KEPCO MBT Series - Manual (Page 120)

4-14
MBTSVC111609
the crowbar protection circuit which trips the main POWER circuit breaker, shutting off the MBT
Power Supply.
4.3.2 RELAY AND FLAGS BOARD A2 (See Schematic Diagram, Figure 6-19 for Models M, MG,
Figure 6-20 for Models MR, MGR)
The main function of this board is to deliver all the flags necessary for Digital Control Board A3.
On units with the "R" option installed, this board also contains the circuits which control the
opening and closing sequences of the output/polarity reversal relays. The principal circuits of
this board are as follows:
• ±15V D-C Regulators (U1, U2)
• Logic Flag Circuits (U3D, U4)
• Status LED Drivers (U3A, U3B, U3C, U3E)
• A-C Power Loss Circuit (LC1)
• Crowbar and Circuit Breaker Command Circuit (U3F, U4, U8A, LC3)
For MR and MGR Models the A2 board also incorporates the following additional circuits:
• Logic Circuit for Open/Close Command Sequencing (U5A, U5B, U5C, U5D, U8B, U8C,
U8D, U6A, U6B)
• Power Relay Drivers (K1, K2, CR3, CR4)
• Relays for switching the Sensing Leads (K3, K4)
This board differs between options of a particular model (as noted above), as well as between
models (due to a few components (decoupling capacitors between power and sensing leads).
The A2 board is connected to the A5 Mother Board via connector A2P1; two twisted-wire cables
connected to A2J1, A2J2, and A2J3, provide interconnections between the A2 board and Auxil-
iary Power Supply Board A4, terminal block A6TB1, and POWER circuit breaker A6CB1,
respectively. Jumper A2J5 permits circuit breaker A6CB1 to either trip upon detection of input
power loss (J5 installed) or not trip upon detection of power loss (J5 not installed).
(M, MG) Header A2J4 is incorporated on the A2 board for units without the “R” option. If the
jumper is installed between A2J4 pins 1 and 2, illumination of the front panel OUTPUT
ENABLED indicator is controlled by the software in response to the DC ON/DC OFF com-
mands. If the jumper is installed between A2J4 pins 2 and 3, the OUTPUT ENABLED indicator
is on and cannot be controlled by MBT software in response to DC ON/DC OFF commands.
4.3.3 DIGITAL CONTROL BOARD A3 (See Schematic Diagram, Figure 6-21)
The Digital Control Board A3 receives digital commands over the two-wire IEEE 1118 bus
(remote mode) or through connector J5 from the front panel controls (local mode). These com-
mands cause the A3 board to generate the two analog reference signals (voltage and current)
used by Analog Control Board A1 to control the output of the power supply. The analog signals
reflecting the output values are converted to digital signals for transmission to the external con-
troller via the IEEE 1118 bus. Digital Control Board A3 also controls Front Panel Board A8,
accepting the digital commands from the keypad and front panel VOLTAGE and CURRENT