[R-390] More on my new (old) R-390 Zero Adjust

[Flowertime01 at wmconnect.com]

Jim,

The zero adjust knob is a small knob, same as antenna trim and Limiter knobs.
Big knobs are Audio gain and RF gain.
Large Knobs are the MC and KC change knobs.
The knobs come in these 3 sizes.

Zero adjust shaft screws into a threaded bushing.
If the knob sets on the shaft to close to the front plate or the bushing,
It will not allow the shaft to screw in far enough to disengage the zero 
adjust clutch.

Having a wrong knob on the shaft could be part of your problem by causing 
clearance problems.

Also the zero adjust shaft has a large (1 1/2 dia) disk that covers the three 
pins on the zero adjust clutch. This disk will wear off the small pin on the 
zero adjust shaft and the disk falls out of the receiver, As usual once parts 
begin to fall out of any thing it does not work as well as it did before the 
items fell out. Check that the disk is on the end of the zero adjust shaft. Its 
an eye ball inspection once you know the receiver is supposed to have the 
item.

The zero adjust gets turned counter clock wise to engage the clutch and let 
the KC knob run free. Set the dial counter to any XX,X00 number and run the 
zero adjust knob clock wise to a firm stop. This should disengage the clutch. The 
KC know should turn freely a bit through the zero adjust range and not move 
the dial counter. You can force the KC knob at the end of the zero adjust range 
and move the dial counter. Something a good operator would not do.

Set the function to Cal. turn the BFO, set the BFO pitch to zero. Now the KC 
know can be rotated to bring the receiver to zero beat. If the VFO band spread 
is not more than a couple Kilo hertz the calibration of the receiver should 
be good across several hundred KC. You may want to zero the receiver as you 
tune from end to end of the KC band. You may want or need to zero the receiver as 
you change from one MH band to another. The crystal of one or more band may 
have good output level but be off frequency. Rather than speed big bucks trying 
to get a bunch of crystals all with about the same error its just cheaper to 
live with the various errors and use the zero adjust when needed. Most days 
the receiver error and use are well within bounds and lots of zero adjusting is 
not needed.

I hope this helps with this one problem.
Keep working on the others.

If you need some knobs to get your front panel back in shape, ask here on the 
reflector for what you need. You will get someone on one mail offering you 
some parts. The R390 and R390/A knobs are interchangeable. Down load the R390 TM 
off the reflector and you will see what size knobs go where.

http://www.r-390a.net/

If you have a knob with a stripped set screw hole it can be drilled and 
tapped to a larger size and still used. The Large MC and KC knobs have a clamp 
inside them. The clamps break. New clamps can be located here buy asking for them 
if you need them.

You can swap the spline bolts around in the various gear and knob clamps to 
get the spline bolts in where you need them often (IF deck and Large knob 
clamps) you can then put a 4-40 bolt with a slot head in some where else that you 
may never need to adjust again. Once you get the mechanical alignment set, it 
may never need resetting unless you do some disassembly work for a repair.

Roger AI4NI

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