I just retrieve an old Sansui Model 370 Turntable and have it clean it up. It was found to be working except the hummings. As such, I went further to check the output from the Pick-up Cartridge and not the followings:
1. Red and Green cable were connected to the the Centre and outer RCA/Audio cable. 2. Blue and White were connected to the the Centre and outer RCA/Audio cable.
Not too sure if this is the correct connections. The RCA/Audio cable is about 1.5 metre in length (maybe is may cause the humming). The RCA cable was connected to the Phono Input socket of the Image Audio Equalizer to boost up the signals from the Phono. The earth cable from the Phono was connected to the Power Amplifier which in turn was connected to the Green Earth Power Socket.
I am running out of ideas as to where the hummings still come from.
I don't know what the Image Audio Equalizer nor the Green Earth Power Socket actually are or do. But you have either a ground loop from too many potential ground points or you have no ground on the cartridge. It is unusual to "boost" the phono signal until after it is sent through a phono pre amplifier. Unless, that is, you are using a moving coil cartridge which requires a boost in overall voltage to drive the phono pre amp to adequate levels. Moving magnet cartridges should be input directly to the pre amplifier. Most equalizers should come after the pre amp or else be placed in the pre amp's tape or processor loop.
Whether your wiring scheme on the cartridge is correct is a matter of what the manufacturer instructs. From what you've said, you could still have the cartridge wired out of phase. Out of phase, however, will not result in a grounding problem. But, you could possibly have one channel not grounded properly which would cause a hum.
I would take the phono input to its simplest termination, directly into the phono section of your pre amp with the table/arm/cartridge grounded at the pre amp. Forgo any other connections until you have determined whether the cartridge is properly wired. Add one item at a time until you get your ground noise. That is the connection you will have to rectify.