[time-nuts] [Summary] HP 115CR Clock Powerup / Documentation

Bob Camp kb8tq at n1k.org
Sat Dec 24 11:03:20 EST 2016


Modern tantalum caps get a bad rap. When you dig into the data, most of it relates to 
the “bad old tantalums”. What you have in these devices *are* the “bad old tantalums”. 
When they go, they can make both a massive mess and a real stink. 

The idea of keeping things “as built” in vintage gear is never a bad thought. A lot of fine
old gear has been trashed by “improvements” (some done by me …) over the years. 
In the case of wet slug tantalums (the proper name for these beasts), not
a real good idea. Replacing them with modern solid slug tantalum caps is a good idea. 
They have some “interesting” features in timing circuits, so replacing tantalum with 
tantalum is a good idea. Make sure you get the polarity right :)


> On Dec 23, 2016, at 8:50 PM, paul swed <paulswedb at gmail.com> wrote:
> Looks like you have great advice. But I will add if the tantalums show the
> corrosion do not fire it up. Unless you like smoke and other damage. A good
> way to extend the time you will spend getting it going and cleaning up the
> acid all over everything. Lots-O-fun.
> Good luck and I have always heard the mechanics were the challenge. No real
> experience.
> Regards
> Paul
> On Fri, Dec 23, 2016 at 6:24 PM, Hugh Blemings <hugh at blemings.org> wrote:
>> Hiya,
>> My thanks for the various replies including to Luciano for the 115BR
>> manual and Chuck for the timely advice about old caps!
>> I'll take a put at summarising the various replies and my own observations
>> now I've the 115BR Manual and the 115CR unit itself - any errors in same
>> mine alone;
>> The 115CR appears to be a slightly later device - it's 2RU rather than 3RU
>> and uses plug in PCBs rather than point to point/tag strip style
>> construction.
>> Based on a quick glance at the 115BR service manual and the 115CR unit
>> itself, I'd venture they are electrically and mechanically very similar,
>> possibly identical.
>> The 115CR seems to have hard wired DC input polarity relative to ground
>> wheras the the BR is switchable.  The 115CR doesn't have a meter or as many
>> frequency output options.
>> Maintenance wise;
>> * Divider circuits need to be manually started using internal switches,
>> the unit has built in rack rails to support easy access.  Similarly the
>> motor must be manually started.
>> * Many of the silver can (physically larger) axial capacitors on the PCBs
>> in my unit show signs of corrosion - this presumably the acid leaking out
>> of the tantalum caps as Chuck alluded to.
>> * One correspondent suggested replacing the caps right from the word go,
>> another to go for broke and turn it on - not sure which way I'll go yet ;)
>> * The mechanical odometer style display needs care not to bind up/jam.
>> Attention to lubrication/grease for the motor and other bearings seems
>> prudent.  Don't force any of the mechanical components.
>> * Looks like I can get a paper manual here http://www.etestmanuals.com/Se
>> arch.aspx?Search=115CR - I think this will be my next step.
>> I'll close for now with this quote from Chuck which may dash my plans to
>> have it on permanent operating display;
>> "These clocks are not a lot of fun to live with.  They sing along
>> quite loudly at 1KHz."
>> ...so might not be ideal in the otherwise quiet lounge room after all :)
>> Thanks again all for the input so far, will report further progress when I
>> return to the device in the new year after a house move :)
>> Cheers,
>> Hugh
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