from the old NLG site...
So i'm working on a Piggy Banking dotmation machine and there's no
lamp matrix. That is, the lights for the front panel buttons do not work.
The lamp matrix consists of several rows and columns, with the electronic
cross-section of a row/column signifying a particular lamp.
Usually this problem is a broken wire. That is, one row and one column
wire "daisy chains" from lamp to lamp. If the wire breaks, all lamps
"upstream" won't work.
But in this case, apparently there was a short in the lamp matrix. Gee
how could i tell? Below is a picture of the Back Plane board. I would
say there was a short alright! Notice that the back plane E-EPROM
survived this without fault, but a trace or two for the lamp matrix burned
right off the board!
I did repair this board and use it in a game. worked fine after the
repair. but it was probably a bad I/O board that caused this
problem on the original game. Too much current draw from a
shorted transistor in the lamp matrix, and the traces burnt up
on the backplane board. If one of the TIP107 transistors shorts,
18 volts goes to the lamp matrix (instead of 6 volts). This will
burn up the bulbs and the board traces in a hurry.
Williams uses 18 volts for the lamp matrix. but the CPU pulses
the voltage (like a switching power supply) through the I/O
board's TIP107 transistor to bring the voltage down to 6 volts.
If one of those TIP107's goes bad, the result is shown below.
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