I have two Farallon PN590a-TN NuBus ethernet cards that only have coax and AUI connectors, and I was curious if it would be possible to add 10base-T support by populating the empty spaces on the board. While it is easy enough to pick up cheap AUI 10base-T transceivers on eBay, they often don't mechanically fit well with NuBus slots. AUI 10base-T transceivers are also not typically very power efficient, having a 5V series regulator running off the 12V AUI power.
I'm also thinking this could be a good proof of concept for modifying cards that don't have AUI, like LC PDS ethernet cards.
Here is a schematic I made of the relevant sections of the card:
Curiously R39 and R43 were missing on one of the cards, which seemed like they would be necessary for automatic media switching. I tried switching the jumper to Auto, and sure enough AUI didn't work. Using a 26LS32 to detect 10base-T link pulses has been problematic on other cards, causing compatibility with Auto MDI-X, so I decided it would be better to just go with completely manual media selection anyway.
Other than the automatic link detection, the rest of the 10base-T circuitry is pretty much straight from the DP83902 datasheet:
One of the boards already had a 4.7K resistor populated for R6, so I went with another 4.7K resistor for R32. The board with R6 also had R26, R27, and R29, so less soldering was required for that one.
Looking for the parts needed, the one component needed that doesn't seem to be readily available is Y2. After some hunting around, I found someone selling the 20F001NG in lots of 5 on eBay for US$4.43 + US$2.78 shipping from China. I already had 4.7K resistors, as they are a common value. Everything else I got from Mouser:
Ethernet jack $0.74 each
Dual LED green and yellow $1.12 each
0.01uF capacitors $0.92 for 10
66.5 Ohm resistors $0.45 for 10
806 Ohm resistors $0.45 for 10
274 Ohm resistors $0.45 for 10
Once the components arrived, I started preparing the board, unbolting the NuBus bracket. I then removing the old components used for automatic media selection, Q1, R41, R44, Q2, R39, and R43. Next used solder sucker to clear the holes for D1, J1, Y2, and pins 13 and 14 of U23 for a wire link. I removed the socketed RAM and ROM chips to give more clearance to R32, then used solder wick to remove the solder from the pads for R32, R6, R25, R26, R27, R28, R29, C24, and C38.
As a first step, I installed R32 and D1, put the RAM and ROM chips back, and then installed the board in a computer and checked that the yellow LED blinked with ethernet activity when using an AUI adapter. I then installed the rest of the surface mount components, then Y2, J1, and a wire link between pins 13 and 14 of U23. Here is what the board looks like with all the components installed:
Installed the board in a computer, connected ethernet, and success!
Now I just need to modify the NuBus bracket, drilling holes for the LEDs and a square cutout for the RJ45.
I'm also thinking this could be a good proof of concept for modifying cards that don't have AUI, like LC PDS ethernet cards.
Here is a schematic I made of the relevant sections of the card:
Curiously R39 and R43 were missing on one of the cards, which seemed like they would be necessary for automatic media switching. I tried switching the jumper to Auto, and sure enough AUI didn't work. Using a 26LS32 to detect 10base-T link pulses has been problematic on other cards, causing compatibility with Auto MDI-X, so I decided it would be better to just go with completely manual media selection anyway.
Other than the automatic link detection, the rest of the 10base-T circuitry is pretty much straight from the DP83902 datasheet:
One of the boards already had a 4.7K resistor populated for R6, so I went with another 4.7K resistor for R32. The board with R6 also had R26, R27, and R29, so less soldering was required for that one.
Looking for the parts needed, the one component needed that doesn't seem to be readily available is Y2. After some hunting around, I found someone selling the 20F001NG in lots of 5 on eBay for US$4.43 + US$2.78 shipping from China. I already had 4.7K resistors, as they are a common value. Everything else I got from Mouser:
Ethernet jack $0.74 each
Dual LED green and yellow $1.12 each
0.01uF capacitors $0.92 for 10
66.5 Ohm resistors $0.45 for 10
806 Ohm resistors $0.45 for 10
274 Ohm resistors $0.45 for 10
Once the components arrived, I started preparing the board, unbolting the NuBus bracket. I then removing the old components used for automatic media selection, Q1, R41, R44, Q2, R39, and R43. Next used solder sucker to clear the holes for D1, J1, Y2, and pins 13 and 14 of U23 for a wire link. I removed the socketed RAM and ROM chips to give more clearance to R32, then used solder wick to remove the solder from the pads for R32, R6, R25, R26, R27, R28, R29, C24, and C38.
As a first step, I installed R32 and D1, put the RAM and ROM chips back, and then installed the board in a computer and checked that the yellow LED blinked with ethernet activity when using an AUI adapter. I then installed the rest of the surface mount components, then Y2, J1, and a wire link between pins 13 and 14 of U23. Here is what the board looks like with all the components installed:
Installed the board in a computer, connected ethernet, and success!
Now I just need to modify the NuBus bracket, drilling holes for the LEDs and a square cutout for the RJ45.
