In October 2019 I bought a HP 35665A Dynamic Signal Analyzer on Ebay.
It was in nice condition but with only option 1D2 (Swept Sine Measurements) installed. See Installed_Options_Before_Upgrade.JPG below.
After checking the “HP / Agilent 35665A Options Upgrade” at
https://www.glkinst.com/test-equipment/ I was able get the remaining SW upgrades (1D0 - Computed Order Tracking, 1D1 - RealTime Octave Measurements, 1D3 - Curve Fit/Synthesis, 1D4 - Arbitrary Source and 1C2 - HP Instrument BASIC).
But there are two options, 1C1 and ANA, that can’t be installed via SW upgrade. The 1C1 option upgrade the 2 MByte standard memory by additional 2 MByte, resulting in 4 MByte, and the ANA option add another 4 MByte, resulting in the maximum 8 MByte memory. My instrument only had the 2 MByte standard memory.
When I opened the instrument and looked at the memory board (35665-66585) I could see that both the STANDARD RAM area and the OPTIONAL RAM area were populated with 16 circuits of M5M44256BL-10 (256k x 4bits, 100 nS). The memory mounted on the board is in total 16 x 256k x 4 bits that are arranged so they result in 2 MByte.
To be able to upgrade to option 1C1 the memory board has to be replaced by a 4 MByte board (35665-66586) or for the option ANA it has to be replaced by an 8 MByte board (35665-66587). After Googling for pictures on these boards, it looked like it was the same PCB but with different memory circuits mounted on them. On the 4 and 8 MByte boards they used 8 or 16 memory circuits of M5M44400AL instead. On these boards the 1M RAM jumper (R101) was also removed.
So instead of trying to find a memory board on Ebay I purchased 16 circuits of the M5M44400AL-7 from a dealer in China. (This component is no longer available from the well known component distributers. So I had to look at other places.) It can be a bit risky to buy components there. But I was lucky and got functioning components after a week.
After a tedious work of desoldering 16 x 26 = 416 pins and then solder the same amount of pins on the new components, I also removed the 1M RAM – jumper. The board no looks as shown in: 8MByte_of_memory.JPG. The startup showed that I now have: Main Ram 8.388.608 Bytes. See picture: Boot_up_after_Upgrade.JPG.
And finally I now have all possible options installed as shown in Installed_Options_After_Upgrade.JPG
I hope this information can be useful if someone else want to upgrade an HP 35665A. Hopefully there are plenty more of the M5M44400AL-7 memories available. If not I suppose it can be possible to make a small 8 MByte RAM board that can be soldered to the pads and glued / tied to the board. (Can be a fun project to design…)