[R-390] Dead R390A Need HELP

[Miles B. Anderson]

The very first thing to do is to be certain that the jumpers (RF gain
control to ground 1 to 2, AGC to normal 3 to 4, diode detector output to
audio input 14 to 15) have been installed on the back panel terminal boards.
Any one of these will kill the set dead.

The very second thing is to make sure that all of the interconnect plugs
(both the mini-BNC RF cables and the power plugs) between the modules are
properly connected and fully seated. A loose or disconnected plug from the
VFO to the RF deck will produce no signal. Don't forget to check the cabling
to the antenna relay.

One more quick fix -- be sure the Noise Limiter is set to OFF. When it
works, the Noise Limiter pretty effective at killing the audio at anything
above "2" or "3" on the dial. When the pot wears out it's even more
effective. The OFF setting bypasses everything.

If you don't have test equipment, there are a couple of quick checks you can
perform:

(1) Turn the radio on, let it warm up and leave it on for all of these
tests.

(2) Det the FUNCTION switch to MGC and both the RF and Audio gain controls
wide open:

(2) Crank the IF gain pot on top of the IF subchassis wide open.

(A) You can hear scratchiness when diddling the Audio Gain control. That's
the first test,and the radio passes.

(B) Pull V602 out of the socket on the IF chassis. You should hear a "pop"
on audio. If not, the problem is somewhere between V602 and the Audio Gain
control (2nd or 3rd IF amplifiers, detector or audio preamplifier). If OK,
reinsert the tube.

(C) Pull V601. You should hear the same thing, only louder. If not, the
problem is the 1st IF stage, the BANDWIDTH switch, or the mechanical filter.
If OK, the IF subchassis and audio subchassis are probably good enough to
hear something.

(D) Rotate the MEGACYCLE control to some setting above 7 MC -- say 8 MC.
Then slowly rotate the control between any two adjacent stops (say 8 MC and
9 MC). You should hear a "pop" and a change in the noise level when the
switch goes out of detent. If not, the problem is: the 1st or 2nd mixer or
the crystal oscillator.

Last: Remember the doctor's adage; "When you hear hoofbeats, think horses,
not zebras." That is, look for the most common faults: (1) a bad tube or the
wrong tube; (2) a disconnected plug -- before looking for something exotic.

Miles Anderson, K2CBY
16 Round Pond Lane
Sag Harbor, NY 11963
k2cby at arrl.net

-----Original Message-----
From: r-390-bounces at mailman.qth.net
[mailto:r-390-bounces at mailman.qth.net]On Behalf Of Thomas Guest
Sent: Thursday, September 22, 2005 6:40 AM
To: r-390 at mailman.qth.net
Subject: [R-390] Dead R390A Need HELP


Hi everyone,

I am new to the R-390A but do antique radios. I may have bitten off more
than I can chew at the moment but I hope that will change.

I picked up this set from Fair Radio (used repairable) and powered it up and
get almost nothing.

I have replaced the killer cap in the IF, the 8 ufd audio section cap, and
the electrolytic tests good at full rated voltages. Fuses are good. I have a
short antenna 20' hooked up to the balanced input with the other half of the
connector grounded to the chassis. The ballast tube is good. The brown
beauty caps in the set have NOT been replaced! I see B+ of 285Vdc at the
back panel fuse.

I have a Hallicrafters R-42 speaker (600 ohm input) tied to the set and get
only a faint scratching noise from turning the volume control.
No signals across the board on this set. The carrier meter deflects about ½
way (my meters are not the factory ones) and I get no deflection on the line
meter.

Problems that I did find was the VFO was not connected to the front panel
knob, & the rear terminal strip was loose and could have been shorting the
RF gain jumpers to the chassis. After fixing these issues still have the
same results.

Any ideas on where to look next?

Or is there a way I could inject signals into the set to prove out a section
at a time?

Thanks in advance.
Tom Guest





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