Re: µB K1 Relay, RF Side


Had to replace my K1, also.  A couple observations.

Lead free solder SUCKS for desoldering.  Pre-wetting it with a little 60/40 makes it flow a bit easier onto solderwick.

If it happens once, it will probably happen again.  The more you work a board, the more likely a trace WILL lift, or a through-hole will disappear.  Instead of soldering in the replacement relay (which may or may not fail again in the future), I used a dip socket.  Before the arguments against because of added lead capacitance, etc., it works, the radio is happy with it, so I'm happy with it.

On 8/22/2018 9:43 PM, Arvo W0VRA via Groups.Io wrote:
Good Evening, All.

My K1 relay was getting intermittently sticky on TX, so I decided to replace it.  I used an AXICOM with the same pinouts as the stock Hongfa.  I'm not very good at desoldering and tore up some of the pads on the board. A little finagling and everything on the DC side of the relay seems to be working. The connections labeled TX on the schematic are getting 12V, and the connections labeled RX are getting 12V when they're supposed to and 0V when they're not supposed to.
But it's not transmitting.  After studying the schematic for what might be a problem with the new relay install, I'm wondering what's the purpose of the RF side of K1?  It appears that when T/R is off, then the signal from the BNC connector center goes through K3 and through K1 to the first set of filters, and so on.  When T/R is high (5V from the Raduino signalling for transmitting), then K3 disconnects the received signal trace from the BNC connector.  K1 grounds the trace coming from K3.  Is this to prevent transmission RF energy from bleeding into C80, causing some potentially nasty feedback? 

And what would this have to do with the rig not transmitting?  The antenna signal is getting into the receive section, because RX appears fine.  If I'd done something wrong and K1 wasn't interrupting the path from K3, then it should transmit anyway?

Am I missing something?

It's possible I damaged one of the delicate toroidal transformers I suppose.

Any ideas will be appreciated!



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