[time-nuts] SRS PRS10 problem

Brendan Minish ei6iz.brendan at gmail.com
Sat Apr 16 10:42:03 UTC 2011


Just a follow-up for others that may run into this someday

I took apart the PRS10 and disassembled the lamp assembly, Not easy..

I discovered that the MRF134 in there was still functional but that
there was a second short that was preventing oscillation, this looked to
be due to solder reflowing slightly from a joint to a chip cap had been
soldered with an excess amount of solder in manufacturing  

I removed this, tested the fet which was still ok but would be a real
bear to replace. I then tested each discreet component (ceramic caps
with LC meter, resistors etc) 
I put the lamp assy and the PRS 10 back together 

Now looking though the hole provided I can see that after a short warmup
the lmap now does light (it didn't previously)  however the unit no
longer locks to Rb 

I have shelved the PRS10 and rebuilt my reference around a Trimble
 thunderbolt. 
Perhaps at a later date I'll have another go at it 
thanks for all the help 




On Wed, 2011-02-16 at 22:37 +0000, Brendan Minish wrote:
> Interestingly it was not your normal tin whisker (I have seen a few of 
> those, just..) it was a substantial one that had grown out from the 
> stack of 2 Ceramic caps in series with the coil to the RF choke in 
> series with the DC supply to the lamp housing.
> 
> It might even have been a solder blob left over from production but it 
> looked quite crystalline.
> It's a bit ugly in the lamp assy because the heat and strong RF field 
> made a bit of a mess of insulation on the RFC and the heater leads but 
> everything else seems ok
> 
> I'll try and locate an MRF134 and see how I get on, certainly worth the 
> price and time by the sounds of it.
> 
> thanks for all the help and encouragement
> 
> On 16/02/2011 22:14, Pete Lancashire wrote:
> > http://nepp.nasa.gov/whisker/
> >
> > I've fixed two cell phones for friends and I have a very nice MP3
> > player I got for $1.
> >
> > Each was fixed with a stiff brush with a combination of compressed air
> > (outside) and
> > a vac inside.
> >
> > -pete
> >
> > PS if you do the air thing don't forget about static use a ionizer.
> >
> >
> >
> > On Wed, Feb 16, 2011 at 1:58 PM, Bob Camp<lists at rtty.us>  wrote:
> >> Hi
> >>
> >> Real solder has lead in it to eliminate tin whiskers.
> >>
> >> We're going to see a lot of stuff die in the coming years from these little
> >> critters.
> >>
> >> Bob
> >>
> >> -----Original Message-----
> >> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> >> Behalf Of Magnus Danielson
> >> Sent: Wednesday, February 16, 2011 4:55 PM
> >> To: time-nuts at febo.com
> >> Subject: Re: [time-nuts] SRS PRS10 problem
> >>
> >> On 02/16/2011 10:31 PM, paul swed wrote:
> >>> Well a couple answers.
> >>> If those are RB whiskers try the heat gun at 300 degrees on it for 15
> >>> minutes. As Magnus suggests and I just tried for the first time. It
> >> actually
> >>> worked and I recovered the rb lamp.
> >>
> >> While the heat gun on the Rb lamp is a nice trick, the whiskers most
> >> likely is nothing but traditional tin whiskers. A bit of re-soldering to
> >> remove bad metal and replacement of burned transistor is where I would
> >> start.
> >>
> >> Cheers,
> >> Magnus
> >>
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> 
> 

-- 
73
Brendan EI6IZ 




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