In vintage computing the main benefit of solving a problem is it helps you to find the next problem.
After fixing my IIsi logic board (caps) and its PSU (caps) I found the ADB keyboard beginning to act strangely. Sometimes it seemed dead, other times it would pass through a couple of characters then freeze.
Mouse was fine, so I reckoned the ADB controller on the logic board must be OK, and the cable was most likely OK.
Soft power button (reset) also worked reliably. In fact, pressing the power button after a number of failed keystrokes resulted in display of the first 2-3 characters (apparently released from the keyboard's onboard buffer) and then sometimes a string of random characters that would continue until hitting the power button again. Clearly the controller chip was getting garbled signals somehow, or was corrupted.
Opened it up, blew out a bit of accumulated wool, inspected PCB carefully. No cracked traces or dry solder joints anywhere. However, there are two electrolytic caps, one at each end of the controller chip - both 1uf x 50v.
Replaced those two caps and problem seems solved. They must have been failing and letting some sort of electrical noise disturb the controller logic.
The keyboard is M00487, originally sold with a Mac Classic.
Rick
After fixing my IIsi logic board (caps) and its PSU (caps) I found the ADB keyboard beginning to act strangely. Sometimes it seemed dead, other times it would pass through a couple of characters then freeze.
Mouse was fine, so I reckoned the ADB controller on the logic board must be OK, and the cable was most likely OK.
Soft power button (reset) also worked reliably. In fact, pressing the power button after a number of failed keystrokes resulted in display of the first 2-3 characters (apparently released from the keyboard's onboard buffer) and then sometimes a string of random characters that would continue until hitting the power button again. Clearly the controller chip was getting garbled signals somehow, or was corrupted.
Opened it up, blew out a bit of accumulated wool, inspected PCB carefully. No cracked traces or dry solder joints anywhere. However, there are two electrolytic caps, one at each end of the controller chip - both 1uf x 50v.
Replaced those two caps and problem seems solved. They must have been failing and letting some sort of electrical noise disturb the controller logic.
The keyboard is M00487, originally sold with a Mac Classic.
Rick
