Roger Weichert wrote:
> One device goes between one of the RS422 comms line and ground and the
> second one goes between the other comms line and ground.
>
> They look just like resistors, but obviously are not. They have what
> looks like a glass body with painted on rings. A bit like a large
> 1N4148.
>
> Out of circuit one measures 194 ohm both ways and the other about 35
> Meg ohms both ways. (no fingers)

Assuming you measured this with a normal ohmmeter that puts a volt or less
accross the device, 35Mohm sounds plausible and 194ohm is most likely fried.
I guess they are intended to clamp the lines within some acceptable voltage
of ground.  They are probably TVSs.  You should be able to replace them with
any TVS with a reasonable rating given whatever common mode range your
circuit has to handle.


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