HP 8567A YTO Unlock message!

[pdmtr]

I have a HP 8567A (very similar to HP 8568A/B) spectrum analyzer that
has an error code flashing every 2 seconds on screen. "YTO unlock"
message comes on and at the same time the Green SWEEP Led on the 85662
Display unit flashes instantly. I have figure out that this is related
to the Yig Tuning Oscillator (Y.T.O.) that is the main sweep osc of the
spectrum analyzer. Inside the RF/IF section I have seen that the A6 YTO
PHASE LOCK board has the "YTO UNLOCKED" led permanent on while the "YTO
LOOP CLOSED" led is mostly lit and goes instantly out (whenever the
message on screen comes on). The exact same off time of it the "LOW"
led located on the A22 FREQ CONTROL Board comes on. The analyzer has a
sweeped display with a VERY low refresh rate (a refresh every time the
error message comes on) and has a working RF input, checked for level
with a R&S SMS generator... I can see the R&S output signal but
spectrum show a difference on carrier frequency of aprox: 13.6MHz lower
than the actual input freq. The 100MHz are showing (using the MARKER)
as 86.4MHz!
Anyone know something about that problem? I cant find even the manual
of the HP 8567A spectrum analyzer (while i have found where to buy the
manual for the 8568A/B model), so any help will be greatly appreciated.
My regards
Sotris Pdmtr
pdmtr@NOSPAMyahoo.com

 

[pdmtr]

Hi
Thanks for the reply.
Well I have put it on test mode yesterday (pressing "SHIFT" + "w") and
the analyzer worked with a normal refresh rate!!! Made some test on the
measurements it makes and ALL of them are inside specs!!! Correct
frequency accuracy of the applied signal from the R&S generator,
correct amplitude level, all buttons reacting instantly on pressing
(before they reacting every YTO message flashing time)!!! Problem is
that the error messages are still there. And I have more now! Except
"YTO unlock" I have also "Oven Cold", "EXT REF" (thats the most strange
as I have put the INTERNAL REF switch right!!!), and 2 more related to
the YTO unlock message!
Trying to figure out if thats a hardware failure of the YIG Osc, or a
failure of the ,master time base TCXO, as it looks like only the
refresh rate is "blocked" or delayed for some reason. But also it might
be a mis-programming fault, and not a hardware failure... Also I'm
thinking that the error it may be located on the 85662 display unit and
not on the RF/IF base unit, as it looks that the display unit provides
the RF unit some synchronizing signals thru the Bus cable and also some
IF signals thru the Multi-Coaxial Interconnection. Not sure where the
main TCXO is located, but it looks its on the 85662 unit and not on the
RF/IF base... So if the refresh problem is related to the locking of
the YTO that will lead to a TCXO REF fault. The EXT REF input is
located on the 85662 unit and that guide me to think that the INT REF
TCXO is also based on this unit... as it would be strange to pass a
10MHz signal input from the upper half to the lower half!
I've found the User guide of it and maybe I'll buy a HP 8568 service
manual, and try to see the relationship between failure on these model.

If you find something related (anything really) it would be a great
help, as the basic working philosophy behind the 8568 (8567) & 8566
Spectrum Analyzers should be the same!!! )
My best regards and good luck with yours also...
Sotiris
Pdmtr
@ (Nospam)YAHOO.COM

 

[pdmtr]

Also for your equipment may be it should be usefull to download this:
http://www.home.agilent.com/DEger/nav/-536892724.536881696/pd.html
and also look that one:
http://www.home.agilent.com/DEger/nav/-536892724.0/pc.html
Regards
Sotiris Pdmtr

 

[Sotris]

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@this.isnt.it> wrote in message news:<nxnpe.3403$W51.23266@typhoon.sonic.net>...

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

 

[Sotris]

Hi John
Thank you for the follow up message. Please read also my other answer
to Glenn.

John Miles <jmiles@pop.removethistomailme.net> wrote in message news:<MPG.1d0fa1945a09de139896ca@news-central.giganews.com>...

In article <1118153600.092161.134340@g47g2000cwa.googlegroups.com>,
pdmtr@yahoo.com says...
Trying to figure out if thats a hardware failure of the YIG Osc, or a...

It sounds like a problem with the diagnostic circuits. Or: "Oven Cold"
could imply a bad oven-control circuit in a 10811 OCXO module, if it has
one. That's a pretty common fault, usually caused by a thermal fuse
that's opened up due to old age.
I'd be somewhat surprised if the 8567A had a 10811 OCXO, though. If it
has a TCXO with no oven, then the presence of the "Oven Cold" message
makes me wonder if there's an interconnect problem between the 8567A and
85662A. It shouldn't be possible to get that message on an analyzer
without an oven-controlled timebase, so that'd be an important clue.

About the Oven Cold message I reffer at it on reply to Glenn. It only
displayed running the "Error correction routine" mode.

It's almost certainly not the YIG oscillator, if the analyzer works OK
in all spans in Shift-w mode.

Well I've found that at narrow span modes (<1MHz) there is a
problem...

But also it might
be a mis-programming fault, and not a hardware failure... Also I'm
thinking that the error it may be located on the 85662 display unit and
not on the RF/IF base unit, as it looks that the display unit provides
the RF unit some synchronizing signals thru the Bus cable and also some
IF signals thru the Multi-Coaxial Interconnection. Not sure where the
main TCXO is located

It'll be in the RF section.

Yes it should be there!!! Only thing is I cannot find it! )

, but it looks its on the 85662 unit and not on the
RF/IF base... So if the refresh problem is related to the locking of
the YTO that will lead to a TCXO REF fault. The EXT REF input is
located on the 85662 unit

Hmm, are you sure? That should be on the RF unit, not the display unit,
if I remember correctly.

Nope, you're right, I've corrected that already... )

If you find something related (anything really) it would be a great
help, as the basic working philosophy behind the 8568 (8567) & 8566
Spectrum Analyzers should be the same!!! )

Will do.

-- jm

------------------------------------------------------
http://www.qsl.net/ke5fx

My major problem is that here in Greece we don't have a lot of HP
support and to find something (used or not) we must take our chances
with the "SLR" (shipping lose risk) parameter as I call it Have
allready lost 3 manuals for test equipments ordered from US and
another one delivered to me after 5 months from shipment!!! And mostly
here, there is a total lack of (second hand) spare parts sources for
things like test instruments...
I have seen in the past, your tracking generator for the 8566. Nice
mod you've done there on the 86222A plug-in. Will something similar
work with 8567A/8568?
My best regards to all that helping at anyway...
Sotiris Pdmtr

PS. any follow up message is welcome