Those are DC servos. All MX1 equipped machines are DC servos. AC servos do not have brushes. All Yasnac servos, whether DC or AC, are all black.
The color question comes with Fanuc equipped machines. Fanuc had all black when they were licensing servo designs from Gettys. Later when they introduced their own DC servos, the cap over the encoder was yellow. When their AC servos were released they changed the color to red.
Let's start with according to the information from the manual I uploaded terminals 5&6 are L1 & L2, as labeled on the terminals. I'm not tying those to the DC servo output, but I'll bet someone has. Terminals 7&8 are the outputs to the servo.
They don't say what leads there hooked to so I've no way to know what -8A to +9A meter swing means. I'll look for a more detailed description of the adjustment elsewhere.
For now I balanced the loads on the servo, till I know differently.