The NuBus Media 100 system was initially produced for the PowerMac Quadra 840AV. When the PowerMac 8100 was released, Data Translation Inc. provided an upgrade service to make the earlier cards compatable with it. The cards I have, have some post-production modifications that MAY indicate they have been modified for 8100 compatability. I do not know if that is what the modifications are for or not. I have obtained a pair of card with a newer revision, without modifications, and they work fine in my Radius 81/110.

For orientation, I'll use these terms.
Front of board. The side the connectors are mounted on.
Back of board. The side the connectors are not mounted on.
Top of board. The edge with the two interconnect cable connectors.
Bottom of board. The edge with the NuBus connector.
Rear of board. The end with the mounting bracket and external connectors.
Fore of board. The end towards the front of the Macintosh.

The Cathode end of a diode has a band, dot or otherwise marked.
The Anode end of a diode is not marked.

Schematic representation of a diode.
AnodeCathode

For soldering, I like the 15 watt, blue handled Radio Shack iron with the three wire, grounded cord. The tip is very small and able to be used on small and tight connections.

DISCLAIMER: I DO NOT WARRANT OR GUARRANTEE IN ANY WAY THAT THESE MODIFICATIONS ARE FOR POWERMAC 8100 COMPATABILITY! IF YOU TRASH YOUR MEDIA 100 CARDS BY USING THIS INFORMATION, IT IS YOUR FAULT, NOT MINE. I'M NOT FORCING OR COERCING YOU TO DO ANYTHING.

Let's start with the Processor card. I assume it's called that because it has a Motorola MC68EC030FE40B 40Mhz 68030 CPU in the upper left corner of the front side of the board.

On the front side of the board, two diodes have their anode ends soldered to the bottom end of L4 and two diodes have their cathode ends soldered to the bottom end of L5. L4 and L5 are right at the rear end of the NuBus connector. The marking for L4 is visible, for L5 it is not, but it has to be L5 because L1 through L4 are marked and there are no other inductors on the front side.

These diodes have the other ends soldered in pairs, one each from L4 and L5 connected together. A wire is connected from one diode pair to pin 11 of the audio input connector at the rear and another wire connects the other diode pair to pin 13 of the audio connector. 11 and 13 are the bottom two pins at the very bottom, foremost row of the audio connector so there should be little difficulty soldering the wires.

On the back side of the board, the diode setup is similar. Two diodes have their anode ends soldered to BOTH pin 1A and 1B of the NuBus connector. A is the bottom row, B is the middle row, 1 is at the rear. Two other diodes have their cathode ends soldered to the bottom end of L5. The connection is easy to identify as the L5 lead comes through right in the middle of a square formed by the leads of C100, C101, R33 and R34.

These diodes have the other ends soldered in pairs, one each from NuBus and L5 connected together. A wire is connected from one diode pair to pin 24 of the audio input connector at the rear and another wire connects the other diode pair to pin 26 of the audio connector. 24 and 26 are the two bottom pins of the second row from the rear of the audio connector.

The audio connector pin layout has the odd numbers 1 through 13 on the foremost row, even numbers 2 through 12 on the next row to the rear, even numbers 14 through 26 on the third row and odd numbers 15 through 25 on the rear row.

That is the extent of the VISIBLE modifications to the Processor Card  12004 MEDIA100-1 PROCESSOR REV.1B (or maybe 1D, the dot matrix printer they used on these lables was lousy, with 3x5 dot matrix characters, but it looks more like a B to me) indicated by the lable on the back side of the NuBus connector.
If your card's revision number does not match this EXACTLY, then you should not attempt the modification.

Now for the  Video card. This is the card with the large Raytheon chip near the rear on the front. This card is where the video input and output is done.

On the front side, a plain insulated wire is connected between pn C3 of the NuBus connector and the fore end of L15. Immediately below L15 you can see two traces that turn at right angles towards the top of the board. These traces have the solder mask scraped off and a short length of bare jumper wire soldered across them.

Next, two diodes have their anode ends soldered to ground, the bottom mount point of the video connector at the rear. Unfortunately, the connector's pins are not numbered, but it's easy to find where to solder the cathode ends. One connects to the bottom-most pin, the other connects to the third one up from the bottom. You can't connect to the wrong row because you just can't get to any other row without bending things.

On the back side, one diode has its anode end soldered to the bottom-fore pin of the video connector and a second diode has its anode end soldered to the third pin up, same pins as on the front. A third diode has its anode end soldered to the bottom pin of the middle row and a fourth diode has its _cathode_ end soldered to that same pin. This diode has its anode end connected to ground, the lower mount point of the video connector.

The three diodes with their anode ends connected to the video connector all have their cathode ends soldered together then connected with a plain insulated wire to the rear end of R236.

That is the extent of the VISIBLE modifications to the Video Card  13166 MEDIA100CR-2 REV.14  indicated by the lable on the back side of the NuBus connector.
If your card's revision number does not match this EXACTLY, then you should not attempt the modification.

I can't tell what exact type of diodes they are without removing one from the board, which I'm not going to try. They all appear to be the same type.