[R-390] Damge Control (Was HP410B Intermittents)

[Don Reaves]

Mike, 
I once claimed salvage rights to a NCR modem that some marketing company
abandoned in our office building.  Being a late 50's or early 60's
technology, rated for 300 baud, it was in a rather large heavy steel box,
about 36 inches tall, 24 inches wide, 18 inches deep.  It was full of wiring
harnesses, circuit boards, heavy duty power supplies and connectors.  I
loaded it on my 12 foot flat bed utility trailer towed by my truck, and
decided the box was so heavy I did not need to tie it down for the trip
home.  Well, about the third bump in the street during rush hour traffic the
modem decided to jump off the trailer, and annoy drivers behind me.
Fortunately, disaster was avoided, there were no liability claims as I was
able to hastily retreat and scoop it up before the gestapo arrived.  It is
fun to think about that big hunk of smashed up gear lying in the righthand
traffic lane, and hundreds of cars having to avoid it before I could
retrieve it.  Who knew a 300 baud modem could impede auto traffic so well?

So it got a hefty theraputic thump, but it did not work very well after
that.  

All the above to preview that I received an R-389 receiver in by UPS and the
poor thing is pretty well defeated by shipping damage.  Who has had success
with fixing bent up R-390 type chassis frames?  Barry Hauser had some tips,
which I have filed somewhere for reference but it escapes me for the moment.
Is there a ready reference for sheet metal aluminum massaging?

Don


 

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net 
> [mailto:r-390-bounces at mailman.qth.net] On Behalf Of mikea
> Sent: Tuesday, May 26, 2009 08:27
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] HP410B Intermittent(s)
> 
> On Mon, May 25, 2009 at 12:13:33PM -0500, Don Reaves wrote:
> > 
> > > get go.  Removing the old gucky solder then liquid flux and heat 
> > > seemed to give a ok joint.  It was surprising to see that kind of 
> > > problem inside of an HP instrument.
> > > 
> > 
> > Not unheard of.  I once found the problem with an HP-200R 
> with intermittent
> > output to be that a b+ line leading from the power 
> transformer had never
> > seen a hint of solder.  The wire was wrapped on the 
> transformer solder lug,
> > and it probably worked OK for a few years, then slowly oxidized.  
> > 
> > A slight variation of the Stockdale technique to restore 
> operation of a
> > BC-375 worked on the HP-200, before the proper repair was 
> implemented.
> > 
> > http://www.youtube.com/watch?v=TBXmVqcAP6M  (at about 2:30 
> in this clip)
> 
> I'd totally forgot that part of the movie. Now I have to get 
> coffee out
> of the keyboard on the other computer. And send my pants to the
> cleaners. 
> 
> Folks here may be interested to know that the USAF (and, presumably,
> other services) had a 300-Baud modem with mechanical 
> resonators, back in
> the late 1960s. It had glowbugs, too, as well as a 
> regrettable habit of
> ceasing to produce tones. When it stopped whistling, then it 
> was time to
> whack it _HARD_ on the lower right corner of the front panel 
> to restart
> the resonators with a mechanical shock.
> 
> We replaced that critter, but nowhere near soon enough for me, with a
> Rixon SeBit 24 that was about the size of a paperback book -- lots
> smaller than the 6 rack units that modem ate, and lots cooler, too.
> 
> -- 
> Mike Andrews, W5EGO
> mikea at mikea.ath.cx
> Tired old sysadmin 
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