[volt-nuts] Update on 720A

[David C. Partridge]

I can't replace the bad resistors in the A decade - they are in the oil bath and the manual says that in this case you sent the unit back to Fluke for a re-build.   These days, I suspect they won't even do re-builds at all (or only at *silly* money), but make you buy a new one, and may well not supply *any* parts unless they do the repair (as happened to a friend of mine with another instrument).

I'm really not convinced that "the very act of replacing the resistors is likely to cause additional damage" - I've been around delicate and high-Z electronics for a while now and can get in and out in unsoldering pretty handily.  I'm also very aware of the critical importance of not messing up the conformal coating which is there for a reason (and re-sealing it where necessary).

I accept that if the primary resistors keep on drifting then I am "in a hole" and should probably save my pennies for another one.

The problem is that the only source (that I know of) of used 720As in UK is either eBay or very occasionally a cal. lab. that is closing.   "Known good" isn't normally a term that applies to either.
 
Dave