HP 8568B, Battery Replacement

 

Recently, when I turned on my HP 8568B Spectrum Analyzer to make some measurements, the CRT was flashing text that read "BATTERY".

A quick search revealed that this meant a battery in the RF Section (the lower unit) needed replacing.

Googling around, I found a very useful YouTube video by CuriousMark describing some work he had done on his 8568B, including the replacement of the battery.  I've included his video, below.  Battery replacement is roughly 18 minutes into it.

Below are some additional notes of mine on battery replacement:

Notes on the Replacement Battery:

I used a 3.6V Lithium AA Battery manufactured by Tadiran (P/N TL-5104/P) and available from Digikey:

Installation was straightforward.  Just make sure not to short out the battery's leads on, for example, the metal chassis, while soldering it in place.

Notes on the Replacement Procedure:

The procedure CuriousMarc uses to replace the battery can be found starting on page 1-13 of the following HP Publication:

Title:  Installation and Verification Manual, HP 8568B Spectrum Analyzer Manual
Part Number:  08568-90119
Printed:  September, 1993

Download URL:  https://www.keysight.com/us/en/assets/9018-05833/user-manuals/9018-05833.pdf

Note that after the battery has been replaced, the Controller board's NVRAM needs to be cleared and reinitialized by first installing a jumper across two test points on the board (with the system powered down), powering up the 8568B (and verifying that the board's LEDs sequence properly with the jumper installed), then powering down the 8568B and removing the jumper.

The procedure states that this jumper should be connect the TP1-8 and TP1-9 test points together (Step 10).  My board (like that of CuriousMarc) only has TP1 pins that go up to 7.  

However, the signals that should be jumpered are actually on this earlier version of the board, they are just assigned different pin numbers.  So, instead of jumpering TP1-8 to TP1-9, you should jumper TP1-7 to TP4, as I've identified in the A15 component layout diagram, below:

(Note that the layout above came from the "Troubleshooting and Repair Manual," HP P/N 08566-90042, Printed December 1984).

After the NVRAM has been reinitialized, the 8568B must be recalibrated.  Fortunately this is straightforward.  Step 19 of the procedure describes this recalibration, but it can also be found in other HP manuals, too.  The one below is from the "Operating and Programming Manual," HP Manual P/N 08568-90041, pages 2 & 3.  

Note that this more verbose calibration procedure identifies what actually happens when the "Recall 8" and Recall 9" shortcuts are applied.

That's it.  The hardest part of replacing the battery was actually removing the 8568B from the shelf above my workbench.  It is a *heavy* beast, and I needed to remove each of the two sections separately to avoid giving myself a hernia.

Standard Caveat:

As always, I might have made a mistake in my equations, assumptions, drawings, or interpretations.  If you see anything you believe to be in error or if anything is confusing, please feel free to contact me or comment below.

And so I should add -- this information is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.