It’s amazing how busy I’ve been lately, to the point that things are just piling up without a chance to get posted. Luckily, it’s now Easter break and I have a little time I can spend catching up. On Thursday, I dropped by the university to meet with my supervisor and spotted a fairly nice Samsung 27″ UHD monitor being thrown out. It was known to have intermittent picture and was out of warranty. As the uni was done with the monitor, I was permitted to take it home and attempt my own repairs. That evening, I carried the bare unit home under my arm on public transport, as if someone with a very oversized handbag. I might have looked crazy, but that’s just how far I’m willing to go to try and rescue some technology, especially as I don’t even have any monitors of that calibre.
The Unit and its Symptoms
Being pretty bulky, I had to throw it on my bed to snap some photos of it (from a rather unflattering angle). For the most part, it looks like most monitors, with a few little premium touches such as the wide silver brushed-look base and button-less front bezel.
Even though it’s a Samsung, the premium touches are pretty limited. For one, the stand had very limited adjustment, and the rear brushed appearance was merely a finish on the plastic. I’m sure it was expensive when purchased – it still retails for around AU$500 although the model is on discontinued run-out status.
In keeping with its slimmer profile, the monitor doesn’t feature an internal power supply. Instead, it relies on an external power adapter with a unique plug and unique 14V at 4A specification to power the monitor. Luckily I managed to take this home too, otherwise I wouldn’t have been able to test it at all.
The unit has a full model code of LU28D590DS/XY and was Made in China in June 2014. This is probably a very early unit as the version number is CY01.
The panel itself survived the train and bus ride home with only a very minor scuff. When powered up without any input, the monitor nicely displays its OSD diagnostics with no difficulty.
With an input applied, it started playing funny. First it would blink the input as if to say it was detected, and then not detected. When it did finally synchronize on the signal, the picture would be stable for a few minutes … and then …
… the image would tear, roll about, flicker and jump around constantly until power cycled.
The actual outcome did somewhat rely on what was being shown. Some static screens could be displayed with some ‘dimmed’ portions which were rapidly flickering. At one stage, I managed to get it to run 30 minutes with no problem. Trying to find the cause of the issue, I tried pinching around the screen edges with no change, as a result, I felt the TCON board was unlikely to be the cause. The tearing and jumping seemed to suggest a problem with some LVDS signal, maybe the loss of a clock or intermittent connection. I was hoping to find something that could be solved by a simple re-seat.
The smoking gun was when I bumped the HDMI cable accidentally, and the monitor went completely haywire. This suggested something mechanically related to the scaler board was the culprit.
The Repair Attempts
In order to attempt a repair, I had to get into the unit. This unit has just one screw – the one in the middle of the rear jack panel. Once this is removed, it’s best to start prying at a top corner with a screwdriver and run a spudger (I used an old plastic card) along the seam popping off the clips internally. The two halves separate to reveal the relatively sparse interior.
A big surprise to me was that the panel came from Innolux. The new name for Chi Mei Industries after a merger, it felt a bit disappointing. It’s like buying a Ferrari to find the internals were made by Hyundai. To their credit, CMI have been improving quite significantly, but I did expect to find a Samsung panel inside.
The layout is quite simple – scaler board in the middle in a metal “shell” which is left loose. Wire on the left is to run the panel backlight, wire on the right is for the joystick power and menu control. Wire at the top is the LVDS link that leads to the TCON board underneath the metal shield which is screwed in. This board would be part of the panel itself, and it seems to drive the panel as two halves. Maybe that was just the easier way to make a monitor with a large resolution.
Attempt #1 – Reseat
Nonetheless, my first attempt was just to unplug everything and plug it back in again. The cables on the left and right can be released by pushing on the latches and extracting the plug. The LVDS link at the scaler board can be unplugged by lifting the latch and lifting the FFC cable out, as it has some locating tangs on the cable. The other end of the FFC can be dismounted from the TCON board by squeezing the side latches inward and pulling the whole metal assembly outward.
Unfortunately, no dice. Doing this didn’t remedy anything, and the monitor was just as bad as it was before.
Attempt #2 – Scaler board SoC reflow
Given that a reseat didn’t do the trick, the next logical place to look is the scaler board. Removing the board already seems to suggest this board gets hot. A large thermal pad is adhered to the rear of the PCB to transfer heat into the metal shield of the panel as a heatsink. However, more concerning is that to the centre of the PCB, it has a slight yellowing suggesting heat stress. I could already guess the cause – even the Xbox 360 with its red ring of death fell victim to this – it seems it’s probably heating and cracking of BGA connections that was the cause.
Extracting the scaler board confirms that the main SoC resided exactly where the brown mark was. Everything else seemed in its place and the input jacks were all sturdy with no signs of damage. After all, the monitor behaved identically regardless of which jack I used.
This time, I decided to get out the heat gun and give the SoC a nice blast of hot air. This would hopefully reflow the solder and remake any bad joints. I gave it enough until I heard some popping sounds which normally indicates solder melting, but the unit was built on a fairly thin PCB, so some warping began to occur. As I don’t have a heat-plate to support the rear, I quickly lifted the board and heated it from behind to try and even out the stress. I was certain to have melted the solder, and left the board to naturally cool down slowly.
The first time actually made things worse. The unit didn’t start up at all despite a red LED on the board glowing. I took it out again and gave it another heat gun blast. This time, the board was revived, but for all of two minutes until a new left-right flickering intermittent mode started to appear. I decided to confirm the cause by tapping on the SoC position on the metal cage, which changed the pattern of intermittency before crashing the SoC and causing it to lock up. Removal of power and reapplication resulted in a monitor that didn’t start up at all.
Attempt #3 – BGA repair (?)
By this time, I normally call it quits. It’s beyond your average home-repair and anything with BGA in it is almost a guaranteed loss. But given that I can’t make things any worse than dead, I decided to just check that I was melting all the solder underneath the BGA by using the hot air gun to dismount it entirely. I was hoping there’d be relatively few connections, so I could just wick up everything, smear on a decent amount of leaded solder and reflow that for a good connection.
Alas, I was wrong. This thing was a crazy number of connections, along with many vias. I had flooded half of the pads with fresh leaded solder with flux as part of my cleaning strategy when I realized, I could never get this done.
This was especially true as the number of connections was absolutely staggering. I had no supply of solder balls to reball the chip, nor did I (or anyone I know) have the stencils to align the balls (or paste) onto the chip. Even then, it may well be a victim of its own heat soon after – the thin warp-prone PCB didn’t help matters one bit.
Alas, I decided to just throw in the towel and give in on the repair. It wasn’t going to happen and this 4K monitor would be inevitably in the scrap heap after all.
The Samsung monitor looked nice from the outside, but is a pretty basic affair. Inside, it was very much an Innolux panel (of Chi Mei heritage) married with some Samsung electronics and casing. Unfortunately, it seems, the Samsung part of it failed due to heat-related BGA connection cracking, and that rendered the unit intermittent. Attempts to repair it were fruitless.
Because the scaler board is now thoroughly hosed, the only option is to replace the scaler board. Unfortunately, spare parts are rare and sellers charge extortionate prices – the only one I found retailed for close to AU$200. At that price, it was not economical to repair the unit, especially considering the design flaw and the Innolux panel used. A new monitor would only be twice as expensive but would have a full warranty as well. As a result, the casing, panel and TCON board are all out for council clean-up.
In fact, it seems Samsung might be aware of the issue, as I spotted the images for the replacement scaler board having an additional thermal pad underneath the SoC, precisely where the brown mark is. This unit is probably a victim of being an early unit. It’s a shame where even such improvements are made, there is never any admission that older units may well have a design flaw that could limit its lifetime. I suppose as long as it makes the warranty period, the manufacturer couldn’t care less.