8594A spectrum analyzer "ref unlock"

[Bea973]

Hello all,

I have just received an 8594A spectrum analyzer, its condition is without comments and it passes the calibration phase without error.
Unfortunately the "ref unlock" error appears regularly (it does not appear permanently).
Do you have any ideas, have you ever encountered an error like this?

[Muxr]

A Spectrum Analyzer needs a reference clock to sync all its components to the same clock. 8594A uses a 10Mhz internal reference. But it also should have an output (on the back of the instrument, top left) where it provides this same reference as the output. You could measure the output reference and see if it produces 10Mhz clock consistently.

You can also provide an external 10Mhz (between -2 to +10 dBm) reference signal to the instrument  ("EXT REF IN", BNC connector) and see if that fixes your problem. If it does your internal reference is probably faulty.

[Wallace Gasiewicz]

Does the unlock appear when the unit is warming up? 
Do you have the option 004 precision frequency reference?  Should be a tag on the back of the unit.   
Precision references are commonly  oven oscillators and require some time to warm up before the unlock light goes off.   

[Bea973]

Hello,

Thank you for your quick reply.  In fact, I don't think I have a problem with the ref. generator, I checked the output of the reference signal (image attached) and it seems correct.

I have seen the following procedure in the manual but I wonder about the flashing error message, it seems to me that the procedure talks about permanent failure.
Also, the description of the measurements doesn't seem clear in the doc.
perhaps it's a known fault?

The battery is old and should be changed, but I don't think it's the cause of the problem.


1. Check the rear-panel cable connections for the 10 MHz reference.
When using either the standard 10 MHz timebase or the precision
frequency reference, make sure that the 10 MHz REF OUT on the
rear panel is connected to the EXT REF IN. The W6 jumper is
supplied with the analyzer for this purpose.
When using an external 10 MHz reference, make sure it is connected
to the EXT REF IN on the rear panel.

2. If the rear panel connection is correct, check the power output of the
10 MHz frequency reference.
• The A22 standard 10 MHz timebase (RTXO) has an typical
output of 0 dBm ± 6 dB.
• A22 precision frequency reference (OCXO), has a typical output of
0 dBm ± 3 dB.
• An external 10 MHz reference should have an output between
-2 dBm and +10 dBm.

3. If the output of the 10 MHz reference is correct, check the continuity
of W18, the EXT REF IN cable, and W17, the 10 MHz OUT cable.

4. Check the continuity of the VTO_TUNE control line.

5. Check the continuity of the W14 ribbon cable and the W21 coaxial
cable.

6. Check the continuity of the A25 assembly connections to the A9
assembly that pass through the A15 motherboard.

7. If the error message is still present, suspect the A25 counter lock
assembly.

[Bea973]

[ Specified attachment is not available ]

Hello,

No, even after a long time (1hr), the message continues to appear.

[Wallace Gasiewicz]

Yes, the ref osc is definitively putting out the appropriate signal strength. 
A long shot but try a BNC jumper from the ref osc to input.

[cncjerry]

swap the short cable on the back.  while doing that, measure the output of the oscillator on the reference output connector and see if it is stable.  If it is stable, then open the unit up and carefully reseat the w14 cable with power turned off, of course.

The other thing you can do is put a stable signal into the unit, put it on max hold(?) can't remember what it is called, but you want to hold the maximum signal on the display.  If there is a lock problem with the ref, then your stable signal will be moving around and you will see the held signal get wider. 

I assume you don't have a stable reference to inject?  You need something that is disciplined because if the reference moves around that will unlock it too.

Someone above mentioned taking the reference output and bring it around to the front and take a look at it.  It should be stable and the proper level.

Jerry