[Ham-Mac] Mac Classic II Serial Port Kaput

[Chris Smolinski]

>Anyone have any ideas or experience with faulty serial ports on the older
>machines?

Yep! I've fried ports on the following machines: SE/30, Quadra 700, 
PowerCenterPro. If you're up to soldering parts, you can often fix it 
yourself. Usually it is the driver or receiver chip that fails, 
typically an AMD 26LS30 and 26LS32. Probably SMD on newer Macs, may 
be DIP on solder Macs. If so, install a socket! Some Macs have 
filters on the serial ports as well that can fail.

My personal opinion is the ESD protection on Mac serial ports is 
lousy to non-existent. The only time I have fried a serial port on a 
PC, I accidently applied 1KV from a supply capable of sourcing 5 mA 
to the data receive line (don't ask!). And it only fried that one 
port.

I like the fact that the ports on a Mac are differential, but they 
should have been made +/-12V to better interface with RS232, not +/-5 
Volts. But too late to complain about a decision made 20 years ago ;-)

I installed a 4 port serial card on the PowerCenterPro, so I can add 
lots of serial devices. I have a few radiation detectors on it now 
(see http://www.blackcatsystems.com/GM/page6.html and 
http://www.blackcatsystems.com/GM/compare.html for online graphs)