Samsung 2693HM. it operates and suddenly switches off

[alfanikos]

I do own a Samsung 2693HM. For more than 5 years it served me without any problem. for the last month it has the following problem:

1. Connect monitor to computer
2. Turn on - blue light stays lit
3. Desktop shows up, operates without any problem
4. Suddenly it turns off. It makes a noise from the computer speakers (like a spark) when it switches off
5. The blue light goes off
6. it like dead. Even if you switch is off from the rear switch or unplug it from both the computer and the mains and re-plug it stays switch off.
7. You leave it plugged and after awhile it recovers. Blue light goes on. Screen works like a charm (like never happened anything).
8. It can stay on for week (or more) and then randomly off again.

I took it to Samsung Service and they have test it for almost two weeks in operation. No problem at All. In never switched off.

They opened it and checked an said that they found nothing wrong. But of course since the problem has not presented they cannot identify the cause.

I took it home used it for a month and then suddenly OFF.

I opened it and changed some electrolytic capacitors in the power supply unit , checked the voltages, everything seemed OK.

Checked all the connectors and the lower part of the invertor board for cold or cracked solders. No findings.

Disconnected the lamps (considering that they draw additional current leading the driving fets power down), voltages were OK.

Any one has faced a similar problem or even better has found the cause of the problem and repaired it?

Any suggestions?

The strange thing is that it switches off suddenly (blue light also off) and then suddenly On. No particular duration of OFF or ON condition. It seems that you have to unplug it from the computer to reset and switch on again

[RJARRRPCGP]

Re: Samsung 2693HM. it operates and suddenly switches off

Try a reflow of the power connectors.

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

You appear to have covered all bases these are the worst type of problem.
If the blue light is off it suggests there is no power at all. Did you do any tests after it went off but still plugged in?. Even just a test on the BIG cap would be useful.
Is it plugged direct into a mains socket - no surge protector or extension?

[Ramee]

Re: Samsung 2693HM. it operates and suddenly switches off

Check the fuse, transistor and those diodes on the heatsink.

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

RJARRRPCGP
If it was the power connector then by moving the plug it should restore back. This is not happening, Anyway I will check it.

Rammee
Can you be more specific as of which diodes you are talking about?

As of fuses which one are you talking? These should be of the type that cut the power and after a while are restored back to normal because Screen operates suddelny stops and then restors back.

Can you indicate on the photo (mark)?

Furthermore I have to say tat I have not changed all the electrolitic capacitors and this because the ones that I have taken one (and even change) have been measured and they were within the 10% of the value.

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

Did you do any tests after it went off but still plugged in?. Even just a test on the BIG cap would be useful.
Is it plugged direct into a mains socket - no surge protector or extension?

?

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

selldoor

good question.

A. I have check the voltages after it went off but still plugged in and they seemed OK. Anyway I will do it again, but the issue is that I cannot simulate the "powering off". Have the screen fully dismantled and awating to power off. Normally when it is dismantled I cannot feet it with computer signal. Will try and revert.

B. Big capacitor has not been checked. It has to be removed and repalaced. I can still measure it but I will revert with findings.

C. No it is not plugged directly to the mains and this is something that I am suspecting to be the culprit. The screen is plugged in an online Eaton UPS. it seems that the "powering off" issue started a couple of months ago when I changed the UPS (from a normal type to an online one). Previously I was using a normal APC UPS. I am suspecting that and I will connect the Screen directly to the mains. Possibly this is the reason that Samsung Service has not observed anything even if it was for two weeks in operation at their bench. Will do the test and revert.

In all cases even if the frequency fed(bythe on line UPS) is not the correct one, why the other screen (a Samsung T260 HD) connected (two screens are connected to the same computer VGA card) is not powering off (even the computer).

Furthermore Screen is fed by DVI cable (gigital) not the analogue one.

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

Now it failed totaly.

No blue led lid at all

Checked the voltages nothing.

There is only power in the primary of the power supply.

No secondary voltages at all (5.3 volt, 18 volt, or 24 volt)

Anyone can assist?.

Can anyone provide the schematic diagram BN44-00181B or PSLF131501A

[budm]

Re: Samsung 2693HM. it operates and suddenly switches off

So what Voltage do you have on that big main filter cap on the primary side?
Can you provide good clear pictures of the whole both sides of the power supply board, and also in sections so I can clearly see the traces on the board?

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

Voltage at the main filter Capacitor is 323 Volts (Our mains he is 220Volts)

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

and photos are continuing

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

OK in Pic 2 post10 to the right of the BIG cap there is a small red rectangular box.
That is a fuse - can you test it. POWER OFF meter on ohms 200 one probe to each side.

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

Have tested the fuse

It is OK 0 Ohms with probes to each side

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

OK If the board is connected can you test the voltage on each side of the fuse with respect to a Primary ground. (negative leg on BIG cap)
If the board is out can you resolder Qm812 and Qm813 joints dont look good on picture

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

Sorry - see edit on previous post

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

Board is out.

Have re-soldered QM812 and QM813 It is written on them "K3561". have tested them (actually compared them) with OHMETER (selection of Diode) and both give identical measurements.

One side of Fuse and (negative leg of big Cap) voltage 323 Volts
Second Side of Fuse and (negative leg of big Cap) voltage 323 Volts

[selldoor]

Re: Samsung 2693HM. it operates and suddenly switches off

Are you sure it was switched on when you tested the secondary voltages
I ask as it has happened a few times before.

[alfanikos]

Re: Samsung 2693HM. it operates and suddenly switches off

This screen has a touch switch. When you touch it the blue led goes on (start blinking). when there is signal from the computer it stops blinking and it stays blue.

Currently there is no blue light either blinking of steady irrespective if you touch the switch (slide your finger above the ON Position)

There should be a standby voltage that is always ON. When you touch the switch then it senses that you want to turn on the screen and gives the order to the power supply to start.

Now there is no standby power at all.

See Photo 9 on Post #10

[kiasfo]

Re: Samsung 2693HM. it operates and suddenly switches off

i have exactly the same problem with you,turning off randomly and now not power at all.did you find any solution?