[R-390] RF Deck B+ short (390A)

[Dennis Wade]

Thanks Grayson.  Just a little more background...the receiver was in daily
use until one day it just started blowing fused.  I had the same impression
about resistors which is why having a good C308 made be expect a 2.2K
reading (or higher), not 60 ohms.

                D.

On Wed, Nov 19, 2014 at 11:48 AM, Grayson Evans <wa4gvm at gmail.com> wrote:

> Hi Dennis,
> I agree, make sure you remove the tubes, there could be an internal short
> in a tube element.
> All the coils are “isolated” from B+ by resistors of fairly high value
> compared to 60 ohms, but it would not hurt to see if turning the band
> switch changes anything.
> When resistors are damaged, they usually go UP in value, so I would not
> expect a bad R.
>
> I would trace the B+ line from where it comes in on J208 through the
> chassis and disconnect it someplace in the middle of it’s run to help
> isolate the low resistance.
>
> This could easily be a pinched B+wire someplace.
> I am overhauling my RF chassis as well, it happens to be on the bench
> now.  I was replacing some caps and giving it a clean.   I will poke around
> and see what looks like a likely suspect.
>
> Grayson,
> KJ7UM/TA2ZGE
>
> On Nov 19, 2014, at 8:59 PM, Dennis Wade <sacramento.cyclist at gmail.com>
> wrote:
>
> > Thank you all very much.  I've already isolated the short to the RF deck
> > with the unplugging modules technique.  I will pull the tubes and do the
> > measurements possibly tonight, more likely tomorrow night.
> >
> >       Thanks again....I love this list.
> >
> >                Dennis
>
>


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      - A. Alan Post  1914-2011.  California Legislative Analyst 1949-1977.

-------------------------
Dennis L. Wade
KG6ZI
Carmichael, CA