[R-390] Offset gear source Pass_2 Band switch

[Flowertime01 at wmconnect.com]

ED, KØBKA,

You ask about the RF band switch.

The TM implies you can set the band switch with a meter from the top side 
without pulling the RF deck. Resist the urge to set your receiver with this 
expedient field procedure.

Pull the RF deck and set the band switch by eye ball of wafer switch sections.

Unless a section in your band switch will not align resist the urge to change 
its mechanical position. You may need to change the mechanical position of a 
switch section in the RF band switch assembly if a contact has been burnt or 
someone did something best not spoken of some where in the past.

If you feel the switch does not roll over to its next position on the MC 
change like it should there are things to adjust. The switch should roll over to 
its next position like it should on the change of the MC knob from one detent 
stop to the next detent stop. every band switch change going up or down in 
frequency. If you have to move the MC knob past the detent and then back to get a 
band change, then some adjustment is in order.

Likely all that is needed is a resetting of the band switch shaft and clamp. 
But study the gear train and split gears near the band switch. Get an 
understanding of the gears between the MC knob and the band switch. If the band switch 
works fine one way but not the other. As it works nice going up but not down 
or going down but not up you may want to move a the mesh of a gear pair over 
one tooth one way or the other. But before you do that pull the deck and check 
the switch shaft and clamp to see if you can get a good operation by simply 
adjusting the shaft angle in the band switch shaft clamp. A small change of only 
on degree of 360 in rotation one way or the other of the band switch shaft 
can bring a vast improvement in the switch function.

The problem is the several wafer sections of the switch are spread over 6 
inches of switch shaft. Rotational torque from one end of the shaft to the other 
allows the sections near the front clamp end of the shaft to get more rotation 
than the sections on the far end of the shaft. The back end sections get left 
behind. Going up the dial or down the dial and changing bands has a different 
lash. 

Over the years the many operations have worn the hole in each wafter section 
a bit. So now there is also a bit of extra play between the shaft flats and 
the wafer section.

If you feel you just need to do something about that resist as long as you 
can. You can undo the clamp and slide the shaft out of the clamp by a 1/2 inch 
or so. You can then add a coat of glue to the shaft flat to build up the flat a 
bit to reduce the play when you put the shaft back in place. better to build 
up the shaft to fit the hole in the wafer than to try and build up the wafer 
section. Glue on rod is not like extra glue in switch section to remove.

In doing the visual alignment you have six wafer sections, six switch 
positions, the mesh going up, the mesh going down and the contact area of each 
contact.

You want to move the switch through all the positions and watch each contact 
going up the dial and down the dial. Just a little bit of change will put a 
switch into or out of good operation. As the switch wears over 50 plus years 
that sweet spot of good operation gets to be a much smaller range.

Poor alignment lets a switch just barley make contact. That small area of 
contact has to carry the current. This small contact area may burn. After the 
burn the switch is missing some contact area. And the adjustment more critical.

I have seen many burnt switch contacts. I have never seen a switch so messed 
up that it could not be adjusted to give good operation as expected. I have 
not seen every R390 and R390/A and these receivers are getting older all the 
time. You could have a RF switch that may need more than some alignment of the 
shaft in the clamp gear. But before you venture down that other repair 
procedures, try to do the adjustment by pulling the deck and looking at what you are 
adjusting.

I hope all this helps you get your switch back into good alignment. It is 
fairly easy to do. It just takes the time to pull the RF deck. It may feel like a 
lot of work but is easily completed in under 4 hours of real time.

Roger AI4NI   </HTML>