[R-390] R390A- no sigs-4 to 8mc

[David Wise]

It's the RF deck; probably its bandswitch or one of the 4-8mc RF transformers.
Those are the only circuits that operate by octaves.

It can't be a slipping 4-8 gear; that would misalign everything mechanically
downstream, i.e. 8-16 and 16-32 PLUS the 7-25 variable IF which brings you
0_500 to 7+000; in short, everything.

Crystal problems would knock out two or three seemingly unrelated 1mc bands, or
(in the case of the 17mc oscillator) 0_500 to 7+000.

Look for a dropped slug, a bad winding, or failure to "make" in the bandswitch, which
can be picky.  Ohm it out as Tisha suggests.  Do this first so flexure doesn't miraculously
cure it and leave you without a diagnosis.  Since it's some work to R&R the RF deck, use
the opportunity to replace any molded oil/paper caps lurking there, and check for
out of tolerance carbon comp resistors.

HTH,
Dave Wise

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Tisha Hayes
Sent: Tuesday, February 03, 2009 9:08 AM
To: r-390 at mailman.qth.net
Subject: [R-390] R390A- no sigs-4 to 8mc


Two other areas that can cause a dead band;

Look at the rotary switches under the RF deck and under the oscillator deck. I had a very slight mechanical misalignment and severe oxidation that caused the 2-4 MHz bands to be dead.

The two problems were not obvious on a visual inspection. I had to ohm though the switches from the cans on the RF deck and had to have the oscillator deck powered up and checked the output on the coaxial cable to catch the oscillator switch problem.


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