First off I'm a firm believer that everyone should have a logic probe in their toolkit since there so much you can do with it and while it's helped me tremendously over the years, when it comes to data signals or anything timing specific it has some limitations, this is when it's time to break out the oscilloscope.

Seeing as I finally purchased a new oscilloscope for my test bench, and it arrived on Friday, I figured I would test it out by looking at switch matrix signals; while there is tons of good information out there on how to troubleshoot the switch matrix, I figured why not toss out the visuals of how it works here on pinside as I know many of you will find it interesting and hopefully clarify some of the theory on how the matrix works.

The theory itself is pretty simple, any inactive row or column is going to be at a logic high; when its time for the computer to scan the switch matrix for closed switches, it enables each column one at a time by driving it low, while monitoring all eight rows; any closed switch in the active column will drive the entire row low for the duration of time that the column is active. In the following picture, you can see the column1 drive signal measured on J207-1. This signal is of a very short duration, about 30us and happens roughly 488 times a second...

Switch_Matrix_PRF_(resized).png

each column in the matrix is sequentially checked until all columns have been checked for closed switches. For some reason the frequency counter was showing less that 15HZ, not really sure why, I'll need to look into that.

WPC_Switch_Columns_(resized).png

For the test setup I used a WPC89 MPU, Pinitech.com matrix tester with the following switches turned on:
Row 1 switches in columns 1,2,3, and 4
Row 2 switches in columns 2 and 4
Row 3 switches in columns 1, 3, and 5

For those unfamiliar with the switch matrix tester, each of the eight red DIP switch banks is a separate column, and each switch in the bank is for a row in that column, this allows you to lock individual switches into specific states for testing.

Test_setup_(resized).jpg IMG_1746_(resized).JPG

The following images illustrates how row 1 was pulled low for the entire duration that columns 1 -4 were enabled since it contained an active switch in all four columns; rows 2 and 3 alternated states as only every other column in those two rows contained closed switches.

WPC_Switch_Rows_(resized).png

Hope you find this information useful in diagnosing those pesky matrix issues, and be sure to check out the information on pinwiki http://pinwiki.com/wiki/index.php?title=Williams_WPC#Switch_Matrix_Problems

Terry, thanks for posting and adding the pinball rehab link, it's an outstanding resource!

I don't mind at all, please help yourself to any of the images you want to use.

I was skeptical of the Rigol, but did my homework on it and I'm glad I decided to buy it, I picked up the 1054Z off amazon for $399 https://www.amazon.com/Rigol-DS1054Z-Digital-Oscilloscopes-Bandwidth/dp/B012938E76/ref=sr_1_1 I hate to sound like the guy in the youtube review but $400 for a 4 channel oscope that comes with 4 probes ... whats not to like? The two primary complaints people seemed to have with it was the small font size and the fan noise; I really don't see whats to complain about though, the font it very clear and I cant even hear the fan unless the room is completely quiet. The layout seems easy to navigate and there is on screen help for everything.

There are some minor things I wish it had...a 50% trigger level button or auto 50% trigger feature, an "all waveforms off" button would be nice on a 4 channel scope, and auto probe sensing probes would be another nice feature, but this would drive the price of the unit and probes up, and realistically I cant even remember the last time I used a 1X probe.

In the end though, $400 for a 4-channel scope!

In the previous pictures you can see that the frequency counter is reading less than 15HZ, I found that this was an unexpected result of turning on HFR for the trigger channel, I enabled this to provide a crisper image but didn't notice the impact it had to the frequency counter.

I also have an image of how a shorted diode effects the matrix, feel free to use this if you wish.

Bad_Diode_(resized).png