My sports car club has several numeric displays connected to our timing systems. One of them decided to fall over due to a strong wind gust, and quit working properly. This article explains the theory of the display and how I went about making it work again.

THEORY OF OPERATION

The display is an electro-mechanical device. It gets a time to display from the timing computer, and converts the time to what is known as a seven-segment code. Each numeral is made up of seven-segments to display the correct number.

  When all seven segments are "on", the number 8 is shown.

When the center segment is "off" the number 0 is displayed, and so on. The segments are rotated by means of a permanent magnet (right picture) and an electro-magnet (left picture), and ride on tiny plastic "bearings" that snap in to holders. More on them later in this article.

When the current is applied to the electro-magnet in the positive direction, the segment rotates to the "on" position, and when the current is reversed, it rotates "off".

THE FIX

When the wind knocked the display over, the impact knocked some of the segments out of their holders. In some cases, the bearings just popped out, in others, the bearings fell off completely. I was fortunate enough to find all of the loose bearings in the bottom of the display cabinet.

I had to remove each damaged numeral (4 screws and unplug), and painstakingly with tweezers place the bearing back on the axle and snap back in to place. As I said earlier, I was able to find all of the bearings. Took about 2 hours to complete and test. All is well.