[Elecraft] KAT100 signal question

[Jack Brindle]

Q3 is probably not your problem. It is an open-drain switch that  
inverts the 8R signal, conditioning it for the microcontroller. It  
appears that the MCU provides the pullup for the signal through the  
internal pullup on PB6. 4.99 volts is about right for this signal.

Just what is the "relay problem" you are seeing? If Q3 and the /8R  
signals were bad, the KAT would not switch to transmit conditions at  
all. This would be indicated in a number of ways, such as not even  
trying to tune. Relay troubles, however, could be isolated to a small  
area in the circuit.

On Jul 23, 2005, at 10:37 AM, BobConvers at aol.com wrote:

> In troubleshooting a relay problem on my KAT100, Gary advised me to  
> check the
> signal /8R, generated by Q3.   I think Q3 may be faulty, since  
> (using a Fluke
> DMM) signal /8R alternates between zero and only 4.99v as the  
> KPA100 is
> cycled between receive and TUNE.   Signal 8R alternates between  
> 7.91v and zero, as
> I would expect.
>
> Before, I disassemble, de-solder, and install a new Q3, however, could
> someone verify that 4.99 v is indeed lower than it should be and Q3  
> is probably bad.
>   Thanks.
>
> 73,
> Bob, WO3E
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- Jack Brindle, W6FB
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