On Microphones, Part 2

My Astatic D-104 microphone arrived in the mail today.  My wife posted on Facebook that, since I got my radio and started collecting additional bits for it, "Mike awaits the mailman more eagerly than a grumpy dog."  I opened it up and looked at it.  It even has the right 4-pin plug on it!

The first thing I did?  Take the bottom of the base off, of course.

Look at that, they even included a wiring schematic in the bottom:

So, I started poking around with my multimeter.  At first I couldn't make any sense out of what I was seeing.  Then I studied the schematic a little closer.  What is this E-R switch that they mention on the left of the schematic?  It looks like if it's set to R, then contacts 5 and 6 (red and black wires) will be connected together when the switch is pressed.

A little internet research showed that E-R means "Electronic vs Relay".  My radio definitely wants this set to Relay.  Ah, here's the switch, on the board containing the volume control - and mostly hidden under some wires.  Looks like it's set to E.

I switched it to R.  Then, when I closed the "grip-to-talk" switch, the red and black wires from the cable (contacts 5 and 6) were indeed shorted together (as indicated by zero resistance on my multimeter), which my radio will see as Push-to-Talk.

OK.  Since my mic has the right Kenwood 4-pin plug on it, I can only hope that it's wired correctly.

It works at one end of the cable; how about the other end?

So, I start by plugging my multimeter into two holes on the plug and push the grip bar.  Nothing.  I try a two more holes.  Nothing.  No combination of holes indicates zero resistance when I push the grip bar.

I sense a problem.  So, the next step is to trace each of the wires from the one end of the cable to the other.

First of all, I find out that it's not the correct pinout for my radio:

The audio is on pins 1 and 2 instead of pins 1 and 4.  It looks like I might be re-soldering (or replacing) the connector.

Second of all, I find out that pin 3 is not connected to anything.

So, it's time to dig deeper.  I removed a couple screws from the clamp on the cable and then unscrewed the connector to get at the solder connections on the plug:

I start testing both ends of the cable with the multimeter.  Bad news.  The black wire is broken somewhere in the cable.  For this wiring problem, I can probably hack something temporary together before finding a replacement cable - even just running a separate "black wire" into the plug for the PTT connection for now.

Also, I noticed that the grip-to-talk bar doesn't always "release" its connection upon releasing the bar.  This can probably be fixed by cleaning/aligning the switch contacts in the stalk (according to various internet posts).  If I can figure out how to get the crazy thing apart!  It looks like I would have to start by unsoldering the 4 wires for the cable and the 8 wires coming down from the stalk.  (I have to unsolder the cable because one of the 8 wires from the stalk is soldered to the E/R switch - on the bottom side of a metal plate where I might not have enough access without removing the cable.) Then, after that, I think it gets fun!  Something about "take pictures" and "don't lose the teeny screw" and such.

"Caveat Emptor" indeed.  My wife's suggestion?  "You're likely to get screwed on eBay.  You should probably buy things like this at a hamfest where you can at least see them and maybe try them out first."

Good advice!  Her clear thinking is one of the key things that drew me to her over 25 years ago. :)

I'd hate to think that I'm just out the $45 (plus shipping), so I'll try to get this working.  

73, and thanks for following along!

- Mike, K9MJA