[time-nuts] HP-5370B Running Hot...

Burt I. Weiner biwa at att.net
Tue Sep 14 14:45:38 UTC 2010

I'm not familiar with the 5370B and I may be way off on this, but I 
wanted to pass along some information regarding another piece of HP 
gear that I have which ran pretty hot, too hot in my 
opinion.  Hopefully this will save someone else from the same grief I 
went through.

I have a HP-3336A signal generator.  Shortly after I got it I noticed 
that it was running pretty hot.  I was assured by a few folks that 
they did indeed run hot and not to worry.  I did worry and discovered 
that some of the units had a much "beefier" heatsink than did 
mine.  I beefed up the heatsink but the instrument still ran pretty 
hot.  One day whilst I had my back turned on it the pass transistor 
in the power supply shorted and in turn took out most of the devices 
on the mother board turning the mother board into a wind chime 
vane.  I was fortunate enough to find another mother board, replaced 
it and it now was up and running again but still too hot in my ongoing opinion.

Here's what I discovered: On the rear of the HP-3336A are two power 
selector switches.  Instead of mine being set to 120 VAC I discovered 
they were set to 100 Volts.  I don't know why or how they came to be 
set at 100 VAC since the instrument came from a local engineering 
firm, not Japan.  Maybe somewhere along the way one of the switches 
simply got bumped.  Anyway, it was just one position off from where 
the combination should've been set.  Correcting the primary voltage 
selector cleared the heat problem and the instrument, with my monster 
heatsink, now runs quite cool.  So, for whatever little bit it might 
be worth, if you think it's running unusually hot, check the voltage 
selector switches on the rear and possibly the primary DC voltages 
into the regulators.

Burt, K6OQK

>On Sep 14, 2010, at 3:12 AM, "Charles P. Steinmetz" 
><charles_steinmetz at lavabit.com> wrote:
> > A friend just received an HP 5370B that was said to be properly 
> working and accurate, and asked my opinion.  I'm not familiar with 
> these, so I thought I'd ask the experts.  All we've done so far is 
> hook it to a Tbolt that I know is operating properly.
> >
> > The 5370B took hours (8 or so, which seems like a long time for a 
> 10811) to drift to a reasonably stable reading, a bit over 100 Hz 
> high (which seems like an awful lot for a 10811, even after a trip 
> across the country ten years since its last calibration).  The 
> front-panel oven indicator is off; I did not notice if it was on 
> when we first powered it up.  The 5370B reads its own oscillator 
> within spec (< 2 mHz error; spec is +/-5 mHz).  We have not opened 
> it to tweak the oscillator (or to verify that the 10811 is, in 
> fact, still present).
> >
> > Timing seems to work OK, giving the expected 100 nS and 50 nS 
> figures when I feed the internal oscillator into the start input, 
> tie start to stop (START COM), and switch the trigger phase of the 
> stop channel.
> >
> > Finally, the external heatsink (left rear) runs pretty darn hot 
> -- somewhat warmer than you'd really like to leave your hand on, 
> which is WAY warmer than I'd ever design.  Concerning (to me), but 
> not completely beyond reason.  I suppose it could be normal for 
> these.  It didn't burn down or shut off during the 8 hour warmup.
> >
> > I appreciate any input from those knowledgeable about the 5370B.
> >
> > Thank you,
> >
> > Charles
> >

Burt I. Weiner Associates
Broadcast Technical Services
Glendale, California  U.S.A.
biwa at att.net

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