There was some trouble with tapping-mode imaging this morning, and with Prof. Yang's help things seem to be straightened out now. I tried both NanoScopes with both MultiModes (we have two nominally identical systems), but had not bothered to swap heads. As it turned out, we had been using the infrared head (we have three heads), which wasn't working. Not that that was the only problem. As it turned out, tapping seems to be working with the combination
NanoScope 2 -- MultiMode 1 -- Head 1 or 2
As far as I can tell, the problem is generating the voltage for the piezo that vibrates the cantilever, which seems to take place on the MultiMode main board. Unless something is seriously wrong with the NanoScope, it shouldn't matter which NanoScope we use. I suppose I should trace the NanoScope-MultiMode communication in both cases and look for something different.
I've no idea how generating a tunable sine wave can be so complicated. The simple solution is to stick to modular equipment with open-standard, easily-accessible communication between them, but I don't have time to develop a system like that. Some day I will give up on NanoScope troubleshooting and build a GXSM system.