Asus VH242H: 2 seconds to black..

[Buhrmester]

So I have been spending the last 24 hours trying to figure out how to fix my monitor instead of having to buy a new one. I have done a little research, but need some clarification on things. Keep in mind, this is all very new to me and I am learning as I go. I have some experience with electricity and circuit boards from growing up, but I have forgotten most of it.

The symptoms -

When I turn my monitor on, it shows a great picture for 2 seconds and then the backlight goes out. It does this over and over again. I am able to see the screen when I shine a light on it, so it is obviously power/light.

What I have done -

1. I first tried turning the brightness down as some have said this helps. This didn't work for me.

2. I have taken the monitor apart and have removed and or tested the electrolytic capacitors and all seem to be reading at their expected level.

3. I put the power board back together and into the shell of the monitor and plugged it in and made it a live circuit, without the screen hooked up. I tested the voltage at various places and found that at the connections for the screen cables, the voltage spikes from 0V to anywhere between 20-30V when I start the monitor (or change inputs) and then drops back to 0V after 2 seconds. So I think it is safe to assume that there is a problem on my board and this is why the backlight is going out.

My questions -

Can capacitors see a voltage drop? I notice some of the ceramic capacitors drop the voltage from 120V to 0V or 68V to 0V in various places. I tested some of them and they seemed normal, so I assume this normal in a live circuit.

The reason I ask this is because I tried tracing the power backwards from the cable connections, while turning the power on or switching inputs, and noticed that one of the electrolytic capacitors was fluctuating from 0V to 3V on its positive side, but was showing nothing on its negative side. So with my limited knowledge, that made me think that the power is not getting through. However, the reason I am doubtful is because I checked the capacitance of this particular one out of circuit and it seemed fine. Does this make sense? Is this possible?

In the pic -

The BLUE boxes are ceramic capacitors that see a drops to 0V. Top top one 68V to 0V and the bottom left one 120V to 0V.

The RED box is the electroyltic capacitor that fluctuates from 0V to 3V on the positive side, but sees no voltage on the other side.

The YELLOW boxes are the transformers, each pin sees the spike when the monitor is initially turned on, but then drops to 0V

The WHITE boxes are where the connections for the backlight cables are and see the spike to 20V+ when the monitor is initially turned on.

Any help is greatly appreciated.

[budm]

Re: Asus VH242H: 2 seconds to black..

"The BLUE boxes are ceramic capacitors that see a drops to 0V. Top top one 68V to 0V and the bottom left one 120V to 0V. " That the hot side of the circuit, you cannot use chassis or Safety ground as the ground ref point. Those caps will not affect the function of the unit so do not worry about it for now.
"The RED box is the electrolytic capacitor" That is part of the inverter circuit, may be for output coupling.
"The YELLOW boxes are the transformers" those are inverter primary side of the transformer winding.
"The WHITE boxes are where the connections for the backlight" those are high voltage out put, the start-up voltage cab be as high as 2000VAC, so do not try to use your meter to measure it, you can damage in the meter input circuits.
So post the pictures of the top side of the board also.
Check the voltage between those two points as shown in the picture.
Since you do have 2 seconds to black problem, then please read the 2-second to black guide.
https://www.badcaps.net/forum/showthread.php?t=10419

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

When I have the multimeter touching nothing but air I get a reading of 0.06V

In the first pic-
The YELLOW box has everything at 68V.
The RED box has everything 0.03V, including the WHITE boxes that I just tested, but those two points you asked me to test jump to 0.5V when I switch inputs, and then after 2 seconds drop back down.
I noticed in the BLUE boxes there was a constant voltage of about 0.5V and it would drop to 2.5V when the monitor would change input.

The other 3 pics are of the top of the board.

Thank you and I appreciated all the help!!

[budm]

Re: Asus VH242H: 2 seconds to black..

The DC voltage at the two point I have you check is the power supply voltage for the inverter circuit, it should be around 16~20vdc WITHOUT turning on the monitor. The power supply is an always on power supply, it will put out voltages the miniute you apply 120Vac to it.
So if you are only getting 0.5V, the power supply is not working or it is in safety shutdown mode.
Next test will be resistance test on those two points without AC power to the unit.

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

The DC voltage at the two point I have you check is the power supply voltage for the inverter circuit, it should be around 16~20vdc WITHOUT turning on the monitor. The power supply is an always on power supply, it will put out voltages the miniute you apply 120Vac to it.
So if you are only getting 0.5V, the power supply is not working or it is in safety shutdown mode.
Next test will be resistance test on those two points without AC power to the unit.

Ok, I made a mistake while measuring it. I was measuring vac. The WHITE rectangle box on the right is reading 17vdc while powered off put plugged in, and the little square WHITE box is reading 0vdc while powered off but plugged in. As a side note, I am not sure if it matters, but on the other side of the board, there is nothing soldered into the A2 point (the left point you had me test).

I am fairly new to this. So I wasn't sure if I was testing the resistance correctly. But the resistance between the two points that you labeled, is reading as OL (I put the positive tester on one point, and the negative tester on the other). I also measured the resistance of the the two points in the WHITE rectangle and they measured 0.1ohms.

Let me know if I am doing it right.

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

Ignore what I just said. The DC voltage between the two points you asked me to measure is 17vdc

[budm]

Re: Asus VH242H: 2 seconds to black..

"the left point you had me test" that big trace is the Ground ref. for the secondary side (cold).
So the inverter is getting the B+ OK.
2-second to black can be caused by bad MOSFET (there are two 8-pin SMD MOSFETs in that section, P/N?), inverter transformer, lamps, etc.
BTW: I cannot clearly read the P/N as printed on the top of the inverter transformer, can you tell me what the numbers are?

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

9945N AABY05 on both.

Also I have a new problem. I was reading the 2 second to black guide thread and was going to test CCFLs (without a spare). When I put the monitor partially back together to test them, I plugged it in and the power button doesn't work. The LED does not light up when I click power on, and the monitor does not turn on. I think unhooked everything and hooked it back up again without the LCD screen (like I had it before when I was testing) and I can't seem to get the power button to work again. The inverter board still reads all the proper vdc everywhere.

I did make sure I put the connections in the right spot when I tried hooking the monitor back up. Any idea?

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

Correction. Now the vdc in those two spots reads 2-3vdc. Did i just break that damn thing?

[budm]

Re: Asus VH242H: 2 seconds to black..

OK, run the power supply board by itself without the logic board connected to see if the power supply will power up.

[Buhrmester]

Re: Asus VH242H: 2 seconds to black..

Power supply board by itself sees 3.5vdc at those two spots.

[stevwills]

Re: Asus VH242H: 2 seconds to black..

hey I also have the same problem with my asus vh242 monitor Could you Guys Help me figure it out? i am pretty good when it comes to troubleshooting computers. but for me monitors are a Different world, i Do not know much about electronics. this being said mine also does a 2 seconds to black, but when i shine a light on it, there is no image that shows up. the sound works. iv'e completely disassembled the monitor and i don't see any bad caps.

when I plug both backlights in, they do not light up instantly, they both light up like a loading screen (at the same pace) if I plug one in, it Lights up less than when i plug them all in.

here i am trying to troubleshoot the monitor as if it was a PC. XD could you guys Guide me throught the steps plz . I do have a multimetre. I have read the posts above, I'm quite a newb. but Im determined to fix it and get a free monitor, cause it was given to me

[AciDCooL]

Re: Asus VH242H: 2 seconds to black..

Sorry to dig up an old thread I been reading allot of topics on this mather and finally made an effort to fixing it.
After replacing all the caps I still had the same 2 seconds to black issue with this monitor.
Since I'm not a electronics guru and can't desolder every part and check it. I took the inverter transformer and desoldered one. Since the coil screaming stopped with running only 1 transformer I hoped the 2 seconds to black would be gone to but it did not... So I went for the next best thing, since I know that all the caps are good now and higher rated then before I made a work around with the IC. I just shorted the R506 with r507 on the IC board. Now all the cfls light up and no coil whining. I know this is a workaround, but all the cool gadgets that you can test caps with and transformers are not in my shed nor near my budget for 1 monitor. I added a picture for future use if someone else has this monitor.

[chaser]

Re: Asus VH242H: 2 seconds to black..

Hi,

Apologies also for digging up an old thread, but I thought I'd also post my experiences.

I also have an Asus VH242H that started exhibiting the '2 seconds to black' behaviour. This wasn't a phenomenon I was familiar with until I started searching for possible causes and found this post.

Once I managed to pop open the case (after removing the three screws that hold the stand in position) I was able to get access to the power board. A quick look at the capacitors, and on first inspection there was nothing particularly obviously wrong. However, on closer inspection something didn't look quite right with C917 & C918. The tops looked to be bulging ever so marginally. These capacitors are in an area of the PCB that has clearly been running a bit hotter than the rest of the board.

I had a quick rummage through my spares box, but unfortunately I couldn't find any of the correct specification, so I decided to remove the capacitors from the board and test the monitor without them. To my surprise, the monitor jumped straight back into life!

I've ordered up a batch of Panasonic capacitors and will replace all the main capacitors on the board as a precaution.

As an aside, I noticed that the power LED is also not working. This is a bi coloured blue / amber LED, and I have verified that the blue part is broken. The amber part works fine. Unfortunately, I can't find a direct replacement, so will probably end up going for a blue / red LED instead - unless anyone can point me to a suitable supplier (in the UK, preferably)?

Here's a couple of photos of the board, one with the two capacitors removed...

Edit: Oh, and don't let the braiding from the cable that connects between the button / LED PCB and the main PCB touch the any of the heat sinks on the power board, otherwise you will get lots of sparks, and trip your ELCB! Fortunately no real damage done.

[pbz-313]

Re: Asus VH242H: 2 seconds to black..

Sorry to dig this one up, but I need help with my monitor;

I recently got the "2 seconds to black" syndrome, and tested all the caps using a multimeter (not an electronics expert here, but I do my best), and found one that was slowly reading it's way up to "forever". I replaced it with a capacitor of the same rating (1000uf, 25v), but it's still doing the same thing as before. I tried shining a light on the monitor after it went off, but couldn't manage to see an image (I do get an image when it first comes on, before it goes to black).

I really hope you folks can help em here; i tried sourcing a new power board, but they seem to be scarcer than hen's teeth and pretty expensive! Also, let me know if you need pics!

Thanks,

-pbz-313

[pbz-313]

Re: Asus VH242H: 2 seconds to black..

Never mind; just going to throw the monitor away. Why do I even bother with computers; may as well just go back to a string and two cups.

Thanks anyways, sorry to bother everyone.