[time-nuts] 5370B Question / help needed

Thomas Allgeier th.allgeier at gmail.com
Sat Jul 1 16:12:27 EDT 2017

I got hold of a 5370B cheaply but it turns out it may have a fault:

Going through the motions of measuring TI with it's own 10MHz ref as input
(as described in the manual) I don't get 100 ns, but around 15 ns. So this
is with the switch set to START COM. Oddly enough I get the same 15 ns with
the switch set to SEP, and going through a 6 ft cable between start and

Now I can "tune" the thing to display 100 ns by changing the trigger
levels. Start at 0.6 V and stop at -0.1 V will achieve this. Once again
this does not change by going from COM to SEP i,e. by adding the 6 ft delay.

One other observation, probably related: After powerup it took several
vigorous switch activations of the COM/SEP switch before the thing swung
into action at all - i.e. the first reaction with COM setting was an Err
02, and with SEP I got the 15 ns as described above. So that switch may be
a bit dodgy.

Measuring in frequency mode gives the 10 MHz quite accurately, less than
1mHz off with its own ref as stop input. Feeding the 10 MHz in from my
GPSDO also ties up OK, it is around 40mHz off with perhaps 5-10mHz jitter.

Has anybody come across anything similar? I couldn't find much in that vein
in the archive but may have overlooked something. The one thing I was
worried about at first was the heat sinks at the rear getting really hot
but it seems I'm not the only one with that observation.

To some extent it looks like the input levels for triggering are off, but
then the fact that the 6 ft cable don't show up as extra delay may mean
there is something else wrong.

Looks like some "fun with Bill and Dave" lies ahead if somebody can point
me in the right direction.

Thanks in advance,

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