My equipment:
Acer X223HQ 21.5” LCD Monitor connected through VGA cable to a Dell Optiplex 740 desktop computer dual-booting Window 10 and Ubuntu Linux.
Monitor is about four years old and worked trouble-free for more than three years.

The problem:
Computer boots from cold without difficulties, monitor starts up as normal and the boot process and desktop image appear clearly and distinctly on the monitor screen.
However, 40 seconds after initializing the boot, the blue monitor power light goes off, stays off for 3 seconds, then the orange power light comes on for one second followed by the blue light and a normally functioning monitor screen once again.
Note that the computer itself does not power off during this sequence.
However, this time, the blue power light on the monitor stays on for just 12 seconds and is followed, as before, by three seconds of no power, then one second of orange power light whereupon the blue power light and screen come on again.
In every successive “cycle” the blue power light and screen remain on for less and less time until finally, after about seven cycles, settling out at three seconds on followed by three seconds off, one second orange light and then blue power light and screen on again for three seconds.
And so on ad infinitum.
Or at least for one full hour which is as long as I’ve left it in that condition.

If, after shutting down the computer plus monitor, I start the system up again immediately, it continues where it left off.
That is, the monitor cycles on and off repeatedly with the blue power light and the screen staying on for just three seconds on each cycle.

However, if I leave the system shutdown for an hour or more and start up the system again, the monitor behaves just as I describe in the initial paragraph of this section. That is, the blue power light and screen stay on for 40 seconds, then off for 3 seconds, then 1 second orange light then blue again for 12 seconds and so on.

Here's a shot of the power supply board:

And here's the main board:

What have I done to try to examine the problem?:
1. I checked the computer, the power cable to the monitor and the VGA cable on another monitor and everything works perfectly. So these three items can be ruled out as contributors to the problem.
2. I opened up the monitor and took out the power supply board and the main board looking specifically for blown capacitors. However, none was found on either board.
3. Nevertheless, I replaced 12 of the 15 caps on the power board leaving just three untouched (1x10uF/50v, 1x225uF/25v and the large filter cap of 120 uF/450v).
4. I then put everything back together but the monitor behaved exactly as before. No change whatsoever was observed.
5. I throughly inspected both sides of the boards looking for either burnt components or bad solder joints. However, neither was found.

What do I think may be happening?
It all sounds, to my inexperienced ear, like something may be overheating and causing the monitor to power off for a few seconds during which time it cools down sufficiently to power on again.
Or perhaps, a capacitor is failing to discharge correctly leading to a shutdown during which the cap discharges allowing the monitor to start up once again.
But I’ve already replaced 12 of the 15 caps on the power board so, if it really is the power board that’s causing this problem, it suggests that perhaps the large filter cap (120uF/450v) is the culprit.
Or it’s something else that I just haven’t thought of?
That’s why I’m here.

What do I expect from this forum?
At present I’m lost and other than purchasing a new power supply board I really am unclear what I can do next.
So, I’m looking for comments, tips, pointers, hints or basically anything that might help me resolve, or at least understand, this conundrum.
Thanks in advance.

 

Hello,

How is the condition of the 120 μF / 450 Volts capacitor?
How does the top of it look like?
Is it bulged?
If so it has gone bad and will give strange effects when it gets warmer inside the monitor.

Bertus

 

Hello,

How is the condition of the 120 μF / 450 Volts capacitor?
How does the top of it look like?
Is it bulged?
If so it has gone bad and will give strange effects when it gets warmer inside the monitor.

Bertus

Hi Bertus
Thanks for the reply.
No the 120μF/450v cap is not at all bulged. Indeed, none of the capacitors on either board were or are now bulged or show any signs of distress.
Nevertheless, I may well change out this cap basically because I'm running out of options although I know it's a long shot.

 

It certainly sounds as though this is a heat-induced problem.
If all the caps are ok, I'd consider re-soldering the joints of any component which gets hot in use, and checking that semiconductor devices have good thermal contact with their heatsinks.

 

It certainly sounds as though this is a heat-induced problem.
If all the caps are ok, I'd consider re-soldering the joints of any component which gets hot in use, and checking that semiconductor devices have good thermal contact with their heatsinks.

Hi Alec_t
Thanks for your thoughts.
The power board has three heatsinks and the components (2xFETs on one, 1xFET on another and an Audio IC on the third) on all appear to be well secured (screwed) to the heatsinks with no gaps between the component and the metal.
The main board has no heatsinks.
Additionally, there is no dust whatsoever on any of the power board's heatsinks, nor on the perforations in the metal cage where the PCBs sit. Further, there is no dust or obstructions impeding air getting through the air slots in the outer plastic casing.
Also, considering that the monitor shuts off for a mere three seconds in every single case whether started up from cold or after running for an hour or so, it seems to me unlikely that, if it were an overheating problem, that a mere three seconds shutdown would be sufficient to cool the overheated component down so that it starts up again.
Yes, resoldering some of the joints may be worthwhile, although as I mentioned in my first post, I didn't see any obvious dry joints in a fairly thorough inspection.
But it's certainly worth another look.

 

Have you checked all of your voltages to see if they are nominal?

This might not be the supply at all rather the power saving circuit that shuts down the monitor when there is no signal.

 

Hi spinnaker
Thank you for your suggestion.
No, I haven't measured any voltages on the boards.
This is the first time that I've opened up an LCD monitor and I haven't yet powered up the board in its disassembled state.
However, I've posted my issue to other forums over the past few weeks assuming that mine was a known problem with a relatively simple solution.
Given that, in total through the various forums, my issue has had more than 200 views without any easy solution emerging encourages me to believe that this is not going to be an easy or straightforward fix.
My present thinking is that it may be best to just purchase a replacement powerboard which I can get from a large country in the east for about US$40 including shipping.
Indeed, I can't even be sure right now that this is a power supply board problem. But if not, it's almost certainly going to be the main board that's at fault. I can get this latter from the same source for less than US$30.