lester@infonode.ingr.com (Lester Bartel) (01/31/91)
> From: rte@cbnewsi.att.com (ralph.t.edwards) > > Last year lightning zapped my house, probably through the power line, > several pieces of electronics croaked, but not (I thought) the > computers, which were on surge arresters. The modem was not on the > same surge arrester as the computer (not enough plugs) and was zapped. > It was still under warranty, so I got it fixed. > The fix was a transister like object near the AC input. > But, although the modem works fine on other computers, > it does not work with my plus, to which it was attached at the great zapping. > So, here are the questions: > > 1. Both serial ports work with the printer, neither see the modem. > What lines are used by the modem that aren't used with the printer? > > 2. What symptoms should I look for with my RS-232 tester? > > 3. If I conlude that the ports are zapped, can one or two ICs > be replaced, and where are they? > > 4. I haven't opened up the plus yet, although I plan to soon. > It's 13 months old. Do they use surface mounts or what? > > I'm a reasonably competent tinkerer, and have opened my older mac > several times to fix problems, add upgrades etc. > Please reply by mail I had a similar experience on my Mac 512KE, though I can't blame lightning for sure. I simply replaced the RS422 driver chip (a 16 pin dip). One of the Inside Macintosh manuals has a block diagram of the serial port circuitry (amoung other ports), and I used that as a guide to determine which chip was likely fried. BTW this only affected my modem port. I also had a problem (don't know if it is related or not), where the receive + pin appeared to be capacitively tied to the receive - pin. This would cause the RS422 receiver to not recognize a difference between the two inputs. I simply tied the receive + pin (unused for RS232) to ground and the printer port now works like a champ. - Lester -- Lester Bartel b23b!naomi!lester@ingr.com Dasix, An Intergraph Company uunet!ingr!b23b!naomi!lester