Hello Bob,

The line isolation circuit card that you designed wasn't the ALIT (5ESS
Circuit Packs TN138, TN139, and TN140 as I recall) was it? I just have to
ask since I was a very young Western Electric factory engineer way back when
the Bell System actually existed and manufactured their own stuff. I wrote
the factory functional circuit tests for that card! As I recall, it was one
of the first to use the (then brand new) Intel 16-bit 8086 microprocessor,
but still used a whole lot of mechanical relays to connect the Metallic
Service Unit to the customer line under test in the Line Unit.

Bob Shuman - Who is one of the few still working at the Network
Software Center/Indian Hill complex over a quarter of a century and three
company names/corporate logos later!



"hr(bob) " wrote in message
ps.com...
Arfa is right, be careful what you do to the phone company line. I
designed several central office test line circuits in my years at Bell
Labs. One circuit was used to detect false power crosses and grounds
on subscriber lines, and put fairly high voltages out onto the
subscriber lines when the central office was suspicious of a line
problem. Also the 90VAC ringing signal has a peak voltage of about 125
volts and can give you a very nasty surprise if you happen to be
touching the line when the phone is either ringing or perhaps being
tested because they sense something abnormal about the line.

H. R.(Bob) Hofmann