Recently I got a Cabletron EA412 from Philip Zimmerman. The EA412 is
twisted pair only, but I have cheapernet at home. After opening the
EA412 I noticed that it should be possible to convert it to an EA419
by putting some missing parts on the PCB.

I used an old HP Jetdirect EX J2382 (I have another one, does anybody
know where to get new ROMs to make it speak TCP/IP?) and a dead SMC
Elite Ultra to get the necessary parts.

The SMC board provided me with an BNC connector and a FIL-Mag 108.
The Jetdirect gave me an 83C92A and a 5V to -9V DC-to-DC converter.
I soldered the FIL-Mag to T1 and the 83C92A to U1 (I head to unsolder
the TP port to do this). I connected the DC-to-DC converter to U2 with
some wires.

DC-to-DC on the Cabletron (top view):
----------------- PCB-Edge
     (1)  (2)
TP              BNC
     (3)
          (4)

(1) == GND-9V
(2) == 5V
(3) == -9V
(4) == GND-5V

Jetdirect DC-to-DC (seems to be an often used converter):
+-----------------------------------+
|(a) (b) (c) (d)         (e) (f) (g)|
+-----------------------------------+

(a) == GND-5V
(b) == GND-9V
(c) == -9V
(d) == ???
(e) + (f) == Switch???
(g) == +5V

I connected (a) to (4), (b) to (1), (c) to (3), (e) to (f) and (g) to (2).

Now I put parts on D1 (I used the diode from the SMC board), R2 (1k@1%
from the SMC board), R4 and the two resistors beside R4 and R5 (all
0.5k, from the SMC board). I also soldered a C on C14 (I just used the
one that was sitting between  the same pins on the SMC board).

After doing that I connected the board to my cheapernet and it worked fine.
I'd still like to know what to put on C18, R9, R10, R12, R8, C17, R7,
C19, C33, R6 and C13, but the board seems to work without these parts
as well. Anyone out there with a real EA419 willing to open his box?

Matthias
-- 
leo@dachau.marco.de			in real life: Matthias Pfaller
marco GmbH, 85221 Dachau, Germany	tel: +49 8131 516142