[R-390] R-390 Digest, Vol 112, Issue 14

[frank hughes]

Hi,
Thanks for all the tips and advice, I feel much more confident in getting
R390 #2 working now!

I have a solid state kit from Tom, N3LLL to replace the 6082's and cool
things down, but am waiting until
the bugs are out of this R390 before doing the mod.

Thanks for clearing up which modules I can unplug for testing, and which
should stay in place to retain B+ regulation.
I read Dave Medley's tips about it, but the TM describes removing modules
until the short is isolated, so I was confused about what to do.

I thought about using the good R390 to swap modules into for fault
isolation, but I don't know enough about these radios to be sure that
putting a
 bad module in a good radio might damage something in the good R390.
Discretion being the better part of valor, I would rather learn how to
isolate the trouble in situ.

3/8A fuse wiring - WOW, I would have never have caught that change, now I
know what to look for.
I have a pile'o R390 power transformer assys. that I have been swapping in
and out, not knowing that they might be
a mismatch for the way this R390 chassis is wired.

I'm looking forward to going back to the office Monday so I can try all
these tips and techniques!

I have the "project" R390 and the HP 410C from Ashley, W7DUZ, plus various
other ancient HP test equipment
set up in a discrete corner, disguised to look like part of the rest of the
CISCO network gear.

Lunchtime and the occasional break lets me fool w/ the R390.

The young people in the office think it is a CISCO router.

 "What are those little glass things?"
 "Air filters"

73
Frank
KJ4OLL


On Sun, Aug 11, 2013 at 12:00 PM, <r-390-request at mailman.qth.net> wrote:

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> Today's Topics:
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>    1. R390 troubleshooting - I'm stuck, 3/8A fuse pops (frank hughes)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 11 Aug 2013 09:58:46 -0400
> From: frank hughes <fsh396ss at gmail.com>
> To: r-390 at mailman.qth.net
> Subject: [R-390] R390 troubleshooting - I'm stuck, 3/8A fuse pops
> Message-ID:
>         <CAKLfjC=9+5xqmhQMbAmxvjDJL1HO1=
> 9wZHoqBVHd3HAOuz1MzQ at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
> I bought an R-390 from a "yard sale" parking lot table at the Orlando
> Hamfest.
> It looked very complete and possibly not previously mangled excessively.
>
> The seller said it was "Only used on Sundays by a little old lady...."
>
> Anyway, when I got it home and was able to remove some of the decks for
> inspection, discovered the IF assy. had been tinkered with, and was
> non-functional.
>
> I put in another spare R390 IF assy., brought the unit up on w/ Variac, and
> detected the delicate odor of carbon comps smoking.
> Some of the resistors in the power supply were cracked.
> After prolonged inhalation of these fumes, I found myself longing to vote
> for Democrats..very strange.
>
> Subsequently replaced all of the 47 ohm cathode balancing resistors in the
> audio module (the B+ regulator section) and the power supply (rectifier
> cathodes), with wirewounds.
>
> Replaced the copper oxide relay selenium rectifier CR801 with diodes.
> Ran all the tubes through a TV-10, replaced the defective ones.
>
> The unit still pops the 3/8 A fuse.
>
> B+ is going way over 180V.
>
> Went to TM11-5820-357-35 and started the step-by-step troubleshooting
> procedure for 3/8A fuse opening.
> - C607, C101 are not shorted.
> - measured from the 3/8 fuse to ground, = 148k ohms through V605, V606.
> - Chassis ground to B+ jack shows 19k ohms, function switch=OFF
> - Chassis ground to B+ jack shows 9.4k ohms, function switch= AGC, MGC. CAL
> - Chassis ground to B+ jack shows 8.5k ohms, function switch= SQUELCH
> So all this checks out.
>
> The next section has me perplexed.
> 46. Checking Filament and B+ Circuits for Shorts;
> d. Locating a Short Circuit. If the tests out-lined in "c" above indicate
> that there is a short circuit in the receiver, determine in which
> subchassis it is located as follows:has me perplexed.
>
> All the tests in "c" passed, so if there is no short circuit, why is the
> 3/8 fuse opening?
>
> I am not too proficient at test & troubleshooting, but really love these
> radios, and want to learn how to do these things, so any advice for other
> things I should try would be appreciated!
>
> I have another R390 (pristine), obtained from KW4DH, used for SSB.
> The audio quality is amazing. (diode load to a KRK ROKIT 5" Studio Monitor)
>
> My goal is to use this second R390 w/ the 32V-2 for AM nets, if it can be
> saved!
>
> Thanks and 73
> Frank
> KJ4OLL
>
>
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> End of R-390 Digest, Vol 112, Issue 14
> **************************************
>