HP 859x Spectrum Analyzers Bandwidth Filter Boards

[JohnK625]

If you get the dreaded "RES BW AMPL FAIL" message during a Cal procedure, you usually have to do the tune-up procedure on the Bandwidth filter boards (A11 and A13).

But almost the entire instruction for LC Centering (steps 25 - 29) in the Assembly-Level Repair Manual 08590-90316 for HP 859X series Analyzers is wrong.

I made a matrix of the jumpers and adjustments in Excel, which showed the problem clearly.

As written, it instructs you to first adjust the capacitor for A13-2nd LC Pole, then the one for A11-1st LC Pole, then for A13-2nd LC Pole again, then for the A13-1st LC Pole.  It completely misses the A11-2nd LC Pole capacitor.

And, in the case of the A11-1st LC Pole adjustment, unless you try to guess what they meant, as “stigwurx” did elsewhere in this forum, there are two open jumpers.

I’m amazed that the LC Bandwidth Filter works at all after this procedure.

I assumed that the correct adjustment sequence was the same as for the crystal filter, and wrote a clarified corrected instruction, which follows -
-----------------------------------------------------------------------------
25. Short A11TP10-11, A11TP12-13, and A13TP10-11 using the crystal shorts used in the crystal alignment section.  Press the following analyzer keys -
   BW, 30, kHz
   SPAN, 200, kHz
   MKR FCTN, MK TRACK ON OFF (OFF)
   BW, 100, kHz
26. Adjust A13C45 (A13 - 2nd LC) for maximum signal at center-screen.
27. Move the short from A13TP10-11 to A13TP12-13, then adjust A13C23 (A13- 1st LC) for maximum signal at center-screen.
28. Move the short from A11P12-13 to A13P10-11, then adjust A11C45 (A11- 2nd LC) for maximum signal at center-screen.
29. Move the short from A11TP10-11 to A11TP12-13, then adjust A11C23 (A11- 1st LC) for maximum signal at center-screen.
------------------------------------------------------------------------------
The A13 filter board is the one closest to the Power Supply.  The A11 is two spaces farther away.  The boards are identical.

Incidentally, the "shorting" jumper consists of a .01 uF capacitor and a 90.0 Ohm resistor, in series, with a header pin socket on each end.  The sockets should fit pins .025" (0.65mm) square, spaced 0.1" apart.  The capacitor can be +/- 10 %, but the resistor should be a 1% unit.  Cover the sockets with shrink tubing so they can not short the pin to the board slot cover.  The pins have DC voltage on them, and grounding them will cause damage to the circuitry.  You can do the adjustments with the cover plates removed, but it's a pain to remove and replace them.

Some more notes -
1) Do not neglect the "Amplitude" adjustments for both the Crystal and LC filters.  These must be right on, or the amplitude calibration will fail.

2) If you think you got the filters adjusted correctly, but the Ampl Cal still fails, check the Bandwidth Control lines to the two boards (BW5, BW6, and BW7 on the CLIP schematic).  Different voltages on these lines set the two filter boards for the different selected bandwidths.  A chart on the CLIP schematic for the Bandwidth Filter Board shows the expected voltages for these lines for different bandwidth selections.  An attachment at the bottom here shows the voltages and test points.

My voltages were wrong, and I had to replace one of the D/A converters on the Analog Interface board to fix the problem.

[Rik]

In the initial settings step 5 says "Press AMPLITUDE then use the knob to place the signal at the sixth graticule line from the bottom."

Are they counting the bottom line that is the outline of the screen as line 1 or are they counting the first dotted horizontal line as line 1? line

[Rik]

Following the manual and the suggestion in this thread my 8594E still will not reach 0 db in step 42. It then fails the CAL AMP test at the 1 kHz step.

I did determine also based on suggestion in this thread that my BW voltages were not stepping correctly. One was frozen at all BW's. I replaced the A7 board and the BW voltages are good now. But, even that did not correct the issue of the CAL AMP fail at 1 kHz, this the test stops there and does not complete.

Any suggestions?

[Rik]

R31 on A11 & A13 are at max.

[JohnK625]

Rik -

It's likely that one of the "shorting" network pins got shorted to ground and damaged the bandwidth selection circuitry on one the boards

If you have a spare BW board, that could be helpful.  They show up regularly on ebay.

[Rik]

I was careful to insulate my shorting plugs. But a prior owner may have had that issue.

I am going to look for a replacement board for the A11/A13 positions.