Merit Megatouch 5 Issues

Offered to help out a friend whose husband had an upright Megatouch 5 (CRT-260 motherboard) that had some issues:

  1. Would randomly crash when touching the touchscreen
  2. Would randomly hang or crash even when left alone
  3. After left running for a little while (like, 15 minutes) calibration would “drift,” causing touches to track incorrectly

After opening it up, the touchscreen was covered in dust and the neoprene strips on the edges of it were pretty torn up and had a bunch of debris on them.  Cleaning the screen, strips, and then reapplying the strips with some thin double-sided tape cleared up the touch-the-screen-and-it-dies problem.

Saw a bit of ripple on the power lines that got worse as it warmed up.  Doing a cap job on the power supply (which had a LOT of leaky and/or swollen caps) cleared up the power and the random crashes.

The touchscreen tracking problem was interesting.  When it starts to go out, tracing vertically down the screen causes tracking to move diagonally!  I had never seen anything like it before.  (You can see a video of what it looks like.)  Definitely not a serial data problem – tracking is not random, and the movement is linear.

I thought the power supply fixes would nail it, but no.  The touchscreen issue turned out to be thermal-related.  Inside of the controller is this chip (circled):

Bad Touchscreen Controller

The chip did not get hot to the touch – it barely got warm at all.  But it was the bad one.  Hitting it with the component cooler spray caused the tracking to function correctly for a little while.  Custom chip, so no replacements on hand.  

As luck would have it, an eBay user was auctioning 4(!) of them off, and I was able to get a good deal on them.  Touchscreen controller board replaced and recalibrated and all is well once more.

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