William Chops Westfield wrote:
Well, thank you all for the quick help! Armed with the possibility that
it might be putting out 9V, I checked out the specs on another chip on
the board, a MTD392. Turns out that the MTD392 is the coax transceiver,
and it specs out -9V as its input. So, the question is, what else on the
card might need 12V? Other than AUI I mean. I gather the manufacturer
wouldn't have put extra traces on the card for no reason. And, if I
don't plan on using coax, can I just forget about the 12V supply? I
guess the only real way to find out is to build my circuit with only 5V,
get it working on the card I have that I know doesn't use 12V, then try
it with one of these other cards. Bleh. I wish there was an easier way.
I suppose I could cut the trace on the board, then toss it into a PC.
Any other ideas?

Thanks!

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
        -Douglas Adams


> This is very likely to be an isolated 5V to 9V DC/DC converter.  I believe
> that cards with an AUI (15 pin) connector will require 12V to power the
> transceiver at the other end of the AUI cable (the requirement for 12V is
> part of the AUI specification.)  Cards with "thinnet" connectors (10base2:
> BNC connectors) use the 5V/9V converter to power the section of the circuit
> that actually connects to the coax (and need to be at least somewhat
> isolated from the PC's power supply.)  A card that does ONLY twisted pair
> shouldn't need 12V OR the DC/DC converter.

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