According to my NewEgg order history I bought that monitor 11 years ago in 2007. It doesn't even go up to 1080p. Over the years it ended up front-ending secondary and tertiary computers that I barely used. When it finally quit altogether, I stashed it in a corner and it stayed there for at least a year gathering dust.
It's customary when an old monitor goes out to use that event as an excuse to buy a new one with better features and chuck the old one in the bin. Given that and the age of this thing I think the odds against someone stumbling across this post and finding it useful are astronomical. But I've never been a fan of wastefulness, and if a perfectly serviceable bench monitor can be had for a couple of dollars worth of capacitors, they why not give it a shot?
Taking the thing apart was a bit of a chore. There are three screws in back along the bottom - the middle one hidden in the center of a foil sticker. However the back is actually held on by about two dozen tension clips that have to be carefully pried apart (I used one of those Lego pry-tools as a spudger to do it).
Once I got it apart, the problem was immediately obvious - four 1000uF 25v capacitors in the center of the power board were clearly swollen. (The capacitors in the yellow box in the image below are the replacements.) The bottom side of the board was coated in yellow-brown syrupy electrolytic fluid that had leaked from the dead capacitors. I happened to have a handful of capacitors with the right specs, so I cleaned the board, swapped out the bad capacitors and put everything back together. (The capacitors were attached to the board and the linear power regulators with gray epoxy - I'm not an electrical engineer, but I think doing that would transfer more heat from the regulators into the capacitors and cause them to fail prematurely - planned obsolecence?)
When I plugged the monitor in, I saw the familiar "Searching for Signal" box pop up for a few seconds, then, since I didn't have anything plugged in, it was followed by the "Power Saving..." box. Up to that point I thought "Yay, it works again!". Then instead of going dark and powering down, the screen went completely white - lit up as brightly as it would go. If I hit the "source" button, the screen would go mostly black, display the "Searching for Signal", then "Power Saving..." then back to a completely white screen.
Once I got it apart, the problem was immediately obvious - four 1000uF 25v capacitors in the center of the power board were clearly swollen. (The capacitors in the yellow box in the image below are the replacements.) The bottom side of the board was coated in yellow-brown syrupy electrolytic fluid that had leaked from the dead capacitors. I happened to have a handful of capacitors with the right specs, so I cleaned the board, swapped out the bad capacitors and put everything back together. (The capacitors were attached to the board and the linear power regulators with gray epoxy - I'm not an electrical engineer, but I think doing that would transfer more heat from the regulators into the capacitors and cause them to fail prematurely - planned obsolecence?)
When I plugged the monitor in, I saw the familiar "Searching for Signal" box pop up for a few seconds, then, since I didn't have anything plugged in, it was followed by the "Power Saving..." box. Up to that point I thought "Yay, it works again!". Then instead of going dark and powering down, the screen went completely white - lit up as brightly as it would go. If I hit the "source" button, the screen would go mostly black, display the "Searching for Signal", then "Power Saving..." then back to a completely white screen.
With a video source plugged in, the monitor worked perfectly normally - it displayed a nice clear bright picture with no problems, but the minute I tried to power it off, or the PC went to sleep, or the DVI cable was unplugged - bright white screen.
My first clue as to what was wrong was that when the screen went white, it didn't just "snap to" white. The whiteness would spread across the screen like a ripple - as though the blackness was "draining" out of it along the edges. Since the LCD works by darkening the screen in front of a florescent backlight, it made sense that what I was seeing was the LCD turn transparent as the power drained from it - the LCD was properly shutting down, but the backlight was staying constantly lit.
I took the monitor back apart to re-check everything - make sure I hadn't dropped some solder somewhere, or created a bridge somewhere. I de-soldered and checked a couple of other capacitors but everything checked out fine. Then I decided to completely strip the thing back down to give it a thorough cleaning and that's when I found what I had done wrong.
My first clue as to what was wrong was that when the screen went white, it didn't just "snap to" white. The whiteness would spread across the screen like a ripple - as though the blackness was "draining" out of it along the edges. Since the LCD works by darkening the screen in front of a florescent backlight, it made sense that what I was seeing was the LCD turn transparent as the power drained from it - the LCD was properly shutting down, but the backlight was staying constantly lit.
I took the monitor back apart to re-check everything - make sure I hadn't dropped some solder somewhere, or created a bridge somewhere. I de-soldered and checked a couple of other capacitors but everything checked out fine. Then I decided to completely strip the thing back down to give it a thorough cleaning and that's when I found what I had done wrong.
The power board has a 5-conductor wire harness connecting it to the backlight ballast board. This is the red box in the image below. On the backlight board, this 5-conductor harness connects a 5-conductor plug to a 5-conductor socket. What I did not notice is that on the power board side, the 5-conductor harness connects a 5-conductor plug to a 6-conductor socket. When I had first plugged it back in after replacing the capacitors, I simply lined the plug up with the bottom of the socket and pressed in. From that angle, it appeared to fully populate the socket, though in fact the top pin was unconnected. When I noticed this, I switched the position of that plug so that the bottom pin was unconnected, and viola! the monitor works like it should - shutting off the backlight when appropriate. Thankfully the plug and socket were designed in such a way that connecting it wrong didn't burn anything out.
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| In Red: the correct orientation of the backlight plug, with the plug aligned to the top of the socket so that the bottom pin is unconnected. In Yellow: the location of the four capacitors which had gone bad. |
Of all the lazy engineering, this one really took the cake. It's not the first time I've seen a wire harness with fewer conductors than the socket, but normally the plug will still match the socket to prevent exactly this sort of thing - the unused pin just won't be connected to anything.
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