Haunted keyer

[VA2MM]

I recently activated the keyer function on the RRC, and it seems to work well. However, it sometimes works by itself, sending random CW. A hands-free function?  At first I thought it was faulty wiring in my paddle, but no, it even does it when the paddle (and the IO connector) is unplugged from the RRC box.  If I power cycle the RRC, it shuts up for a while, but eventually it sending again.

Anyone else run into an RRC with a CW mind of its own?  If so, how do you fix it?

Mark VA2MM

[sm2o]

The Keyer do not send CW by it self, something must make a connection from one of the inputs to GND. look in the I/O connector or PAD connector if there is something making this connection.

73 de mike

[VA2MM]

Thanks for the comments, Mike.

I attempting a bit of humour about the keyer sending CW by itself but there does seem to be an intermittent problem with the keyer circuit in my RRC control box. There is nothing stuck in the paddle or IO connector.

I've done a bit more investigation and it seems to be a hardware issue in the RRC.  The open-circuit voltage is different between In1 and In2 (or Tip and Ring of paddle connector), which does not seem normal to me at all. In1 (Ring) sits (unkeyed) at 8V but In2 (Tip) drifts between 6.5V and 6.8V. When it's down near 6.5, In2 is very sensitive: just touching the voltmeter probe to it causes it to send dits (even though the voltage is still 6.5V).

So, perhaps a defective clamping diode (D13) is pulling the voltage down, or a problem with the transistor pair DT1. Unfortunately, there is no RefDes silkscreening on the board, so hard to find my way around.

I could probably fix the symptoms by putting a pull-up resistor to 8V, but that could be just masking the root cause problem. What's the warranty on these boxes?

Mark VA2MM
                                                                                                                                                     

[sm2o]

Hi

Yes I guess you have right D11 and D13 is ESD protection diodes, and they can behave like that if they have taken a hit by lightning  for example, we have replaced them a few times before, Not on the Keyer input but on other inputs. You can try by removing the component. I can send you new ones if you are able to replace them by yourself.

73 mike

[VA2MM]

Excellent.

The component layout is very helpful. I'll try removing D13, and if that clears the problem, I'll replace it with a new one. It will probably be easier for me to get the diode array locally than you having to send it.

Thanks again,

Mark VA2MM

[VA2MM]

FYI, replacing D13 solved the problem. I'm sure it wasn't caused by a lightning though because it's at the control end and never left the protected well-environment of my apartment, so perhaps a defective component.

Regards

Mark VA2MM