Task: Purchase a Multimeter for Troubleshooting Problematic Atari 8-Bit Computers
Needed: A multimeter
Time: 15-30 minutes
Introduction
The Atari 8-bit line of computers were well-made and remarkably resilient even after more than 40 years. I have had several dozen 8-bits pass through my hands over the years and have only encountered a few that didn’t work. I recently decided to level-up my repair skills and have successfully fixed several computers including an 800XL and a Commodore 64. I plan to do a series of posts on techniques, hardware, and tips for repairing 8-bit machines so that others can acquire this skill that is likely to be more important as these computers are soon to exceed 50 years old.
An essential item for testing the voltage paths and electronic components (e.g. resistors, capacitors, etc.) is the multimeter. This is important because it is possible for individual failed components to bring a system down even though the specialized integrated circuits such as the 6502 processor and the ANTIC graphics chip work fine. The opposite is of true as well.
I learned a lot about troubleshooting from Adrian Black of Adrian’s Digital Basement and Jonthan Halliday or FlashJazzCat. I highly recommend watching their videos and have previously posted about the FlashJazzCat YouTube channel. I also learned a lot from the AtariAge forums.
Instructions
Step one is to purchase a multimeter. There are many good ones to choose from on Amazon. I purchased a Chinese made Kaiweets HT118A from Amazon about five years ago for around $50. This is currently an Amazon’ Choice with over 22,000 reviews and ratings that are mostly positive. I have been happy with mine and think it works great. There are plenty to choose from. Here is a nice video review of the Kaiweets multimeter I have that includes a good demo of how to use it.
Step two is to read the instructions if you have never used one before. Also find some instructional videos online. Note all the safety instructions, cautions, and warnings that can cause personal harm or damage to your computer or multimeter.
Step three, use your new multimeter to test the voltage on your Atari circuit board. You will see in the photo below that I have the black lead attached to an alligator clip connected to the metal box of the RF modulator to serve as ground. I can then use the red probe to test the voltages on different components and chips. Make sure you are using a trusted power supply such as those you can buy newly made. A good first test is to make sure the 6502 Sally CPU is getting 5V on pin #8 (labeled Vcc in this schematic). You can also probe pin #1 (labeled Vss) that is the ground for the chip. This should read very close to 0V. Follow the pinout diagrams from this website to test Vcc and Vss on the other main chips such as ANTIC and GTIA.
Comments
Test as many chips and components as you can to get some practice.
Testing the voltage with a reliable power supply should be the first order of business when troubleshooting a nonworking 8-bit computer.
Be sure and read all the warning and cautions about using a multimeter that are supplied in the documentation of the unit you buy. For example, exceeding the maximum voltage of the unit can damage it.
Also be careful not to shock yourself! Touching a 5V power line can provide a shock. Capacitors are also notorious for releasing larger voltages.
Another tip is to avoid touching more than one contact at a time with the probe. This can create a short and damage your components.