Re: HP 8567A YTO Unlock message!

Hi
Thank you for your answer.
To correct my self :)) rear input of external 10MHz ref is on the RF
unit and not on display... I've done some more tests...
Switched on external reference and checked with a +3dbm 10MHz sinewave
.. When i applied the +3dbm signal it works like with the switch on
internal position. When i removed the signal from input, all system
freezed... So the internal ref must at least works. Dont know about
the freq accuracy of it yet (I'll measure it), but its working. So
thats good.

Glenn <Glenn@xxxxxxxxxxxx> wrote in message news:<nxnpe.3403$W51.23266@xxxxxxxxxxxxxxxxx>...
> I don't remember well and I don't have a set of schematics in front of me,
> but a couple of suggestions:

Do you have the service manual of the 8567? If you have it, can you
make some copies of specific parts of it (I'll pay all the cost for
them of course)?

> It's unlikely that you are running without *any* 10 MHz reference.
> Normally the 10M tuning range is only a few ppm.

Yes thats should be true. However I still cannot locate a 10MHz TCXO
inside that instrument. Have download some service (verification &
adjustment) informations for the bigger brother of it (the HP 8568)
and at the chapter that reffers to the 10MHz time base has a figure
showing the location of the A27A1 (10MHz TCXO). The strange is that at
my HP 8567A there is nothing there!!! Only empty space with some nuts
to install something and a PCB text near it saying A28 BATTERY... I'm
starting to believe that thats one of the differences between the two
models... Not sure however, but there isn't a 10MHz time base at the
suggested location. It might be installed on a different location?

> The YTO loop, (the "outer loop") probably needs several other properly
> locked references to operate correctly. In fact, it's "YTO unlock" error
> may only be a logical OR of inner loops. The idea being that if any of
> those other loops are not locked properly, the YTO signal cannot be
> trusted either. Oven Cold and Ext Ref are certainly affiliated with the
> precsion 10MHz reference and probably a detector circuit that looks for
> 10MHz external signal.

Oven Cold and all other messages except the "YTO unlock" are only come
on during the error correction routine. At normal operation mode, only
"YTO unlock" & VERY slow refresh rate of sweep are the symptoms. Even
at that refresh rate can make measurements of an input signal... I
understand the YTO loop as you explain it. The strange thing is that
during the test mode almost all measurements of inputs signals are
correct both for frequency and amplitude. I have also checked an AM &
an FM modulated carrier up to 1250MHz. And I say almost because I've
noticed that when I set a Span <1.000MHz cannot find the input
signal. Increasing again the span at >1.001MHz signal appears again...

> Are there rear panel BNCs on that instrument with adjacent "10M out" and
> "10M in" labels that should have a short jumper cable that is missing?
> That might almost explain all of your problems.
There is a BNC for 1st Local out and another one for frequency
refference IN/OUT depending on an INT/EXT switch aside of it. I've set
it on Internal position under normal operation.

> The slow refresh rate is probably related to error reporting of the
> unlocked condition. It will probably go to normal rate once all the loops
> are properly closed. I wouldn't be surprised if test mode ignores the
> warnings so that diagnosis can proceed more or less normally.
> Glenn

Yes thats true as I've read that during error corection routine some
signal flags are ignored!
Well I must found a manual now!
Any other suggestion will be excellent...
My regards
Sotiris pdmtr
.

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