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Power Supply Circuit Each distribution board contains its own power supply, a Two -Wire current loop (M, an RS422 interface, and eight dispenser loop drive circuits with auto -isolation. Both of the input interfaces provide opto-coupled isolation between the controller and the dispensers. The dispenser loop drive is configured in a star drive and operates from 12VDC at 45ma for dispensers and CRINDs or 20ma for G -CATs. Each board has two separate isolated power supply sections. One section is to provide voltage for the dis- penser loop drivers (and associated logic) while the other section provides the voltage to operate the RS422 inter- face. Each section uses a separate winding on the second- ary of the transformer. The dispenser loop drivers are powered from the filtered, but unregulated, 12VDC. The unregulated 12V may be between +9 and +15 VDC because of AC line variations. This unregulated 12VDC is also regulated down to +SVDC for the loop driver logic. There are three test points pro- vided: TWI +12 (unregulated +12VDC) TWI +5 (regulated +5VDC) TWI GND (reference) The RS -422 section is powered from the 10V secondary of the transformer. The unregulated 10V may be between +7 and +13VDC because of AC line variations. This voltage is rectified and filtered to provide the input current for the opto-couplers when the RS422 interface is used. This filtered voltage is also regulated down to the +5VDC for the RS422 driver. Once again, there are three test points provided: RS +10 (unregulated +1OVDC) RS +5 (regulated +5VDC) RS GND (reference) NOTE: These supplies are isolated. You MUST use the ground associated with the voltage test points to obtain meaningful readings. NOTE: If the distribution box has two distribution boards, you will need to check the test points on both boards to ensure that all required voltages are present. MDE-2714A • Universal Distribution Box Service Manual • 02196 Page 7