Samsung 933SN - 2sec on, then off

[stj]

Re: Samsung 933SN - 2sec on, then off

check your soldering and that all the caps are in the right way around.

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Wellp .. it just flat out won't turn on now. I replaced all the caps, put it all back together .. no power.

Meh, I got it at Goodwill a year and a half ago for cheap. And it had some small bruises on the screen. It was a good experience.

On the plus side, I picked up a 19in HP w19b (PN: P87740AA) 1440x900 at Goodwill for $9.95 and works great!

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Well, I ordered Panny FM replacement caps from Mouser, they should be here in a few days. I'll report back when it's all be recapped.

[gurhy]

Re: Samsung 933SN - 2sec on, then off

I have the same monitor and have exactly the same problem, turns out this model is common for going wrong like this. 1 of my surface mounts had fell off which caused other issues but now installed the monitor works apart from that same issue.

more to a description, the monitor lights up and powers on perfectly fine tad slow on start up, this is just wth power lead, as soon as I add the vga cable the monitor shuts off, bare in mind that's before connecting to the pc, as soon as I connect to my pc the screen then shows my desktop for a second then go's out. some times the led will blink and to me that makes me assume there is a power failure some where :s

[nomoresonys]

Re: Samsung 933SN - 2sec on, then off

well, start by testing the connector on power supply for expected voltages, theres a label with expected voltages right by it, do you have a digital mutimeter?

[budm]

Re: Samsung 933SN - 2sec on, then off

So you do have 2-second to black, as momaka had indicated the possibilities in post 7.

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

Sorry I wasn't more specific/descriptive on my issue. The monitor would turn on for 2 sec or less, and then the image would turn black, but the power LED would still be on.

[momaka]

Re: Samsung 933SN - 2sec on, then off

Thanks, should I replace all caps, even the huge 450v 68uF?

No, that one doesn't need to be replaced. It almost never causes problems in PSUs like these. And they tend to be pricey.
(Now, if the PSU did have APFC, I would have suggested a replacement... but that's not the case here).

Oh, what about the two black Dioes, should those be replaced also?

No.
PSU would not stay with power ON even for a fraction of second if one of them was bad.

Now here is my question to you: Your title says: "2sec on, then off". What do you mean by "off"? Does the image on the monitor turn OFF *only* (with the LED on the monitor still indicating the monitor is ON), -or- does the monitor turn OFF entirely (i.e. no lights or LEDs on the monitor at all).

If it's issue #1 above, then you probably have an inverter problem (i.e. bad CCFLs/CCFL wires, bad inverter transformer(s), and/or possibly bad caps on the inverter rail)

If it's issue #2, then the problem is usually either bad caps in the power supply (likely) or bad inverter drivers (MOSFETs or BJTs).

[mariushm]

Re: Samsung 933SN - 2sec on, then off

The number starting with E is an UL registration code, it probably belongs to the company that manufactured the circuit board, which could be different or the same company that put the components on the circuit boards.

It doesn't give you much information.

If the capacitors on the board look good... it could be that the capacitors are bad even if they look good but I'm inclined more into checking the fluorescent tubes that are powered by the board.

The monitor has 2 or 4 fluorescent tubes (very small in diameter) which work at high voltage (750-1400 volts) and low current (a few mA).

There are a few problems with such fluorescent tubes:

The wire at the end of those tubes can become loose or have an intermittent contact, which will make the controller on the board stop the lamps after a few seconds. You can check for that by gently pulling away the soft rubber/plastic ends and inspecting the solder there and how well the wire is attached.
When you're done, the cap will have to be back in place otherwise there will be arc-ing between the solder and the metal backing of the lcd screen.

The fluorescent tubes can also simply be too old. As they age (with lots of hours of operation), the tubes will consume more power to operate. Above a certain threshold of power consumption, the controller will detect more current than normal is used and stops the whole circuit for safety reasons.
For example, the transformer used to boost low voltage to 700-1500v is only designed for a few mA and if the lamps use more it would overheat, get damaged and potentially make the monitor unsafe.
The electric arcs like in the previous example are detected as higher power consumption also, so it makes sense to shut off the circuit for protection in such situation.

So check the fluorescent tubes before buying another board or capacitors.

[angel-boy]

Re: Samsung 933SN - 2sec on, then off

only caps, should resolve the problem.

[Joshatdot]

Re: Samsung 933SN - 2sec on, then off

dry capacitors, try to change it

Thanks, should I replace all caps, even the huge 450v 68uF? or just the smaller ones: 10v 220uF, 25v 47uF, and 25v 470uF. I'll be getting Panasonic FMs.

Oh, what about the two black Dioes, should those be replaced also?

[nomoresonys]

Re: Samsung 933SN - 2sec on, then off

ok, nice start, now we need more pics. of each board and one of the whole back to see how theyr all connected.

[angel-boy]

Re: Samsung 933SN - 2sec on, then off

dry capacitors, try to change it

[Joshatdot]

I've searched & read many a post about related 'monitor is on for 2 seconds, than goes off'. I did not see much related to my monitor, Samsung 933SN.

The power supply board says "E131175" and it seems to be common to many different monitors: Dell, Samsung, Acer, Sanyo, Acer, Gateway.

I could not find any evidence saying stuff like "replace CAP this and that", or summat. I could replace the PSU board, for $10 to $40, but from what I can see on eBay, they are not 100% looking like my board.

I do not see any baked/cooked components on the PCB, the CAPs do not looks bulging, the soldering looks fairly clean too.