Confirmation needed!

[Boatcarpenter]

Can anyone confirm that input pins A and B are positive and C and D are negative on an MX-7777?
Can't download the TM that has a schematic from LOGSA.

 

[cranetruck]

Don't have a schematic handy, but the unit is internally grounded to the case, so an ohm meter should do the trick, just check continuity.
Or, take the cover off and look at the wiring....