Started working through the DM502 assortment today. Though all were sold as "working" (of course), all but one fail at least one functional test (of course). All have different origins, though two had Tektronix stickers on them.
First thing I noticed doing the physical check: three of the units had an oversized slow blow fuse in the current measurement line.
The manual calls for a 2.5A fast blow fuse. Oddly enough, the current measurement function on these units isn't working. The fuse was blown on the fourth unit and when replaced, that function worked.
So I have one to put through the normal calibration and test procedure and three that are varying degrees of busted. The good news: these are pretty easy to diagnose and there aren't any really special parts. For fun, I am going to try and do this project without using anything exotic other than the low voltage calibration source.