Got a 34970A with Error 741 - Cal data lost: String Data. The DMM surprisingly works and a quick check suggests it does fine, as missing cal data would result in it being way off. However, ignoring E741 doesnt help, the PC software refuses to work and just tells me about E741.
I did find a few posts that end up telling me i would need to replace 2 FRAM ICs and then send the unit in for a complete re-cal. Expensive option. Time to think about it...
Sooo, Cal data is stored in a FRAM 24x04A, one for the base unit and one for the DMM card.
Now, whats "String data"? And Where is it?
Disconnected DMM module -> Error is still there, no change at all. Very good! Theres should be nothing in the base unit that needs to be calibrated, so "String Data" couldnt be too important...
Unsoldered the FRAM (Careful! Its right next to the battery POSITIVE terminal, so remove (and later replace*) the Battery first), and read it out: Readable, not totally blanked. See attached _bad.hex
Now i got another working 34970 (official excuse: check and replace battery...) to read out its FRAM too, see _good.hex
Copied the "good" image to new FRAM and soldered in "bad" 34970: Boots up fine, no error! Reinstalled the DMM, also no further problems. Looks like a success...
It would change the serial number etc (maybe thats what "String data" is?) but who really cares...
Short:
Buy a Cypress FM24C04B-G, program 34970a_good.hex into it (any cheap I2C Tool works, its compatible to standard EEPROM 24c04), replace, done.