Task: Replace Faulty Capacitors on Your Atari 8-Bit Computer Circuit Board
Needed: New capacitors, desoldering iron, hot air rework station, soldering iron and solder
Time: 30-60 minutes
Introduction
Electrolytic capacitors are notoriously unreliable on retrocomputers. The capacitors used in 1970s and early 1980s on the Atari 8-computers don’t seem to fail too often. However, they do fail. I was repairing an Atari 800XL that needed a new GTIA chip and a new POKEY sound chip. Once replaced, the Atari still had soft sound and was missing some notes. I tracked down the problem to an electrolytic capacitor (C24) in the sound amplifier circuit. The capacitor, shown below, was discolored and clearly needed to be replaced. A new capacitor fixed the problem. Telltale signs of a capacitor gone bad are discoloration, bulging at the top or bottom, and leakage which can damage the circuit board. You can also test them with a multimeter to check whether the capacitance is consistent with the Farad rating is on the label. Fortunately, replacing bad caps is not that hard if you know basic soldering and desoldering.
Instructions
Step one is to discharge the capacitor. This is important to prevent getting shocked. You can use a multimeter to check the voltage of the capacitor as a measure of how much charge is left. Either wait for it to reach zero volts or manually discharge it as described in the article I linked to.
Step two is to test the Farad rating of a suspect capacitor with a multimeter as I have described before. The one I replaced was rated at 10 micro Farads.
Step three is to desolder the capacitor from the underside of the circuit board. I have previously posted about tips for purchasing and using a desoldering iron and a hot air rework station that helps get components off the board following desoldering without damaging the traces. Make note of the polarity and orientation of the capacitor to match with the new one. You can see the + sign next to the capacitor in the photo below.
Step four is to solder in the new capacitor in the same polarity orientation as the original. Make sure the Farad rating is the same and the voltage rating is at least as big. Console5 is a great source of capacitor kits for retrocomputers. Fortunately, these capacitors are relatively inexpensive.
Step five is to test the new capacitor by booting the Atari and checking for correction of the problem.
Comments
The ability to replace capacitors is an important skill to have because they do fail from time to time.