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

Wed, 28 Aug 2002 21:12:27 +0000

Hi Drew.
Yes, I found his remarks interesting (and educational).  But I decided to
just go ahead and replace them all with higher voltage capacitors for
reliability, especially since I had "most" of them in my box of parts
that I'd been holding onto for just such a receiver. I have the meter but
didn't really have a high Voltage power supply (unless I used the one in
the R-390A).  As I really do intend to keep this one this time I thought
I'd spend the extra time to do all I can to make it as reliable as
possible.

73 de Phil  KO6BB

> 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.
> >
> ky 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

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