[R-390] Capacitor replacement when restoring

Thu, 10 Jan 2002 02:17:18 -0500

Bill, that is the course which I am taking. I have found the same problems which
you have faced. Do 'em all, and you have an xcvr worth running and aligning. I
also am not letting the resistors slip by...they are all getting checked for
resistance as some of those older multiwatt ones do cause problems,
73 es tnx
de Greg WA3IVX

Bill Smith wrote:

> My understanding is it varies with manufacture of the unit.  Others can give
> you better details.  For example, my R-390 is filled with "Vitamin Q" caps,
> which are reputed to be of excellent quality and generally do not need
> replacement.  I have tested a few and have found this to be the case.  Thus
> most of the caps in this receiver are original.
>
> In the R-390 (non-a) here, which is apparently a late Motorola model, S/N
> 4700, I have had problems with mica capacitors.  Micas are generally very
> reliable, but the "pink, square" style in this receiver look like they are
> candidates for further examination.  I have replaced three, and believe
> there are others needing replacement in the RF stages.
>
> The AVC caps, C546 and C547 (1 mfd, located in the IF section near V511 on
> the schematic) have a reputation for leakage.   I disconnected one (they are
> in parallel) and gutted other case and replaced the insides with a 2-Mfd.
> cap.
>
> Generally, many capacitors in the .0005-.5 MFd range are constructed of
> paper and aluminum foil.  They become leaky and/or open with age.  Bath-tub
> capacitors (not in an R-390 as far as I know, but popular in other
> receivers) are now showing up leaky.  Performance really depends upon
> manufacture, with Sprague paper "Black Beauties" notorious as requiring
> replacement.   Any wax covered capacitors are known offenders as are many
> molded plastic capacitors
>
> As another general statement, one should NEVER turn on any equipment that
> has been on the shelf for 5 or more years without bringing up the set using
> a variac.  Hitting the set with 120 VAC is a good way to guarantee that
> electrolytic capacitors in the power supply will need replacement.
>
> In short, capacitors can be generally considered suspect.  In most receivers
> replacement of all cylindrical capacitors is appropriate, with a watch on
> micas.  Filter electroytics may often be recovered by reforming using a
> variac.  While you are at it, make sure to test resistors.  Typically, 10%
> or more of the carbon types in the set will have drifted 20% or more higher
> in value and should be replaced.  I found several open resistors in the
> R-390 power supply circuit.  The power supply was non-operational until the
> resistors were replaced.
>
> 73 de Bill, AB6MT
> [email protected]
>
> ----- Original Message -----
> From: "Gregory W. Moore" <[email protected]>
> To: "Boatanchors Reflector" <[email protected]>; "Eico Reflector"
> <[email protected]>; "R390 reflector" <[email protected]>
> Sent: Wednesday, January 09, 2002 3:38 PM
> Subject: [R-390] Capacitor replacement when restoring
>
> > Ok, I realize that this is a simple question, and I should already know
> > this, but WHICH
> > caps beside the electrolytics should be replaced when doing a total
> > rebuild/restoration?
> > I am now doing an Eico 753 but will be following shortly thereafter with
> > my R390A.
> >
> > Do I have to worry about the ceramic disks? They all test good with the
> > Fluke DVM , and otherwise look ok. What I sm conserned about, besides
> > the electrolytics are the silver mica, the molded silver mica, and the
> > mylar ones.
> >
> > Any info here is appreciated...also, if someone has a male Amphenol MC2M
> > plug, or prefably 2 of them...I wouldnt complain if they had the
> > matching receptacle as well, let me know.... I do want to get this thing
> > back on the air ASAP. Yes I do have a second, and works reasonably well,
> > but I am doing a complete teardown and restore on the first.
> > 73 es tnx
> > Greg WA3IVX
> >
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