Solved: Agilent 53131A, 53132A 12.4 GHz option prescale defaults vs eeprom/bits

[EE4all]

I have a 53132A that I have added a China sourced 12.4 GHz module to. This works, but a scale factor of 2 must be added. Upon adding a zero ohm resistor to R334 pads, it still works, but I need to enter a scale factor of 4. It is not clear to me if an original Agilent 12.4 GHz option also requires manual entry of a scale factor, but I highly doubt it. Internet posts that I have found about adding such an option declare that, "it just works," but they do not mention if a scale factor needs to be manually entered.

I also have fully followed post 22 of the following thread, https://www.eevblog.com/forum/testgear/hp-agilent-53131a-53132a-53181a-12-4-ghz-option/ but changing those 3 hex values in the eeprom didn't change anything. So coming to my main question, how does one program the unit to know to use the x4 multiplier on channel 3, so that I do not need to manually enter a scale factor?

[EE4all]

Here is the eeprom, now with a socket. 

[TheSteve]

No scaling factor should have to be manually accounted for. There may be a minimum firmware version required.

[EE4all]

I tried this with firmware 3944 and also 4613.

Also, I note that my U14 eeprom from original 3944 and subsequently with 4613 never contained the header line specified in the earlier thread instructions as below. This leads me to wonder if that was from an earlier firmware in use at the time those instructions were written, and perhaps the bit positions I need to change are now different. I really do not know.

 5) Validate that header of data says 'HP53131 is a winner!' (it says this for 53131A/53132A/53181A)

[EE4all]

Also, posts 31 and 32 of the earlier thread have me wondering if additional pull up or down is needed on other pins of J7, besides the one impacted by R334.

[mankan]

I have 53131A that came with the 3GHz option, running FW 3703. I've upgraded to Cojotech 10GHz option. I do not need to set any scale factor nor is R334 mounted.

[EE4all]

Unfortunately, Cojotech is currently sold out. Thanks for the confirmation on no scale factor needed.

[EE4all]

I came to the conclusion that it will be easier to just pick a prescaler that doesn't need to use a scale multiplier. I picked one of those, also from China. Due to their New Year, it will take a while before I receive it. I chose one that goes to 10 GHz, as it seems all of them that go higher use the scale multiplier. This is good enough for my needs anyway.

[EE4all]

Ok, so not being able to resist figuring this out, I now have been able to flash my U14 EEPROM with changes needed to allow the 12 GHz prescaler to work without a scale value being needed. The earlier posted instructions are probably correct, you WILL need a copy of U14 that starts with "HP53131 is a winner" near the beginning. Mine did NOT have that and/or whatever other bits are needed, despite having added the ones listed in the earlier post. To get this working, I added a U14 socket to a counter that already had a factory 12 Ghz prescaler, read out the chip, and then burned one for my other counter. Of course this then needed a quick recalibration. 

I guess when the 10 GHz one that I ordered shows up, I will sell it or stick it in a 53181a that I also have.