[time-nuts] HP5065A Rubidium questions: some progress

[paul swed]

That actually sounds like good news.
The lamp will light and its a purple orange. Not sure how safe it is to
look at. Hmm but I have carefully.
If you have a scope the oscillator runs at 150 MHz +/-20 MHz its not fussy.
You only need to get the scope probe close to see the RF.
But likely its not running and its down to good old trouble shooting. Not
uncommon to have solder issues. These are old and have been cooked for ages.
May just need some serious TLC.
But you seem to be headed in the right direction.
Regards
Paul
WB8TSL


On Mon, Feb 20, 2017 at 7:25 PM, David Scott Coburn <scotttt at optonline.net>
wrote:

> Hi All,
>
>
> Thank you all for the very helpful suggestions!
>
>
> I will try to reply to you all in this one post.
>
>
> I opened up the A12 assembly and was happy to find that the lamp, windows,
> and reflector all appear to be in good physical condition.  There is some
> very light corrosion on the aluminum reflector, all of the windows are
> clear, and the photodiode is very visible at the bottom of the oven.
>
>
> The Rb bulb looks very slightly darkened, maybe like a pair of very
> lightly polarized sunglasses.
>
>
> I measured the resistance of the 20 VDC supply line to the lamp oscillator
> and it is 3350 ohms, just as Corby said and as I see it should be from the
> schematic.
>
>
> I measured the current to the lamp oscillator and it is only about 13 mA.
> Paul mentioned that if it was about 15 mA it was probably not working.
> And, Poul-Henning mentioned that it should draw about 3W when working,
> which at 20 VDC would be 150 mA.
>
>
> I powered up the lamp oscillator with it on the bench and I do not see any
> light from the bulb.  I am assuming that it should be visible, but I'm not
> sure!  What is the spectrum from these lamps like?  Visible, UV???
>
>
> I measured the resistance of the small coil wound around the bulb, it is
> about 0.3 to 0.4 ohms, which seems reasonable.
>
>
> (It looks like someone has been in this assembly before.  There is solder
> flux on the transistor leads, the 20 VDC connection, and the bulb coil
> leads.)
>
>
> One odd bit is that the resistor in the transistor emitter leg measures
> about 350 ohms (this is R3 in my schematic).  The schematic says it should
> be 10 ohms.  This resistor is on solder posts, so it looks like a 'selected
> at assembly' item.  Corby: it this the 12 ohm resistor you mentioned?
>
>
> The voltage across this resistor when the power is on is about 1.6 V.
>
>
> The base voltage is about 2.2 V (this is across CR1 also) and shows
> "flat-lined" on my scope with the board powered.
>
>
> So, I'm betting that the collector of the transistor is cooked.  (The
> base-emitter drop of ~0.6 V probably means the base and emitter paths are
> still OK.)
>
>
> But, it is also possible that the R3=350 ohms is way out of line??
>
>
> Comments welcomed.
>
>
> Corby: the serial number for the unit is 0968A00302.  It has a 105-6012
> quartz oscillator, and a mechanical PP clock.  The A12 unit is a series
> 1220, and is green in color.  (The OCXO and the bands around A12 are blue.)
>  The A12 unit has a warranty expiration of 30 April 1978.  It has had its
> "Mag Filed" and "Thumbwheel" blacked out with marker and new values written
> in.
>
>
> Cheers,
>
>
> Scott
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