My ST NVRAM came today. As previously reported it took 3 boots to clear the T1331 error.
I now have both the 11810 User Manual and Service Manual in original Tek hardcopy.
I experienced a good bit of operator confusion after performing the Enhanced Accuracy procedure from the service manual. In particular it seemed to be aliasing the calibrator output. But now I'm getting 26-32 ps rise times which seems about right for an SD-20 head.
I tried to copy the A5-U300 ROM but I'm not sure that succeeded. The TNM5000 said it failed to identify it. Can anyone tell me what type of EPROMs are used in the scope?
As much as I hate to take it apart again, I would like to archive the ROMs in case I or anyone else needs them. I'll also scan the User Manual.
I'd like to thank all who helped but especially Tom for the tip about removing the DS1213s, Adrian for procuring the NVRAM replacements, Albert for general guidance and the person who sent me a link to a PDF scan of the 11801 manual. I've tried in vain to find out the name, but I may not be looking in the correct place.
BTW the upper knob has a crack where it pushes over the encoder shaft which resulted in it slipping a lot. I put a piece of heat shrink over it and it seems to be working fine now. But if anyone has a replacement, please contact me off list.