I have an 8647A with a dead battery circuit.
Do you know if your calibration is still valid or can you check it?
I found a calibration ROM in the 864
8 block schematic in several assemblies (A5 Sig Gen Synth, A6 Output, A7 Attenuator). But that's true for the 864
8 not necessarily for the 864
7...
I couldn't find any schematic or block schematic for 864
7.
The 864
7 has some error codes (503-512) of type "failure in comparing calibration data
between RAM and the calibration ROM, a data restore was done" type, as listed in the Operation and Service Guide [08647-90006].
That could mean the cal data is stored basically in EEPROM in several assemblies and is copied to normal (volatile) RAM at startup, so the cal data would not be corrupted by potentially empty RAM backup battery.
But I'm not certain about that...
I still don't have any error message at start up, but I want to exchange the old battery.
If just the device settings were stored in battery-backed RAM it would not risk to completely brick the device.