[R-390] Cleaning Gearbox Assembly

[Jim M.]

I would soak only the gear assembly in kerosene, but carefully.  I would not
soak any of the electronics  - just my preference. I believe the tube
sockets and switch wafers can absorb chemicals and oils, making them
slightly conductive - in high impedance tube circuits, this may cause
anomalies such as poor AGC, and can destroy trimmer caps.  Getting oil into
the phenolic insulator on the antenna trim shaft can also cause AGC problems
or other strange things.  Also when coil forms absorb liquids and oils, they
can expand - this may be what causes some coil slugs to stick.  I do not
agree with extreme measures such as dishwashers, although it might work for
some.  Short of disassembling the gear train (which is the best method I
believe), an acceptable way for me is to place the RF assembly on the edge
of a bench with a pan under the gear assembly, and squirt kerosene down into
the gears to wash them out.  You will see the gunk collect in the pan.  Then
some compressed air, then more kerosene...then some light weight "Marvel
Mystery Oil" (I think that's the name).   Big Bath spray also works well
afterward to remove any oil residue that may have sneaked into the
electronics compartments.  Q-tips and elbow grease work well in the
electronics compartments.   Just my 2 cents worth.

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of ToddRoberts2001 at aol.com
Sent: Sunday, November 04, 2007 8:05 AM
To: r-390 at mailman.qth.net
Subject: [R-390] Cleaning Gearbox Assembly

I found the Kilocycle Change control disc and split gears I needed for the 
play in the tuning mechanism, but before I put it in, is there any way of 
cleaning the gunk off the whole gear assembly in a 390 without taking it all

apart?

Bob
KB1OKL
 
 
Hi Bob,
When you say "without taking it all apart" do you mean the gearbox assembly 
itself or taking it out of the radio?  If you can take the whole gearbox 
assembly out of the radio in one piece I have had good luck soaking the
whole thing 
in a tub of kerosene for a few days, swishing around the gears and cams with
a 
paintbrush from time to time and turning the bandswitch a few times. After 
soaking a few days the bottom of the tub will be covered with dirt and crud
and 
the whole gear assembly will look like new. 
 
One thing you do have to watch out for with the kerosene is to remove the RF

transformers first. The kerosene seems to get into the rubber washers in the

small ceramic trimmer caps and swells up the rubber - I found that out the
hard 
way. Keep anything with ceramic trimmers out of kerosene.
 
After soaking a few days let the unit air-dry for a few days. All this
should 
be done outdoors if possible covered or in a ventilated workshop or garage.
I 
have sped up the drying process by placing the unit directly in front of a 
dehumidifier and let it blow warm, dry air on the unit. When it is dry all
the 
bearings or sleeves will be dry also. I have had good luck spraying
everything 
with a light coat of penetrating oil then manually lightly re-oiling all the

gears, bearings and sliding parts. Spraying the RF switch parts with some 
de-oxit is a good idea also before reassembly into the radio.
 
73 Todd WD4NGG



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