[R-390] Parts Needed, new R-390A owner & questions...

[Paul Anderson]

Hi Steve, welcome to the group!

On Tue, Sep 8, 2009 at 2:03 AM, Steve Kent<steve.kent at att.net> wrote:
> Hello All:
>
>
>
> I wanted to be very cautious before powering it on, knowing that there
> are some caps with bad reputations.  So I set out to give it a good once
> over and take a close look around.  It's a good thing I did.  Upon
> removing the IF deck I discovered a blackened area with L505 fried and
> R508 blown up. C553 tests OK but I am replacing it; I expected it to be
> shorted.

C553 doesn't short any more often than the others, it is just that if
it does, it can fry your filters real quick, so replacing it is a good
idea.

So you need to find out why the coil fried - there is probably a
shorted cap nearby in the circuit - test everything with a VOM,
resistors and caps both (resistors simply due to the heat and stress
in the immediate vicinity).

The other problem areas are the the big electrolytic audio caps, which
will often hum or if they short, fry the audio transformers or they
can leak, which makes a mess.  The shorting problem seems like common
than the other two.

There is a small cap under the audio deck in the middle of the little
circuit board that often goes bad and makes a mess - it is worth
replacing that one too.

As to the other caps, opinions vary, but one consensus is that
wholesale replacement of the BBOD (black beauties of death) is
worthwhile.  It does depend on the age of the deck, past use, your
time and how you value it, and so on.  I replaced a bunch in I think
two R-390A IF decks, and that was fine, but maybe in the future, I'd
just replace C553, and leave it at that - test the deck and see how
well it works before redoing it.

Other R-39X radios (R-389, R-390, R-391, R-392) seem to have slightly
better quality caps, but they also tend to be older (early to mid 50's
for the 389/390/391).  Later R-390A decks have much newer caps, and
perhaps better manufacturing, but they are still paper caps,
nonetheless.

I can't think of any other serious problems to watch out for, other
than the usual common sense stuff - check resistors, they drift high
often, due to heat (mind you also due to resoldering capacitors, so
this is  another incentive NOT to wholesale recap a deck).  I've seen
some crack just due to age or heat, too.

Paul

>
> Best Regards & 73,
> Steve - KW5CQ
> Houston, TX
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