Ref: 09330012
Title: Etherlink/mc on the PS/2; electrical problems
Date: 7-21-88

Copyright 3Com Corporation, 1991.  All rights reserved.

Customer seems to be experiencing an electrical problem when they
use Etherlink/MC with Thick cable (DIX connector) on a bus MCA.

Normally the IEEE 802.3 (like our adapters for PC) need 0.5A /
12V.  Olivetti told me that an IBM PS2 Bus MCA gives you only
0.175A / 12V and 1.6A / 5V.

Answer:

There are I believe 5 slots in the PS/2 each allowed 0.175 A. That
amounts to 0.875 A, more than enough to use an external transceiver,
provided that there is no conflict with other boards in the PC.
Very few boards use 12V, memory boards for instance do not, so in most
cases there is no problem.

Please note that the PC has also similar 12V amperage limitations, but
it does not seem to be a problem.

Possibility that the customer is experiencing fuse blowing
problems.  Many external transceivers suck a lot of power during
initialization due to their large internal capacitors.  Pulling
that much power through our MC adapters blows an onboard fuse.
We don't have this problem with our external transceivers, as
ours aren't so power hungry.

The suspect fuse is located to the right, and a little below the point
on the MC board marked as TP3.  TP3 is locate at about the center of the
board.  This is assuming you are looking at the board with the edge
connection down, and to the right.  The fuse looks much like a resistor.
It is a fast blowing fuse and cannot handle the demand of power the
external transceiver is requesting.

When we receive a board with this fuse blown, we replace it with
one that can handle the initial voltage surge.  The replacement
does not resemble a typical resistor.  It is a polymer type fuse.
Don't be confused by this.  You should be able to locate this
replacement fuse locally.
