Use a Multichannel Oscilloscope to Test Multiple Pins of an Integrated Circuit Simultaneously (15-30 mins)

Hardware, Troubleshooting

Task: Use a Multichannel Oscilloscope to Test Multiple Pins of an Integrated Circuit Simultaneously

Needed: Multichannel Oscilloscope with Multiple Probes

Time: 15-30 mins

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Introduction

I have previously posted about using an oscilloscope for testing and troubleshooting failed chips such as the 6502 CPU and ANTIC. However, this was done one signal at a time. Most modern oscilloscopes have at least two channels making it possible to monitor multiple signals simultaneously. My Siglent SDS 1104X-E has four channels and came with four probes. Below is a photo of the four probes (color coded yellow, red, blue, and green). Here, yellow is attached to the Phi 2 pin (the clock signal) while blue is attached to data 7, red to Sync, and green to address 11. Here I am monitoring multiple signals on a single chip. However, it might be useful to monitor a single data or address line across multiple chips, for example.

Using Four Oscilloscope Channels to Monitor Activity on an Atari 800XL 6502 CPU
Using Four Oscilloscope Channels to Monitor Activity on an Atari 800XL 6502 CPU

Instructions

First, attach two or more to the oscilloscope with color matching to make it clear which probe is attached to which pin. My probes came with little colored bands that can be attached to the probe and to the oscilloscope connector. I matched these up with the color printed on the oscilloscope and matched my ground clip colors as well (with back for blue).

Second, attach each probe to the pin you want to monitor. Note that I attached printed pinouts to each of my chips to make it easier to find specific pins.

Third, attach each ground clip to the ground plane or other ground source. I use holes in the ground plane that runs along the perimeter of the circuit board to attach my ground clips.

Fourth, power up the oscilloscope.

Fifth, power on the Atari.

Here is a short video from the four pins I monitored. Below is a still image of the same.

Four Channels Monitoring Four Pins of an Atari 800XL 6502 CPU
Four Channels Monitoring Four Pins of an Atari 800XL 6502 CPU

Comments

I found this to be a very informative exercise. Not only can you better understand how these old systems work but you can up your troubleshooting game by being able to monitor multiple pins or multiple chips simultaneously.