[Elecraft] KIO2 connection with computer

[Mike S]

At 05:26 PM 11/7/2004, Pierre Vallee wrote...
>In doing the voltage checks for U1, I find readings of 12.77v on pin 5 (should be -8) and 0v on pin 12 (should be 5).  I believe the circuit diagram shows these pins being part of the transmit circuitry (pin 2).  Could U1 be my problem?  Any suggestions.  Thanks


U1 is an EIA-232 transceiver. It converts TTL level to EIA ("RS-232") levels. The voltages you describe show it is operating correctly - when pin 12 is at 0, pin 5 should be more than +3 positive ("space" level). When pin 12 is at 5, pin 5 should be more than -3 negative ("mark" level. You'll notice it also inverts the signal. When idle, the EIA-232 output should be "marking time," or at a negative voltage.

Your problem seems to be that the signal going to pin 5 is incorrect. It should sit at a high level, and pulse low when the K2 is transmitting data. Since it's low all the time,  I would suspect a wiring problem (this single goes through the internal cable to the header connector which plugs into the control board.) Check for shorts to ground, or a lack of continuity from U1 pin 12 to header pin 3.