[R-390] R390A- Intermittent sensitivity variation

[Flowertime01 at wmconnect.com]

Eric,

Try the R390.net page and Wi's pearls of wisdom
Look for stuff on the RF band switch adjustment.

Jump in and get your reciever fixed.
It is just a slow screw job.
It will take about 8 hours to just pull the receiver apart, do some 
cleaning, do some mechanical adjusting and get it all back to gether. 

You will need the spline wrench, and  long #1 Philips screw driver to get 
to the green screws along the top back of the RF deck.

You will want to do a complete RF deck alignment once you get the 
mechanical work completed. 

A good brand of electrical contact cleaner and cotton swabs.

More detail than you ever wanted.

Use the Y2K manual to get the Rf deck out of the receiver.
Turn the RF deck up on it top.
You should be able to run the MHZ shaft through it range without the RF 
slug studs sticking out of the top of the deck and jacking the deck up off the 
bench.
If not set the deck on what ever to make a suitable working arrangement.
As you dial the MHZ shaft through its range you will see the octave gear, 
change the RF band switch at the needed points.
[.555 - .999, 1,000 - 1.999, 2.000 - 3.999, 4.000 - 7.999, 8.000 - 15.999, 
16.000 - 31.999]
Do not worry about the KHZ shaft.
Do check the cams and the mechanical alignment before going on.

see end H. Mechanical Alignment

As you rotate the MHZ shaft and the band switch changes,
look at the wipers and the contacts. 
Check all six sections and all six positions.
You are likely looking for a discolored contact on the last contact (16- 32 
position) that is just oxidized and needs some cleaning.

You may want to clean all the switch contacts
And change out the big brown caps under the RF deck if you have any.
As long as you are this far in, clean and lube the whole RF gear train.

As you rotate the MHZ shaft through it range and the octave gear switches 
the RF band switch through its six contacts, look at each wafer section and 
each contact as the wiper makes with the contact. Look at the mechanical 
mating as the octave gear switches the RF band switch through its six contacts 
both working up the bands and down the bands. Due to mechanical play the 
contact will not be equal going both ways.

A very small adjustment will get you better contact.

Over time these switches have been not adjusted for optimum wiper to 
contact mating.
Thus a barely making contact and wiper will have its corner burn off or 
oxidized away. So it becomes a matter of just doing your best eye ball and 
selecting an adjustment that gets the best contact at all the right places at 
all the right time. This is one of those simultaneous equations that needs to 
be solved for every combination.

The actual adjustment is to lossen the clamp on the RF switch shaft gear 
and just nudging the shaft one way or the other counter clock or clock wise a 
very small RCH or less. Then tighten the clamp and repeat the eye ball 
inspection.

The TM implies you can do this without looking under the deck.
That author is no longer living.
That author did not understand what he was writing about (mechanical 
challenged).
That author had no real experience or would never have written what he did 
write.
Doing it like the TM says it what gets the switch contact area reduced.

In an extreme case you may need to actually replace a switch section 
because it is beyond adjustment. As your receiver works, there is some adjustment 
point that will return your receiver to good operation and solve the drop 
out problem you are experiencing.

Do let us all know what you find and how it turns out.

Roger Ruszkowski  33C4H 68-75 AI4NI

H. Mechanical Alignment
___ 01 Set Oven switch to OFF
___ 02 Loosen the dial lock, check the knob and lock operation
___ 03 Check the zero adjust knob adjustment operation
___ 03 Set the zero adjust to center
___ 04 Check the over run and under run on the KHz knob (10 turn stop)
___ 05 Adjust the KHz counter as needed (greater than 25 -963 , -972 )
___ 06 Check the over run and under run on the MHz knob (10 turn stop)
___ 07 Adjust the MHz counter as needed
___ 08 Set the R390A to 7+000 Set the R390 to 2.000
___ 09 Check the cam alignment starting with the 8-16 MHz Cam
___ 10 A If the 8-16 MHz Cam need adjusting then loosen the following
___ 10 B Release the clamp for 2-4 the slug rack should fall
___ 10 C Release the clamp for 4-8 the slug rack should fall
___ 10 D Release the clamp for 16-32 the slug rack should fall
___ 10 E The 8-16 slug rack should also fall
___ 11 Hold the 8-16 and 16-32 cam in place
___ 12 Tighten the 16-32 MHz Cam clamp
___ 13 Hold the 4-8 cam in place
___ 14 Tighten the 4-8 MHz Cam clamp
___ 15 Hold the 2-4 cam in place
___ 16 Tighten the 2-4 MHz Cam clamp
___ 17 Adjust the 1-2 MHz Cam if needed
___ 18 Adjust the . 5-1 MHz Cam if needed
___ 19 Adjust the 1st Variable IF Cam if needed
___ 20 Adjust the 2nd Variable IF Cam if needed
___ 21 Adjust the VFO if needed

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