[R-390] Re: Depot Dawg / Capacitor leakage test

Wed, 28 Aug 2002 17:02:47 -0400

Philip,

In his response to your concerns about capacitors Bob Camp mentioned a  
setup for leakage testing using power supply, current limiting resistor, and 
microammeter.  Chances are you already have the meter with the current 
limiting resistor built in.  It is your DVM or VTVM (Zin=11 meg). Use the 
meter in the dc voltage mode.  The leakage current can be calculated as 
Vmeter/10 meg.  The good thing about this test is that it is even more 
sensitive than the one Bob mentioned.

For a detailed description (and debate on all facets of R-390x capacitors) 
goto R-390a.net.  Select References>Pearls of Wisdom>Recapping. On pages 99 
and 100 there it will be, along with much other fascinating reading.

Drew

>Message: 15
>From: "Bob Camp" <[email protected]>
>To: "Philip B Atchley" <[email protected]>
>Cc: <[email protected]>
>Subject: Re: [R-390] No "Depot Dawg"
>Date: Tue, 27 Aug 2002 02:49:43 -0400
>
>Hi,
>
>I guess this is what makes it a hobby. I would vote with you - a unit that
>is "all original" is slightly cooler than one with mixed modules. That's 
>not
>to say better or more functional, just cooler. Needless to say this issue
>has come up before. Of course with very few exceptions (say 10 radios) 
>there
>is no way to *ever* prove that a radio is original so you never really 
>know.
>
>The metal/glass package capacitors are better than the black plastic 
>package
>ones. The yellow plastic wrapped ones are Mylar (or similar) with a plastic
>insulation. About the only disadvantage to the yellow ones is that when you
>hit them with a soldering iron they melt.
>
>The thing that makes the black or brown caps a problem is that the
>insulation is paper (or paper with mica in it). The stuff soaks up humidity
>and then they get leaky. The whole process really gets going when the case
>splits open.
>
>Leaky capacitors aren't all that hard to check. You can use a fairly simple
>setup. Get as sensitive a meter dc meter as you can find. A good old Weston
>or Simpson analog meter works well. If you can find something in the 10 or
>20 ua range that should do. Then set up about a 100 volt power supply.
>Stacking two 48 volt units is one approach. One microampere at 100 volts
>works out to 100 meg ohms. A 10 meg ohm series resistor will keep you from
>blowing out the meter. New from the old box plastic capacitors will all 
>read
>"no deflection" on the meter. Every black or brown body cap I have ever
>checked reads at least a couple of micro amps.
>
>If you have a doubt about a type of capacitor find one that you can pull 
>one
>end on. Hook up the tester and see what it reads. If it's ok then solder
>that end back in. On the truly bad stuff you won't be able to find one good
>one .....
>
>Both the green and brown switch wafers will soak up de-oxit. The brown ones
>swell up a bit more, but they both retain the stuff. In either case it's
>probably not a  good thing, but nether are dirty contacts.
>
>One thing you might do while you have the RF deck out of the radio - meg 
>out
>the AGC line and see what it reads. I have never tried it but each time I
>put a deck back in I kick my self for not thinking of it. I have no idea
>what it should read, but the schematic should be fairly easy to follow.
>
>     Enjoy!
>
>         Bob Camp
>         KB8TQ
>
>
>
>----- Original Message -----
>From: "Philip B Atchley" <[email protected]>
>To: <[email protected]>
>Sent: Monday, August 26, 2002 10:54 PM
>Subject: [R-390] No "Depot Dawg"
>
>
> > Hello again.
> > Well, today I pulled the IF and RF decks out of my "new" R-390A to start
> > recapping and refurbing them.  As it turns out, all modules (and rear
> > panel) are EAC with SN's ranging between 7125 and 9961.
> >
> > Knowing how the depots tended to just throw everything in large bins (or
> > whatever) and slap the R-390A's back together using whatever modules 
>were
> > ready to install, I highly suspect that this unit has never been through
> > depot maintainance.  The only thing not EAC is the PTO, which is 
>Collins.
> >  I may put the Cosmos PTO in this unit if I can get endpoints etc set
> > correctly.
> >
> > I got the transmission cleaned up really nice today (it wasn't very 
>grimy
> > anyway).  Removed all the coils and cleaned em, "Caiged" the sockets for
> > the coils.  Cleaned the roller bearings on the slug racks etc.  Got all
> > that back together and the whole mechanism is much, much smoother and
> > easier tuning now.  It won't go back in the mainframce until all the
> > modules are completed, just in case I "forgot" something.
> >
> > Question 1:  The RF and IF decks only have a couple of the "Brown
> > Beauties", which naturally will be replaced.  The rest are either flat
> > Yellow Aerovox units that "look" relatively modern, or the "West Cap"
> > metal/glass types. I've heard these were relatively reliable.  Are
> > they???
> >
> > Question 2:  I've used De-Oxit D5 on the bandswitch wafers in previous
> > restorations, but have since read (somewhere) that it can swell the
> > phenolic somewhat and cause trouble.  The Xtal Oscillator switch looks
> > like phenolic or bakelight (brown) while the RF deck switch wafers are
> > green (Fiberglass?) Any truth in this?
> >
> > 73 de Phil  KO6BB
> > Loving home provided for wayward Boatanchor Receivers
> > [email protected]
> > Merced, Central California
> > 37.18N  120.29W  CM97sh
> >
> > ________________________________________________________________
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>
>
>
>
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>End of R-390 Digest

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