Re: Modem Problem

[Eric Jacobs <jabox@geocities.com>]

David Empson wrote:
> 
> I had a lightning strike near my house a few weeks ago, which destroyed
> my modem _and_ the modem port of the computer to which it was connected
> (my PowerMac).
> 
> Nothing else in the house was damaged, so my theory is that there was a
> power surge which mostly affected the modem because it was also
> connected to the telephone line.  The earth voltage would have risen
> sharply, but if the telephone line did not leap in sync with the power
> lines then there would have been a large voltage differential inside the
> modem, causing an arc over to the telephone line circuitry.
> 
> The modem's power supply was damaged, along with at least one chip (the
> 1488 RS-232 line driver which was connected to the Mac).  I haven't
> tested the modem beyond that, but my insurance company got it tested and
> agreed that it was damaged by a power surge.
> 
> The damage to the 1488 probably resulted in a reduced power surge going
> down to the Mac and damaging its line driver/receiver chips for the
> modem port.  The printer port is fine, and the rest of the computer has
> been working perfectly since then.

I have resurrected quite a few "broken" modems by replacing the RS-232
line drivers on the board. Most of them are at least pin-compatible with
the 1488, which is widely available and inexpensive. If you see the TD
and RD lights working on the modem, but the computer can't communicate,
there's a good chance it's a line driver problem. If the drivers are
fried in your computer, you have a bigger problem. It's one thing to do
a last-ditch effort to recover a non-working modem, but I wouldn't try
it on my motherboard.

-ej