Hello, I'm having an unusual issue with my 20th Anniversary Macintosh.
I've replaced electrolytic capacitors on over a dozen macs before with 100% success. However, this TAM seems to have the [Apple] key continually pressed down in MacOS. I even confirmed this behavior via the "Key Caps" program in OS9. I also plugged in a known working keyboard, and the same result presented.
I decided to try starting with only a mouse attached, and when I went back into "Key Caps", the [Apple] key was no longer pressed. So, there is some signal confusion going on between the ADB controller and the keyboard. Oddly though, the [Apple] key is the only key affected, and, of course, makes normal use of the computer impossible, since OS9 thinks I'm trying keyboard shortcuts instead of normal typing.
I pulled down an ADB whitepaper that discusses the technology behind ADB, to which I learned that it is an asynchronous pulse-width signal (hence why there is only a single signal wire). So, now knowing that ADB signals are pulse-width in nature, clearly when the ADB controller identifies a keyboard, it thinks the keyboard is sending a perpetual [Apple] keystroke.
*Whew* now, all that being said, my question is: could replacing an electrolytic capacitor with a tantalum equivalent somehow impact the clock speed, which the ADB controller relies on to interpret keystroke pulses? Also, does anyone have a technical paper, or equivalent that discusses the TAM's logic board in detail? Preferably, the paper would identify sections of the board where various functions are performed. In the attached image (which I created, inspired by Bruce of "recapamac.com.au"), the lower-right section is where the ADB and serial ports are located (ADB is the bottom-most port).
If the TAM's logic board is set up in...logical sections, then I would hypothesize that both or either the 47uf and 100uf caps are part of the ADB circuit.
Hopefully, someone has the answer, or knows a guy who knows a guy who has the answer, and can point me in the right direction
Here's the ADB white paper link
The photo in question. All focus is on the bottom-right corner.
Thank you!
I've replaced electrolytic capacitors on over a dozen macs before with 100% success. However, this TAM seems to have the [Apple] key continually pressed down in MacOS. I even confirmed this behavior via the "Key Caps" program in OS9. I also plugged in a known working keyboard, and the same result presented.
I decided to try starting with only a mouse attached, and when I went back into "Key Caps", the [Apple] key was no longer pressed. So, there is some signal confusion going on between the ADB controller and the keyboard. Oddly though, the [Apple] key is the only key affected, and, of course, makes normal use of the computer impossible, since OS9 thinks I'm trying keyboard shortcuts instead of normal typing.
I pulled down an ADB whitepaper that discusses the technology behind ADB, to which I learned that it is an asynchronous pulse-width signal (hence why there is only a single signal wire). So, now knowing that ADB signals are pulse-width in nature, clearly when the ADB controller identifies a keyboard, it thinks the keyboard is sending a perpetual [Apple] keystroke.
*Whew* now, all that being said, my question is: could replacing an electrolytic capacitor with a tantalum equivalent somehow impact the clock speed, which the ADB controller relies on to interpret keystroke pulses? Also, does anyone have a technical paper, or equivalent that discusses the TAM's logic board in detail? Preferably, the paper would identify sections of the board where various functions are performed. In the attached image (which I created, inspired by Bruce of "recapamac.com.au"), the lower-right section is where the ADB and serial ports are located (ADB is the bottom-most port).
If the TAM's logic board is set up in...logical sections, then I would hypothesize that both or either the 47uf and 100uf caps are part of the ADB circuit.
Hopefully, someone has the answer, or knows a guy who knows a guy who has the answer, and can point me in the right direction
Here's the ADB white paper link
The photo in question. All focus is on the bottom-right corner.
Thank you!