I have a Macintosh Plus that I bought and restored a year ago, and it has worked beautifully since then. At the time, I fully recapped both the analog and digital boards.
Unfortunately, last week, I accidentally plugged in what turned out to be a defective cable into the SCSI port. This seems to have caused a short circuit—the cable became hot, and the screen went black. I quickly turned the unit off, but the damage was already done.
I suspect the power supply took a hit because, ever since, it has been making a clicking sound at approximately 4.2 Hz. A visual inspection didn’t reveal any damaged components. With no logic board connected, I checked the +12V, +5V, and -12V lines using an oscilloscope and observed the voltage trying to establish itself before cutting off and restarting in a loop. Checking the power lines' load resistance didn’t indicate any obvious short circuit either—though I couldn’t find the expected load values.
Has anyone experienced a similar issue? Any advice on which components I should inspect first?
Thanks, everyone!
Unfortunately, last week, I accidentally plugged in what turned out to be a defective cable into the SCSI port. This seems to have caused a short circuit—the cable became hot, and the screen went black. I quickly turned the unit off, but the damage was already done.
I suspect the power supply took a hit because, ever since, it has been making a clicking sound at approximately 4.2 Hz. A visual inspection didn’t reveal any damaged components. With no logic board connected, I checked the +12V, +5V, and -12V lines using an oscilloscope and observed the voltage trying to establish itself before cutting off and restarting in a loop. Checking the power lines' load resistance didn’t indicate any obvious short circuit either—though I couldn’t find the expected load values.
Has anyone experienced a similar issue? Any advice on which components I should inspect first?
Thanks, everyone!
