Advantest R6551 DMM

[radhaz]

Hi guys.
I have an Advantest R6551 DMM bought off of Ebay. It mostly works OK, but the AC functions are pretty much dead (ACI, ACV). Using my DMMCheck I get no response on ACV or ACI), DC stuff and ohms are good.
There is not a service manual to be found anywhere. Any ideas about where to begin looking? This DMM is from around the late 1980s early 1990s.

[rastro]

Advantest doesn't seem to have much information available on most of their test gear.

FWIW some principals of operation are in the back of the user manual.  http://exodus.poly.edu/~kurt/manuals/manuals/Other/ADV%20R6551,%20R6551EMC%20%20Operation.pdf

Since it's all A/C functionality not working you may want to look for a relay that routes the input's for the A/C path from the banana jacks.  Perhaps DC is the default path?

It might be worthwhile to post a few pictures of the insides.