[R-390] Saturday's Line & Local Report

[Craig Heaton]

Hello Bob,

With the ends of the wiring already soldered, moving the wire harness isn't
going to happen. It could in the future cause other problems from tugg'en &
pull'en. Last night I was able to get a small mirror under the harness and
check for damage, couldn't see any. Just in case a layer of tape was added
between the harness and studs. This one isn't going to be bouncing around in
the back of a duce & a half. 

After bringing the boombox home I was pleased with its physical condition.
Very clean, no corrosion, no signs of being mounted in a rack, original
tubes. The only mod found so far; the socket for the ballast tube was
rewired for a 12BY7. Now the socket is wired for the proper tube, pins 2 & 7
have a jumper, 12BA6's in place of the two 6BA6's. 

I'm sure one of the past owners pondered the audio. The 5K local gain pot
wasn't put there by the Wizard of Oz. The speaker that was included had two
(2) impedance transformers attached. One of each end of the speaker wire.
Beats me?

Tisha,

What I can't remember doing is putting both IF & AF modules from the
Motorola into the Amelco, "at the same time".........................So
looking just at the physical condition, what did the manufacturers of
R-390/A's do with some of the rejects? Some how, did I get a R-390/A with
several modules with problems that no one was going to fix? As is, the
boombox has good sensitivity, no distortion on strong stations using AGC. I
don't have the option of placing it on the bench of another tech and I
always question the test equipment and "me". This is the reason for only
spending a week or so with the boombox. Another year, a fresh look might see
the problem(s).  

Going to take a hard look at the Amelco IF today.

Regards,
Craig

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of rbethman
Sent: Sunday, January 05, 2014 8:34 AM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] Saturday's Line & Local Report

Craig et al,

Your previous comments regarding the jumper being discovered begs the
following mental/physical exercise.

The wiring harness itself.  You have noted the "positioning of the wiring
harness" in two places sitting on top of mounting studs.

I might suggest looking at possible fraying of the harness, and a point
where it "may" be causing two or more conductors to be bare and touching
each other and/or the chassis itself.

I might say that the harness is suspect, as you have found the jumper(s) and
components touching a jumper.

In my mind, this gives the impression that it has been fiddled with "after"
production.

Does anyone else get this from all the posts?

It is just a bit suspicious in my mind.  Even those from St. J's don't have
those type of issues.

Bob - N0DGN

On 1/5/2014 10:56 AM, Craig Heaton wrote:
> Good Morning Charles et All,
>
> Sometime today the IF output of both receivers are going to be checked.
> Money says I'll order some new caps and see what happens. Every year 
> for the last couple of years I've spent a week or so going thru the 
> Amelco searching for the loud audio cause. If it were no audio, could 
> be easier to find. Loud audio, just turn down the RF gain a tweak. If 
> the caps don't fix it, the boombox goes back to its operating station for
another year.
>
> The AF section was checked last night again; wiring good, resistors 
> good, all but two caps have been replaced (C612,C601) C601 looks like 
> a Vitamin Q,
> C612 is a silver mica. J619 & J620; terminal resistance checked per Y2K.
>
> I'm tired of swapping modules. Where I can pick a point and check 
> voltages, watch the O'scope, etc; much easier.
>
> Several times the boombox has been mentioned here on the R-390 e-mail 
> reflector. C603 is the leading cause in replies. At this point, caps 
> are like tubes, check them in circuit. The values of all three are 
> good to go, leakage is very low according to the TO-6A.  If it should 
> bypass all audio to ground, we have a suspect.
>
> This week hasn't been a total loss. The jumper touching that resistor 
> wasn't found before. I might add the positioning of the wiring harness 
> in the Amelco lacks a little. There are two spots where the harness 
> sits on mounting studs. Have to wonder how that got past a military
inspection.
>
> Regards,
> Craig
>

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