In some miraculous way, my Agilent 54845A turned into 54845B (at least so it is now shown).
I made a motherboard update and a software update v.4.5 for 54845B. I tried different versions of software, but only with this I got success.
Previously, there was an Atlas PCI-III Series 757 motherboard based on Socket 7 and AMD K6-2 300 MHz processor and 64 MB RAM.
Now the most advanced motherboard for AT-form factor with Intel 440BX chipset and Socket 370, with 133MHz bus, where the Coppermine core Pentium III processor can be installed, up to 1133MHz (or with a small upgrade of Tualatin 1400MHz) and 3x256 MB of RAM max.
The new motherboard is designated Tomato (ZIDA) 60-cbxict1
Next to her on the photo is an old motherboard Atlas Series 757
I also had to replace the Ethernet controller for the PCI slot
At the moment I used a P III - 733MHz processor.
Subjectively, now I noticed a significantly smaller loss of the frequency of updates to the oscillogram in the mode of activation of measuring functions, than it was before.
p.s.
Now I found information that the manufacturer installs in the 54845B motherboard "VP22 Motorola" (Socket 370) and processor Celeron/Pentium III - 866 (Coppermine). Thus, we can assume that I received the same without changing the form factor AT. The only difference is that I still do not have a built-in CD-ROM, but it's not required too often.