[time-nuts] HP 5065A rubidium lifetime

[John Miles]

One big favor you can do your 5065A is to check the ESR of the electrolytics
on the A11 oven driver board.  C23 and C24 were open on mine, as was the
other instance of the same 20 uF cap on the battery-charger board, and the
lamp driver assembly had experienced overheating to a point that was
sufficient to char a resistor and crack it open.  I'm not sure how, or if,
those two caps would cause total control-loop failure, but there was
apparently nothing else wrong with this unit that could explain the
overheating.

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of paul swed
> Sent: Friday, March 19, 2010 5:14 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP 5065A rubidium lifetime
>
>
> Corby,
> Interesting on the melt down. Is there a reason to consider a
> second safety
> device somehow?
> I would hate to loose the 5065 because of a run away heater.
>
>
> On Fri, Mar 19, 2010 at 5:10 PM, Corby Dawson <cdelect at juno.com> wrote:
>
> > I have been repairing HP 5065A for over 20 years and have never had a
> > failure due to "darkening"
> >
> > I did have one Efratom unit years ago that the lamp envelope
> had darkened
> > so much it was unusable.
> >
> > Not sure if the is the "darkening" referred to?
> >
> > The "killer" 5065A failures are oven failures that melt the insides, and
> > a bulb that has a very low output. (The bulb envelope is still nice and
> > clear in these cases.)
> >
> > The bulb can be replaced with some Efratom ones with varying results.
> >
> > Also cell flooding can occur after long storage and/or storage in high
> > temperatures.
> >
> > This is easily cured by applying 5VDC thru a 5ohm 10watt resistor to the
> > TED (thermoelectric device) in the receiver for 6 days or so.
> >
> > Corby Dawson
> > ____________________________________________________________
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