Hank,
You might want to check the output of that NPN transistor circuit before
you connect it to the K3 FSK input again.
If there is a base to collector short, it could put the full RS-232
level on the FSK input pin, and that is quite likely to fry something in
the K3 (like that 220 ohm resistor).
That NPN transistor should show open circuit during non-keyed times and
show as a short when it is turned on by the RS-232 signal line. It
should never show any voltage at all in either state.
The base K3 circuits are protected with a series reverse polarity
protection diode (the KPA3 does not because of the diode voltage drop).
However, if the FSK Keying box were connected and powered at the same
time as the reverse polarity event, there could have been some strange
current flow between the K3 FSK input pin and the FSK box. The full
circuit would have to be analyzed to know the answer for certain.
73,
Don W3FPR
On 4/19/2014 3:58 PM, Pfizenmayer wrote:
R2 is open and is blackened like it has been over dissipated . Now the $64,000
question is how can one over dissipate a 220 ohm resistor fed from 5 volts thru
10K ohms ???
Even if there was no resistor fed from 5 v it would be a tad under 1/8 watt -
which is probably on the edge for a 0508 SMD chip resistor . R98 on the RF
board feeding P35 is in fact 9980 ohms and the runner to P35 is Ok. The other
end of R98 shows 4.97 volts from U12 so the 5V regulator is OK . There are
1000 pfd caps to ground from the 15 pin ACC connector before the 220 ohm
resistor so unlikely RF could have done it plus I have a 2.4 inch #31 core with
14 T right at the connector before it runs to the N1MM FSK keying box with the
standard open collector NPN to FSK in.
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