[time-nuts] HP 5370a

[Matthias Jelen]

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.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
>>>
>>>
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