[R-390] R-390A trouble

[Bill Smith]

Sounds like one of the stages controlled by the AGC circuitry is oscillating
for some reason.  High probability of a leaky cap, or off-value resistor.
AGC drops, stage oscillates, AGC is boosted, stage stops oscillating then
AGC drops.. in a cycle.  You might try manually controlling the AGC voltage
and look for the (unstable) stage that is charging the AGC circuit.

Bill

----- Original Message -----
From: "Jim Temple" <jetemp@insightbb.com>
To: <r-390@mailman.qth.net>
Sent: Wednesday, March 27, 2002 2:42 PM
Subject: [R-390] R-390A trouble


> Hi Roger and list,
>
> OK, I want to fix this receiver.  Here goes.
>
> 1.  R-390A bought as a "massacre" yellow line from Fair Radio.
> 2.  After cleaning, and replacing many of the "problem" caps (listed on
many
> of the resident web sites), I corrected a below 8mhz problem, by finding
> that the ground lug under T-207 was loose and insulated from ground by a
> shellac layer.
> 3.  The unit, at first alignment, aligned well.
> 4.  At some point, within a couple of hours of operation, the receiver
> developed a screeching/motorboat putt putt sound.
>
> Symptoms:
>
> 1.  On bands 00,01,02, and 03, the screeching/motorboat sound is not
> present.
> 2.  Above band 03, the motorboat sound will vary in amplitude and putt,
putt
> frequency with adjustment of the antenna trim control, and becoming more
> intense as band increases.
> 3.  The carrier level meter indication increases as the amplitude
increases,
> the strongest coinciding with the antenna trim peak prior to the problem
> developing.
> 4.  The AGC control will change the frequency of the putt,putt, depending
on
> the position of the control.  Fast=fast.  Slow=slow, or right on the edge
of
> putt,putting.  Medium=medium frequency.
> 5.  The AGC voltage measures about 8-9 volts during the motorboating.
> 6.  The screeching/motorboat sound disappears with removal of V201/'6DC6.
> 7.  I replaced the antenna trim assembly with a spare from a spare RF
deck,
> with no change.
> 7.  The ohm reading of the antenna trim vertical shaft is 1.5meg, and
> doesn't vary with rotation of the control.
> 8.  With the RF deck removed the antenna trim wires measure a smooth
> increase and decrease of the variable caps within the enclosure.
>
> I have inspected and examined the bottom components of the RF deck several
> times and can find no shorts or broken wires.
> I am positive the RF deck timing is correct.  I have triple checked the
> timing and am positive it is correct.  The deck did work fine for a couple
> of hours.
>
> My troubleshooting skills are lacking, so sometimes I do not approach a
> problem in a logical fassion.
>
> My approach will be to thouroughly examine the RF deck components.
Measure
> the values of components I reasonably can.  I thought the voltages in the
> Y2K manual were measured with the tube in place, but I am unsure at this
> point.
>
> There is clearly a great deal of knowledge and expertise on this list, so
I
> hope my lack of troubleshooting skills will not get in the way of a fix to
> this receiver.  I may need a little more "hand holding", detailed
coaching,
> than the average owner.
>
> Thanks for listening.  I hope I have given enough detail to get me started
> on the right road.
>
> Sincerely,
>
> Jim
> 73, KF4ICZ
>
> ----- Original Message -----
> From: "Roger L Ruszkowski" <rlruszkowski@Raytheon.com>
> To: <r-390@mailman.qth.net>
> Sent: Wednesday, March 27, 2002 12:01 PM
> Subject: Re: [R-390] Fw: Alignment help.more
>
>
> >
> > Jim,
> >
> > What are you doing to an R-390/A.
> snip....
> > List your problems here and get some specific help.
> > Quit trying to solve and reinvent it all by your self.
> > It is more fun that way. I do agree.
> snip....
> > What is your real objective?
> > Do you want some tube extenders, or do you want to fix a receiver?
> >
> > Roger KC6TRU San Diego.
> >
>
>
>
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