[Elecraft] KIO2 troubles

[Nate Lewis]

<resending in plaintext, sorry if it dupes>

after many years away, hello again -


I'm trying to get my K2 back online, with a KIO2 in it.  (I have a KAT100-2+K2/100 in a separate box, disconnected for now.)  I'm pretty sure all this worked when I put it away - ten years ago maybe.


I'm using PuTTY in Windows (with a brand new untried USB/RS232 adapter), set 4800/8/N/2 with no control.  From the "port on" menu, the display button gets me a "FA<vfoA>;" in putty as expected.


However, I can't get communication going the other way.  I've doublechecked the cable pinouts and.  Digging in, I see signal coming in to KIO2 U1 pin 6 (MAX1406's R3IN), but always 1.4VDC at R3OUT. :(


Disconnecting RS-232 and measuring: at the 1406, Vdd is ~13V, Vss is -3.8V (hmm...valid, but unexpected), and Vcc is 1.2V (!), matching the output from the 7805 (!).


I lifted the output pin from the 7805, and it shows 5V again, so...something else on the KIO2 is pulling it down, but what?  I don't understand the derivation of Vss or what's inside the 1406, so I don't know where to go from here.


Advice?  Thanks!