display - Philips 190V LCD Monitors - Turns off and then back on loop
2014-07
xZero
I got Philips 190V as a gift, which would be a nice replacement for my old AOC 9K+ which consumes a lot of power by my calculations.
I have a lot of experience with electronics, and LCD monitors, but this one is a mystery to solve.
The problem:
The monitor turns off after a few seconds, power LED also turns off, and then turn on again, works well a couple of seconds and goes off again, and as always the power LED together with him, and so a couple of times or infinitely...
Then sometimes happen that it will not work anymore until I press button ( any except Power ) and works as long as I hold the button, as soon as I let it extinguishes.
There are also other symptoms:
So for example, sometimes starts blinking together with power LED and then turns off and stays off until I turn it on again by pressing the power button. Then sometimes happen that it will not work anymore until I press button ( any except Power ) and works as long as I hold the button, as soon as I let it extinguishes.
Sometimes it just works, but suddenly menu opens...
Then sometimes, it works, but if I press any button, it will turn off and will stay off until I release the button.
Power button works very rarely.
I figured out that the problems gradually weaken when it is well warm .
Sometimes working at 2 -3h and suddenly problems start again.
Also, sometimes, when PC is off, it doesn't want to go sleep, it just shows "No video input"... But that's not important to fix.
I disassembled it, power board gives the OK voltages even when the problem is happening. For my visual inspection, it looks fine.
Video board also looks right. Neither the one nor the other, no inflated capacitors.
I checked the main filter electrolytic capacitor at high voltage section and the output filter electrolytes (2200uF x2) at the low voltage section, with my primitive method of measurement, without appropriate instrument and using just a multimeter - These capacitors seems like OK.
I checked and 2-3 Low Capacity (1uF or more) capacitors on the video board, and they all seem OK.
I measured the voltages on the voltage regulators, and they seem to be normal.
Disconnect the front panel buttons, if they are defected, but it does not solve the problem .
I ran out of ideas, my soldering iron is broken so I only get one with a thick tip, making it difficult to de-soldering a small capacitor on the video board.
Should I get one by one and test them? There is a lot of them... And with this soldering iron I'll have hard times....
Does anyone have any tips and ideas?
Thanks!
xZero
The problem cause is slightly banal, it was a front panel failure. When I disconnect it, monitor works, immediately after connecting, the problem appears.
I still don't know where on the simple front panel PCB problem is, but it contains several SMD parts - resistors and capacitors. They might be faulty. Other parts are push buttons, and 3-pin two-color LED diode.
Jader Dias
As long as I used my VGA cable, my LCD monitor worked fine. But when I switched to my DVI cable, sometimes my monitor turns off. When it happens the power light still on, the screen is dark but the very darkened images can be seen in certain angles in certain circumstances, so I supposed that just the backlight has turned off. I presume it's the cable or the connectors fault, but I am asking here if you had a similar experience, and if the only solution is to buy a new cable.
My monitor has both connections (VGA and DVI) but my video card has only DVI. So when I used the VGA cable I used with an adapter between it and the video card.
** UPDATE ** It wasn't the cable. I switched back to my old VGA cable and it is still with problems.
Sampo Sarrala
Looking for picture behind dark screen
If you can see picture even while backlights are not working then problem almost certainly lies in monitor powersupply/inverter board.
Sometimes it will be extremely hard to see picture when backlights are gone. You should try external lighting at different angles and at different luminosity. If possible, it could help if there is fullscreen animation running while checking this, for example cartoons with great contrast and bright colors.
Causes of darkness
Blown/leaking/dry capacitors are very common problem with flat screens, they are also pretty easy to check for defects (most of time visual inspection is all you need).
Capacitors are also relatively cheap and pretty easy to replace (if you know how to use soldering iron), just remember to check orientation for +/- leads (likely marked on board). However you should also inspect those high voltage cables for burn marks, especially near cold cathode tubes (not found from screens with LED backlights).
More on topic
- On laptops, there's small inverter board located just under screen frame casing (in most models) that is often cause of black screen. These could be very cheap for some models.
- See PSU failing or Mainboard failing? for picture of defective capacitors.
- There's also simple power cord test that you might want to carry out:
Pressing power button (pulling plug out for few seconds) many times also speaks toward broken PSU case as when you press and release button it will discharge capasitors and then immediately charge them again, doing this many times could still make almost broken capasitor to work once again for some moments.
Manuel Ferreria
Are you sure there is no setting in your OS that controls backlight? If Vista/7, try checking the powersaving feature to make sure nothing is dimming backlight.
EDIT: So, no use. If your PC came with a DVI/VGA adapter, try it on the faulty DVI port. That way, you can rule out DVI Connector (if it works well) or DVI cable (if it doesn't).
If everything else fails, try borrowing a cable from a friend, or get a really cheap one, that at least works. If it was the cable, you can later buy a higher quality one.
This way you rule can out the most expensive parts of the issue, the monitor or the video card.