[Elecraft] Radio Troubleshooting

[Don Brown]

Hi

There at least 2 good methods of troubleshooting a radio (or any other an=
alog circuit). One is signal tracing and the other is signal injection. S=
ignal tracing is good when a circuit is a generating device such as a tra=
nsmitter. In this type of circuit the device provides a signal internally=
 to trace with an indicating piece of test equipment. This would be somet=
hing like a RF probe and DMM or a wide band scope. The approach should be=
 to split the circuit in half and make a test to see if the signal is the=
re. If not then split the half in half and make another test. If the sign=
al is there at the one half point then go forward about another 1/4 of th=
e circuit and make another test. This should get you to the failed circui=
t quickly.

The other method is the signal injection technique. In this technique a s=
ignal generator is injected a various points in the circuit and you look =
or listen for an output. This works on amplifying circuits like audio and=
 RF, IF amplifiers. The one half method from above works here also except=
 you are providing a signal at the test points and in the case of a radio=
 you listen to the speaker for the signal. This is the method described b=
y Tom on the Elecraft website under Quick and Dirty Signal Tracing. The a=
ntenna signal source is good (and cheap) but I find a noise generator is =
more convenient. You can make up a probe with a length of RG-174 cable wi=
th a small value capacitor in series with the probe tip similar to the K2=
 counter probe to connect to the noise generator (or you can use a scope =
probe). Then touching various test points in the radio with the probe sho=
uld cause a loud hissing noise in the speaker or phones. Because the sign=
al is broad band noise it will drive any circuit from audio to VHF even i=
f it is a tuned circuit.

Once you have the circuit stage isolated then get out your DMM and magnif=
ying glass and look for bad solder joints, missing or wrong value parts o=
r open, shorted or bad parts in that order. If you have isolated the circ=
uit there will usually be only few parts to look at as a potential proble=
m

The K2 has a number of test points built in to make these tests. They are=
 the "W" jumpers for the options. For a receiver problem I would start at=
 W3 first then W5 then W6 then W1 and the antenna connector last. When th=
e signal is lost then go back a little to isolate the bad circuit.

Digital circuits need a little different method but that's another story =
;-)

I hope some of you find this useful


Don Brown
KD5NDB


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