[time-nuts] HP 5370a

[Bruce Griffiths]

No the oscillator frequency determining delay line is a microstrip line on a 
ceramic substrate. The coax delay lines are used for not critical delays in 
the delay line vco start and stop
On Saturday, July 04, 2015 05:20:45 PM paul swed wrote:
> Matthias
> I am afraid I am not much help here.
> inted I did look at the a19/20 interpolators. A lot going on in that small 
space.
> I guess i would check the 200 MHz feeding into it. The VCO is fairly simple
> in using a gate and a delay line. I will guess the delay line is coax..
> But there are all kinds of gates to control the system and Flip Flop used
> as a mixer. Not easy to deal with.
> Regards
> Paul.
> 
> On Sat, Jul 4, 2015 at 1:44 PM, Matthias Jelen <Matthias.Jelen at gmx.de>
> 
> wrote:
> > Dear Time-Nuts,
> > 
> > I´m still struggling to get my 5370A to work reliable again. It keeps
> > showing error 04.
> > 
> > Sometimes it is working without any problems for hours, sometimes it
´s a
> > matter of minutes until the error is displayed, and sometimes I doesn
´t
> > come up without the error at all. I don´t think it´s related to
> > temperarure, the usual procedures with a hairdryer and cooling spray
> > didn´t
> > show any effects.
> > 
> > I dug into this a bit. It seems like the startable VCO on one of the
> > interpolator boards isn´t working reliable anymore. The error stays 
with
> > the board, no matter if I put it into the slot for the start channel or
> > the
> > stop channel. If the unit is in the non-working-state, there is no RF at
> > the output of the VCO. As soon the VCO oscilates, the PLL locks and
> > everything works fine, only the tuning voltage is a bit outside the 
range
> > given in the service manual. If the VCO stops oscillating, the tuning
> > voltage runs to it´s lower rail, just as expected. I opened the PLL loop
> > and tuned the VCO with a external power supply, this works as 
expected -
> > no
> > regions in the tuning range in which the oscillator stops working or
> > similiar.
> > 
> > I checked the signals going to the board, and they all look OK.
> > 
> > I fooled the logic that detects a tuning voltage outside the allowed 
area,
> > and as expected, the error 04 isn´t displayed anymore, but also as
> > expected
> > the unit still stops working.
> > 
> > I pulled the board, removed some components and supplied power to 
the VCO
> > from an external power supply - same behaviour here.
> > 
> > So I came to the conclusion that the VCO itself is defective, although I
> > have no idea what could cause a VCO to behave that way.
> > 
> > Now for the strange part: A noble member of this list sent me a spare
> > interpolator board which was pulled from a working unit. This shows
> > exactly
> > the same behaviour! Also at this board the tuning voltage is outside 
the
> > given window, and the oscillator doesn´t start from time to time.
> > 
> > If a dead VCO module is a common problem, I´d expect that someone 
on this
> > list also experienced this problem before. Otherwise, I think it´s
> > unlikely
> > that I found two defective interpolator boards in a row. I stil have the
> > feeling that I´m overlooking something simple. So `d be happy to 
receive
> > any comments on this. Also, if someone wants to get rid of a 5370 
that
> > needs repair I might be interested.
> > 
> > I guess this is what you can expect if your´re using test equipment 
which
> > was introduced before you were born, but it´s part of the fun...
> > 
> > Thanks,
> > 
> > Matthias
> > 
> > 
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to
> > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the
> instructions there.