[R-390] This may be of help to someone
Roger Ruszkowski
flowertime01 at wmconnect.com
Fri Feb 27 11:29:35 EST 2015
Bill,
Thank you for taking the effort to repair this receiver.
Nice to hear that another receiver is operational again.
Roger Ruszkowski AI4NI
-----Original Message-----
From: Steve Toth via R-390 <r-390 at mailman.qth.net>
To: Bill Abate <wabate at verizon.net>; R-390 <R-390 at mailman.qth.net>
Sent: Thu, Feb 26, 2015 3:02 pm
Subject: Re: [R-390] This may be of help to someone
BillGood job at logically overcoming a compound problem - especially the extra
long RF assembly mounting screw piercing the wiring harness! - Steve
"Always
look for a positive solution then Improvise, Adapt, and Overcome"
A veteran -
whether active duty, retired, National Guard or Reserve - is someone who, at one
point in his or her life, wrote a blankcheck made payable to "The United States
of America" for an amount of "up to and including my life."
From: Bill
Abate <wabate at verizon.net>
To: R-390 <R-390 at mailman.qth.net>
Sent: Thursday,
February 26, 2015 10:56 AM
Subject: [R-390] This may be of help to someone
After repairing and aligning (I dislike the word 'restoration') four
other
R-390A's I thought another would be no biggie. I bought my fifth
a few years
ago at a great price and then put it on the shelf for a
future project after
doing some cleaning and degreasing. Recently I ran
out of 'round to's and
remembered the 390A. After a power up with no
smoke I put in the missing tubes
and connected a speaker. Zipo!
Nothing! A close inspection showed that the
megacycle knob did not turn
all the related gears. A gear clamp was broken.
Darn! Now I had to
mess with the gear train to get at that clamp. Even worse,
a magnifying
glass and flashlight showed six more broken clamps!
After hours
of machine work I fabricated some replacement clamps. I
replaced the clamps
and reassembled the gear train. Darn, the gears
were still slipping. Turns
out the gear (#48) was slipping but the
clamp was tight. Removed the gear and
found the hub to gear connection
was a cold solder joint. Yes, its called out
in the military manual as
a soldered gear (its not tin/lead solder). Did not
expect that! I was
worried about the heat damaging the gear if I tried to
resolder it since
it is tempered steel but I could not come up with a better
idea. I dug
out my low temperature silver solder and oxyacetylene torch. The
gear
repair turned out well. I did not give it a complete fillet as original
since I wanted to keep the heating time to a minimum. The gear did warp
slightly despite being tacked in just two places but it still was
usable.
Evidently the gorilla who worked on the gear train before me
kept tightening
the clamps until they broke when he could not stop the
gears from slipping.
Brawn instead of brains!
Next problem was to synchronize the gear train. When
the broken clamps
allowed some of the gears to slip on their shafts it became a
giant
Rubik's Cube. I never felt the need to disassemble a gear train before
so this was all new to me. I set the cams where they belonged at 7 +000
but
then found out the bandswitch was not synchronized. I found the
section on
synchronizing the 6 position RF bandswitch that showed you
get a 56K resistance
between two points (page 110 of TM 11-5820-358-35)
when at 7 +000 setting. So
I loosened the gear on the band switch shaft
and rotated the switch shaft until
I got the 56K reading and then an
infinite reading when switched to 8 MHZ. You
must satisfy both
requirements. When that got satisfied I reassembled the rig
but I still
could not get the radio to align. Turns out there is more than one
shaft position that satisfies the test. After studying the schematic it
turns
out the easiest way to synchronize the band switch is to look at
the rear wafer
and verify B+ to the 17 MHz oscillator when in the 00 to
07 positions. Finally
got it right. After dropping the front panel and
removing the RF subchassis
more times than I care to admit, I found I
still could not align the radio. I
neglected to align the switch gear
assembly (#87). I could not find explicit
alignment instructions in the
manual other than to use figure 68. I carefully
positioned the bottom
cogs with the vertical centerline of the gear and finally
got the radio
to align properly! It took me over a week to diagnose and fix
these
problems. Yeah, I'm slow.
Thought I was done at this point but the
audio did not sound right. It
passed the tests for the AF module but it just
wasn't right. Playing
around with various settings I discovered that turning
off the noise
limiter made the audio louder and better. HUH? Found no B+
getting to
the noise limiter tube plates. Pulled the AF module and the
switched
RF-IF B+ was there but the line to the noise limiter switch was
grounded. Could not find anything bad in the module so I disconnected
the
multiconnector plug and the ground disappeared. So it was in the
wiring
harness. Figured the switch on the noise limiter was bad. But
it was fine.
YUK! How do I find a short in the fully laced harness?
Well dumb luck
prevailed. When I moved the harness in a certain
location, the ground
disappeared. Turns out it was right next to the
PTO. Now this might help
someone. Somebody put an extra long screw
through the frame that holds the RF
assembly in place at that location.
The harness is on the other side of that
screw. Sure enough the screw
pierced the wire insulation at that point and
shorted that wire to
ground! Replaced the screw with a shorter one and added
some electrical
tape and all is well.
Sorry this got to be so long but it
might help someone else. I could
not find something similar on synchronization
but if this has been
covered before, my apologies.
Bill,
K3PGB
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