[Heathkit] DX-40 Keying trouble

[Glen Zook]

Although generally reliable, disc ceramic capacitors can become leaky and even go "short".  A few days ago I had an RME-6900 receiver on the bench with several absolutely burned out resistors.  The source of the problem was traced to the 57 kHz i.f. sub-chassis where a disc ceramic capacitor had gone absolutely short!  It showed less than 0.2 ohms to ground from the B+ line.  Another similar capacitor had less than 5 ohms across it.  Considering that it is a "pain in the posterior" to remove the sub-chassis and then the shield around it, I replaced all seven of the disc ceramic capacitors in the assembly.

Remember, Edsel Murphy NEVER takes a vacation!

Glen, K9STH

Website:  http://k9sth.com


--- On Mon, 8/30/10, Mike McCarty <Mike.McCarty at sbcglobal.net> wrote:

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.