[Heathkit] DX-40 Keying trouble

[Mike McCarty]

rhulett1 at comcast.net wrote:
> Recently acquired a tired old DX-40 with keying issues.  SlightÂ
> frequency change after key-down ( chirp ), now sometimes will not
> stop oscillator on key up.  I'm suspecting the 0.02 bypass caps (
> C4, 10, and 44 ) on the keying line, but can't imagine a failure mode
> that would be intermittent for these disc ceramics.  Advice?

My first piece of advice is not to rely too heavily upon
your imagination. Electronics devices are capable of failing
in ways which sometimes defy imagination. Imagination is
a good thing to have when troubleshooting, especially if
it's a wild one. It does have its limitations.

Ceramics do sometimes short. I've seen just a few. You
likely won't be able to find such a short with an ohmmeter,
until it's so bad that your finals are smoking from constant
key down. If you have a real cap checker which can measure
leakage resistance in the Gigohm range, then you can use
that. OW, just replace the caps. They're cheap. If the
problem persists, then look for other causes.

Mike
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