Kenwood TS-830S - Bandswitches

A customer came to us with this Kenwood TS-830S right out of the 1980's.  This hybrid radio isn't something we see everyday.  It is clean and well cared for, however the band switch failed to select the 40 meter band with any reliability.

There are lots of notes on how to do this, so I won't go into a lot of detail since someone else has documented this procedure very well.  https://www.k4eaa.com/bandswitch.html

• Pull the final tube nearest the center of the radio, and the driver tube.
• turn the bandswitch to 160m and loosen the setscrew
• turn the bandswitch to 30m and loosen the setscrew
• pull the shaft straight out
• unsolder the 3 wires, and disconnect all connectors
• undo the mounting screw and pull the board out.

Suffice it to say that the band switch contacts were not well attached electrically to the board traces.  Many were corroded, or had loose rivets.  I saw suggestions on how to attach them with conductive paste.  This didn't seem like a good solution, when solder is king!  One contact was pretty badly twisted, so that had to be addressed with some fine mechanical adjustment to get it just right.

A fine diamond-tipped engraver was used to clean the corrosion from each contact, rivet, and trace.  It was then easy to flux and solder the contacts directly to the board trace.  I fixed EACH and EVERY contact in ALL the bandswitches, not just one.  They would all eventually all succumb to failure if left alone.  Each switch contact slider was treated with De-Oxit and checked for continuity.  This fix will outlast the rest of the radio.  The plastic parts have already begun to crack.

The RF board wasn't too hard to take out, but there were three wires that had to be unsoldered.  One was hidden under the board.  (Thanks a lot Kenwood!)

All back together and right on frequency.

TS-440s VCO potting

This Kenwood TS-440s was reported to have PLL issues.  After doing some research it was discovered that the potting material in the VCO was prone to turn conductive after many years.  This throws off the VCO especially in humid environments.

The repair is relatively easy, but labor intensive.  The top cover is removed and the first board flips up out of the way.  The board underneath only has a few connectors and comes out of the case rather easily.

The can around the VCO is best removed to perform this repair.  A few quick turns with the desoldering tool and the can can be separated from the board.  The potting material adheres to the can, but a dental pick can be used to pull and pry and material away gently.  The adjustable transformer also had to be removed to get the potting material out from underneath it.

They say there is better life through chemistry and the proof is here.  The potting material residue on the can was the perfect test subject for what chemical would be best to dissolve it rather than trying to pick it out a little at a time.  It turns out that ordinary brake cleaner softened the potting material back to a jelly-like state, but did not hurt the components on the board.  Dark places around certain components lead me to believe that this was the more overheated and more conductive material.  It was harder to remove and took more scraping with the dental pick.

When all the potting material was removed, the can could be soldered back in, and the radio re-assembled.

A quick test with the SDR proved that the transceiver did not drift when connected to a dummy load.  An on-air QSO confirmed that the audio was good on TX, and listening to WWV confirmed that the alignment was good for RX.