3 Days of Radio Fun, 1 Day of Radio Repair

Contacts, Contacts, Contacts

From Wednesday to Friday, I had fun on 40, 20, and 15 meters.  I contacted W1AW/4 in Florida on all three bands; I talked to KE7JNT on Vancouver Island on 15 and I talked to CO4LS in Cuba on 20.  I had my first non-net non-friend conversation with KI4UIE in Kentucky.

I've learned to quickly tune up my radio, making notes of what tuner settings work best for each band.  Tuning the radio and the tuner now takes me about 20 seconds.

15 Meter Audio Problem

I had a 15-minute conversation with W1KA in New Hampshire on 15 meters early Friday evening.  He gave me what seems to be the best explanation of my audio problem on 15 meters:  He said that when it was working, I was coming in at 5 to 10 over S9 - but when it cut out, it sounded like I was talking from across the room.  He helped me try a few different things - wiggling the mic wires, wiggling the Drive knob (where I know the bad solder joint is)... but nothing helped.

He had lots of nice things to say about my signal and the radio and the audio quality of the mic (when it was working), and he said that he looked forward to talking with me again when I get the audio problem sorted out.

Digging into the Radio

I decided to try to fix up the known problem with my radio - the visible bad solder joint on one of the air variable capacitors.  I also picked up a can of DeOxit from Radio Shack so that I could clean the dirty volume pot (and all the rest of the pots and switches as well).

I unhooked the power cord and the antenna and the microphone, took the top and bottom covers off - and then I proceeded to take the front faceplate off.  I technically didn't need to do this, but I decided to do it anyway just to see that I could do it.

This involved taking all the knobs off the front of the radio.  Here is what it looked like spread out across the desk, with the knobs and the screws (in an Altoids tin) on the Mac and the front faceplate over to the left.  There's also some tools and some solder wick and some flux and ... well, I don't keep the neatest work area.

After turning the radio upside down, I could spray the DeOxit into the bottom of each of the pots.  I could tell after a couple sprays in the volume pot that it was already turning smoother.  I also went ahead and sprayed every other pot and rotary switch I could get to, including all the wafers on the bandswitch.  I even opened the antenna relay compartment at the back of the radio and sprayed the last (hidden) section of the bandswitch.  Five minutes later, I re-sprayed all the pots and switches again.

After letting that dry for a bit, I took a good look at the repair I needed to make.  In order to fix the bad solder joint, I had to remove a metal shield between two of the coil boards:

If you look closely at the top and bottom of the shield, you will see that each screw is attached to a blob of solder, which is attached to the Heterodyne Oscillator board.  This is so that there is a good grounding connection between the Het Osc board and the shield.  So, my first task was to remove this solder.

I got out my trusty Radio Shack soldering iron.  After about 4 or 5 minutes, I realized that 30 watts wasn't going to make a dent in this solder, even with a bit of flux on it.  So, I got out my trusty PowerProbe butane soldering iron and the "Solder Sucker".  I was able to get enough solder removed from each side with the butane iron and the solder sucker (and a little bit of solder wick) so that I could loosen the screws and remove the shield.

Now I had reasonably good access to the bad solder joint.  I got the electric soldering iron out again and tried to heat up the pin on the capacitor.  Once again, it just wasn't doing the trick.  So, I made a gamble.

I approached the guts of my radio with a butane soldering iron.  Note that this thing gets hot.  The soldering tip has a flame vent where the extra heat escapes; I made sure that this vent was pointed vertically (rather than at either of the coil boards near where I was working).  I put a little bit of flux onto the problem area, heated up the pin and the surrounding solder with the very tip of the soldering iron, and then applied a nice clean blob of solder that completely coated the pin and the surrounding contact area.  Success!

Second Verse, Same As the First

As I looked over my work, I studied some of the other parts of the radio.  I happened to notice a second bad solder joint; this one was on the rearmost air variable capacitor, and was visibly in worse condition than the one I had just fixed:

Thankfully, the nearby shield did not have the grounding blobs of solder on its screws.  It did, however, have a ground jumper soldered right to the middle of one side of it.  After removing the screws, I grabbed the shield with a pair of needle-nose pliers; then I heated the solder with the butane iron until it loosened enough for me to pull the shield out.

Once again, I applied a little flux to the bad joint and resoldered it (again, with the butane iron!).  Then I screwed the shield back in place and re-soldered the ground jumper to it.

That's enough working inside the radio for one day.  I reattached the faceplate and put all the knobs back on.  The reattaching of the knobs was interesting, as I had to try to figure out how to align all the pointers with their appropriate markings on the faceplate, and I had to put the knobs back on in a particular order so that I could actually reach all of the set screws.  This took a few minutes, but I finally got it all back together.

I screwed the bottom cover back on, reattached the speaker connector, and laid the front cover on top of the radio.  I plugged the power cord and the antenna back in, and turned the radio on, hoping to hear the hiss of atmospheric static.

Uh oh.

Instead, I was greeted with silence, except for the sound of the meter needle being pegged all the way to the right.  I was stunned, although not entirely surprised.  I retraced my steps in my mind.  I did make sure not to melt or unsolder any other wires, right?  Yes.  I did remember to pull out that one piece of dried solder that fell out of the solder sucker when I reset the plunger while holding it over the radio instead of over the desk, right?  Yes, I did remember to get that.   I tried flipping the meter switch and the band switch; nothing.  All the while, I was only leaving the radio on for a couple seconds at time, just in case.

Frustration set in.  And disappointment.  And discouragement.  I have been having so much fun getting to know this radio; and I had no idea what I had done to it.

I turned it on one more time and listened.  I thought I heard the faintest bit of sound from the speaker, so I turned up the volume.  And then I absentmindedly turned up the RF Gain.

And the radio came back to life.  Loudly.  And I laughed at myself and shook my head.  The RF Gain acts as a squelch control; it's really handy when listening to loud signals, because it allows you to cut back the gain so that the static disappears.  I usually leave the RF Gain set at 10 so that I can hear even the weakest signals that float slightly above the noise.  As you turn it back, the meter needle moves to the right to show you the minimum level of signal that is being received.

When I had reattached all the knobs on the front panel, I had set all of them to zero so that I could line them up (and get to the set screws so that I could tighten them).  I had never had the RF Gain knob set at zero before, so I did not expect this behavior (complete silence and a pegged meter).  But once I turned it back up, and the radio came back to life, I realized exactly what I had done.  I went to 40 meters and spun the frequency knob, the familiar sounds of lots of conversations (strong and weak) gave me great comfort.

Heating It Up

I decided to tune it up on 40 meters.  I tuned the transmitter into the dummy load, and then I tuned the antenna.  And then I switched to CW to adjust the Load for maximum output.

And my radio was putting out almost 150 watts.  I've never seen a reading that high on the radio.  Could my cleaning and soldering have made that much of an improvement?

I tuned to 15 meters and tuned up there as well - probably about 130 watts.

And then I wondered...

What About 10 Meters?

My radio had been deaf and mute on 10 meters - no receive, and no power out.  I decided to give it another shot.  I turned the bandswitch to 28 MHz and turned up the volume.

And I heard something.

I consulted my tuner manual for appropriate inductor/capacitor settings for 10 meters, and I adjusted the Drive control for the loudest noise.  I then spun through the band - and I heard signals!  I heard Japan calling CQ; I heard lots of digital traffic.

So, I decided to try to tune up the transmitter as well.  Wow, the tuner is much more touchy at the higher frequencies!  But, I got a good match on the antenna and hit CW Send.

125 watts out.  On 10 meters.  Into a 40-meter dipole.  With about a 1.2:1 SWR.  From a radio that was previously DEAD on 10 meters.

Whether it was the two solder joints, or a dirty bandswitch, or something else - doesn't matter at this point.  The crazy thing works and I'm pretty ecstatic about that.

And a New Mic Cable

I had ordered a replacement mic cable from eBay, expecting it to arrive on Monday.  Well, it arrived today!

So, after getting the radio working (and then taking a break), I tackled the mic cable.  I had to search carefully to find out which had a shielded audio cable in it; the one I found actually has an extra wire in it - it is 4 conductors, with one of them shielded, which makes it actually a 5-conductor wire.

I carefully trimmed back the cable on both ends.  The plug was on the "straight" end of the cable, but I needed the straight end of the cable to go into the microphone - so I unsoldered the plug.  (By the way, the electric soldering iron was plenty capable for this job.)  I then trimmed back the cable jacket - about 1 inch on the coiled plug end, and about 3 inches on the mic end.  I soldered the appropriate wires onto the plug and tested them with the ohmmeter; I then clamped the cable into the mic stand and soldered the 4 wires in that end.

The result?  A mic cable that looks like it actually belongs:

I haven't actually had the mic on the air yet, but I have verified that it moves the meter when talking into the dummy load.

Now, I just need to make another contact on 15 meters to see if my audio problem is still present.

All in all, a day of radio repair that turned out good - in fact, it turned out better than expected!

73 until next time!

- Mike, K9MJA