Samsung C49HG90DMU 49″ 32:9 Ultrawide Gaming Monitor Stripy Screen Repair

A couple of months ago, I got given a Samsung C49HG90DMU 32:9 (3840x1080p) ultrawide 120Hz gaming monitor for spares/repairs because it only works OK once it has warmed up for about half an hour, until then it just displays a stripy white/purple screen which eventually changes bit by bit into a correct image.

Apparently issues with these ultrawide displays are fairly common, but I couldn’t find a definitive fix for this specific one. I tried multiple video inputs and it was the same across all of them – also, the overlay OSD has the same graphical issues, so the problem was likely not on the video input side but actually with the panel itself or its driver board.

I opened up the display to take a look inside and see if anything was obviously wrong – it was pretty tricky to work on because it took up most of my workbench. It’s important to try and support the weight of the panel when it’s upside-down too.

Once the stand has been removed, the rear cover is fairly easy to remove by carefully running a soft pry tool around its perimeter to pop out all of the clips that hold it in place.

Generally speaking, stripes means a digital issue, and the panel itself is probably OK because it works fine once the display warms up – but it could still indicate a faulty power supply if the voltages to the digital parts are noisy or insufficient. As such I pulled the power supply first to give the PSU board a visual inspection, taking care to avoid an electric shock from the large capacitors on the “hot” side – the PSU is held in place with two output cables and a couple of screws. I took the board out and I couldn’t see any obvious issues (burning, bulging capacitors, etc.), so I reinstalled and tested it, and its output voltages to the digital electronics and panel were both stable and seemed correct.

The next step was to inspect the digital electronics, which comprise a mainboard and what looks like a daughterboard for driving the display interface – again the mainboard is held in place with some delicate ribbon cables and a couple of screws.

Everything on the mainboard looked OK – I checked it over for bad solder joints on all of its connectors including the HDMI inputs, and the only aluminium electrolytic capacitor (a common failure point in consumer electronics) was a single surface-mount part which didn’t show any signs of physical leakage.

With the mainboard removed, I did notice that the ribbon cable between the mainboard and daughterboard didn’t seem to be fully inserted – I don’t think this display had been opened before (usually you can tell from marks in the plastic and a “crack” from the thread-lock on screws) so it’s possible that this was a factory issue or it had worked itself loose. It’s a bit tricky to tell from the picture below, but you can see that the cable is properly locked in place on the right-hand side but is slightly undone on the left-hand side. I pushed it into place on the left-hand side and it noticeably “clicked” and locked into place.

This led me not to trust the other cable connections in the display, so I removed all cable connections that I could see, cleaned them out with contact cleaner, then carefully reinstalled the cables to ensure that they were properly seated.

I also decided to replace the one aluminium electrolytic capacitor on the mainboard (a 100uF 25V SMD part), just because I had the monitor open anyway – I replaced it with a long-life polymer capacitor, which was a bit tricky because of just how much thermal mass this PCB has, it was really difficult to get the pads hot enough even with a pair of high-power soldering irons, so this part isn’t recommended.

I reassembled the display and tested it, and it started up fine immediately this time – in case it was still warmed up, I left it in my shed for a couple of days powered-off (which was pretty cold in the British winter), and it still worked fine even after that. Fingers crossed, it seems to have worked great in frequent use in my office for the past couple of months now.

This is my first ultra-wide monitor, I’ve been wanting once for a while now but couldn’t justify spending so much money on one, so I’m very excited to have been able to fix this one – I’ve replaced a pair of full-HD 21″ monitors with this one and it’s made a huge difference for gaming, I’m really loving it. It’s particularly good for War Thunder realistic battles because you can see around corners! It makes me wonder how much waste is created by things being thrown away when they could be such easy fixes.

The desktop calculator on my desk is a 1970s Monroe 610, which features a set of twelve miniature nixie tubes, and is one of my favourite collection pieces.