[time-nuts] Questions about HP 5370B

John Miles jmiles at pop.net
Tue Sep 14 08:23:07 UTC 2010

> Yes, the rear heatsink does run very hot, approx. 61 deg C. But
> do make sure
> the fan is running! The unit will be damaged without the fan. Also it's
> important to refrain from running the instrument too long with
> its top cover
> removed, because the fan air doesn't properly loop around and
> blow back out
> the heatsink if you've left the instrument top cover off.

There are no such concerns with the 5370B as far as I'm aware.  Nothing in
there runs very hot except the linear regulators themselves, which are
externally heatsinked.

It does sound like the 10811's oven fuse is open, though.  (The counter
won't work if there's no oscillator present at all.)

> As Bruce suggests, you'll want to peek inside to see that you
> really do have
> a 10811 oscillator. If so, then it sounds like the thermal fuse
> (F1, inside
> the 10811) might be open. According to the manual, I think the HP part
> number for F1 was 2110-0617. However, Agilent's current online
> parts search
> does not find that p/n. Maybe you'll have to call Agilent's "Parts ID" to
> identify the current part number for F1?  ...Or probably others in this
> forum will offer more current information regarding what part to

Just short it out, or if you like, put in an NTE part with a similar temp
rating.  It serves little or no useful purpose.

-- john, KE5FX

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