An attempt to recover the z-side of L2M3B has been made by modifying the data receiver circuitry on the HDI Link Card reading out this module (HDI Link Card no. 14).
Normally, the data lines are received by a 10114 line receiver chip differentially. The idea for the DATA_RIGHT lines is to cut the non-functioning, i.e. shorted input (DATA_RIGHT-) loose from the receiver input and to apply a suitable reference voltage to that input instead (about 4.0 V). The reference voltage is derived from a voltage divider. (Note: The levels of the AToM signals measured at the receivers are about 4.2V for "1" and 3.7V for "0")
The exact schematics of the changes (done by Max, who also figured it
out, thanks !) can be found here
(ps).
It shows one modified and also an unmodified channel for easy comparison.
The modifications concern only channel 1 (the upper one) p-side, DATA_RIGHT receiver.
I left a label on the card's front panel to indicate that this is a "special" one.
If you ever want to get rid of the modifications, just take off all the axial lead resistors and extra wires, put the 50 Ohm termination resistor for DATA_RIGHT- back on its pad on the solder side of the board, and reconnect the cut pin 9 of the 10114 via a wire to its thru-hole.
5/8/99 Ariane