The problem is that the whole VCO is packaged. The
connections from the VCO to the outside world are fairly
simple: -5,2 Volt, a bias for the buffer amplifier, the
tuning voltage and the start/stop line. The start/stop line
is tied to gnd with 2.2 µH, so even if the start/stop
circuit woud fail I can´t see how the oscillator could be
kept from oscillating permanently.
Anyone successfullly opened such a package (without damaging
it permanently?)
Regards,
Matthias
Am 05.07.2015 um 07:54 schrieb Bruce Griffiths:
On Saturday, July 04, 2015 05:20:45 PM paul swed wrote:
Matthias
I am afraid I am not much help here.
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..
No its microstrip within the VCO package. Other coax delays are used in
the oscillator turnoff and mixer logic.
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.je...@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
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