[rescue] Serial port? More like serial cable...

[Ethan Hawke]

>> I'll have to investigate further, I believe it's the RS423 drivers
>> that have failed, as both ports fail simultaneously, whereas they can
>> receive but can't send.
> That strikes me as unlikely - by which I really mean, I'm having
> trouble coming up with a plausible failure mode that would lead to
> that.  I would expect that, even if they're in the same package, the
> transmitter circuits for the two ports would be more or less
> independent.
>
> Are the modem control signals driven normally?  I'm wondering if
> perhaps the relevant power (usually +12 and -12, in my admittedly
> limited experience) has failed.

Those are some very good points, the transmitters are all combined in a 
single package (a UC5170),
I attached a logic analyzer before and after the driver and found the 
output was very weak (2-3V),
and not the normal +/-10V it should be (in RS232 mode, +/-6V in RS423 
mode). Turns out the
serial cable had failed. The SS10 clone I first noticed the problem on 
IS bad, so when the same
symptoms appeared on some of my other machines, I made the faulty 
assumption it was the same
thing. One of those unfortunate series of events that lead you down the 
wrong path.

>> Replacing the driver will be difficult, but I may be able to
>> piggyback a replacement on the old one.
> I'd hesitate to try replacing the driver unless you're certain it's the
> culprit.

Indeed, good call. Buying a new serial cable will be way easier :P.

Thanks everyone,
Ethan