If you would like to perfect your CD74 further, measure the ripple frequency on the +- supply for the 12 volt regulators (supply for audio op-amps). You will find that your frequency measurement will be 50Hz when it is meant to be 100Hz right? After all it's going through a full wave bridge rectifier? Well, this is where Marantz assembly have stuffed up and it's an easy fix. If you check the service manual the schematic is drawn correctly from the transformer to the bridge rectifier but in practice has been implemented wrong where the result is only half wave rectification! This is because they have wired the transformer windings in reverse on the pcb power plug that forms the centre tap 0v. All that needs to be done is to reverse the green and blue wires on the pcb power plug and you will have doubled the effectiveness of the filter caps. So far, I have found every 74 & 84 wired this wrong way. All the best👍🏻 DK
If you would like to perfect your CD74 further, measure the ripple frequency on the +- supply for the 12 volt regulators (supply for audio op-amps). You will find that your frequency measurement will be 50Hz when it is meant to be 100Hz right? After all it's going through a full wave bridge rectifier?
Well, this is where Marantz assembly have stuffed up and it's an easy fix. If you check the service manual the schematic is drawn correctly from the transformer to the bridge rectifier but in practice has been implemented wrong where the result is only half wave rectification! This is because they have wired the transformer windings in reverse on the pcb power plug that forms the centre tap 0v. All that needs to be done is to reverse the green and blue wires on the pcb power plug and you will have doubled the effectiveness of the filter caps.
So far, I have found every 74 & 84 wired this wrong way.
All the best👍🏻
DK
Good to know that, thanks ! I'll check when I'll service my Marantz cd 74 ;)
Мне нравится этот аппарат!👍