My friend and I were finally able to dig into my TRC-931 to try repairing the band selector and function switches.For each of these two switches the actual post the outside knob fits on have a pinion gear at its other end.This goes into an elongated metal box which is soldered to the circuit board.The side of it facing the circuit board is open.We had to unsolder this assembly from the board to get to the pinion,toothed slider rack and the piece which is slid by them.The piece the toothed rack actually slides is form molded to the shape of the boards jumpers and push these jumpers back and forth to their different contact points depending on which function you desire.

The first thing we noticed after detaching the elongated metal housing was that the toothed pinion gear at the end of both switches poles were broken into several pieces.We were actually able to superglue these pieces back together to have working pinion gears.Then we tried to figure out why these pinions would have broken apart in the first place.As it turns out,the actual jumpers which slide along the boards contact points are made of very malleable copper.If these become misaligned while sliding and don't self correct their paths,they are in danger of jamming against the edge of the next contact point deforming and destroying the jumper.When this happens the poor soul turning the switch just puts more force into turning it.This extra pressure exerted against the jammed jumper then breaks the pinion gear into pieces.Evidently the shape of these jumpers must be pretty precise for all this to work reasonably well.Unfortunately though there is just enough play in their design to allow the soft jumpers to not always track their course perfectly.Though they may make it most of the time,it only takes one uncorrectable jumper and contact point collision to cause this damage.Here is a picture of the boards jumpers and contacts:

For the band selector switch:



For the function switch:



Unfortunately the jumpers are very thin and tiny with a special shape.The problem with fixing the boxes original switches is that this could happen again.I figure that an old Lasonic TRC-931 which still has good switches has probably just not been used that much.Everything I see points to this problem being an eventuality with all of these boxes.To put it bluntly,these switches were designed to eventually fail.Our next action plan is to try and find new switches with a more robust design to replace the old ones.Hopefully we can come up with a workable solution without having to modify the appearance of the box.

Very strange construction from LASONIC!
This will be one of my next works, to look inside.
Thanks for posting!

Its not lasonics fault, they don't manufacture the original switch and like every product developer, you buy what is available at the time of design.

Also, those clips are only part of the equation, if I recall, there is also a 90 degree gear mesh that moves the sliders up and down in a 931 that breaks, loses teeth, or just plain cracks in half.

But since most electronics have a shelf life of maybe 10 years, its not surprising to see the rapid decay of a poorly maintained bbx.

It sucks, and there are virtually no replacements for it.....

good thing the trc975 has the push button switches

quote:

Originally posted by kittmaster:
...Also, those clips are only part of the equation, if I recall, there is also a 90 degree gear mesh that moves the sliders up and down in a 931 that breaks, loses teeth, or just plain cracks in half.

The soft metal jumpers will jam causing the person turning the switch to twist really hard to get things going again.This extra torque on a jammed jumper eventually destroys the pinion if turned hard enough.Its the jumper/contact design thats the root of the problem,not the pinion.