Once located, the secondary step-up rails can be usually found close by. Next, we find the controller that produces these rails. For this particular t-con, the controller is a MAX8795A "smart" IC from MAXIM. Data sheet here:

A basic sample circuit diagram is given on page 1, and a more elaborate one on page 15. Page 13 has a table that describes the functions of each pin on the controller.

In many cases, the circuit on the t-con will closely resemble the sample circuits given in the data sheet. In the data sheet above, the t-con TFT rails are referred to as Vmain (for AVDD), V_GOFF (for VEEG), and V_GON (for VDDG).

As can be seen from the sample circuits in the data sheet, these rails have caps connected to them for filtering. Normally, the t-con board uses ceramic caps for these. The problem is that ceramic caps like to short circuit when they fail, so when one of them fails, it brings down the whole TFT power supply section.

All one has to do is follow the sample circuits in the data sheet and then try to determine the corresponding components on their t-con board. This is useful for checking resistances.

[PlainBill]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

hello all
was looking back on the first post and oncleOh said

(Hi i have a samsung 2693HM with white screen WHEN it POWERS OFF

I remember on the old Benq boards the INVERTER transistors and sometimes the FU90?? mosfets use to fail,
if you replaced the transistors and had not spotted one of the FU90?? mofets had failed,
then the monitor would work but when you powered off, the screen would stay on with a white screen untill you removed AC
dont know if this applies to this monitors inverter in some way, but thought I would mention this as it may help those of you who do know

Good catch. Most monitors in this size turn off the main power supply and the inverter, but better pictures would be required before I could be sure of that.

Edit: that appears to be the case here. That would imply either a short on the power supply, or a problem on the signal card.

PlainBill

[trebo]

Re: Samsung Synchmaster 2693HM WHITE SCREEN

hello all
was looking back on the first post and oncleOh said

(Hi i have a samsung 2693HM with white screen WHEN it POWERS OFF

I remember on the old Benq boards the INVERTER transistors and sometimes the FU90?? mosfets use to fail,
if you replaced the transistors and had not spotted one of the FU90?? mofets had failed,
then the monitor would work but when you powered off, the screen would stay on with a white screen untill you removed AC
dont know if this applies to this monitors inverter in some way, but thought I would mention this as it may help those of you who do know