KEPCO MBT Series - Manual (Page 123)

MBTSVC111609
4-17
The pass element transistors and associated circuits are electrically connected to two printed
circuit board subassemblies; the transistors are also physically mounted on the heat sink for
heat dissipation (see Figure 6-8). Low voltage model heat sink assemblies are interconnected
with chassis-mounted components, Mother Board A5, and Sensing Resistor and Crowbar
assembly A10 by means of one 9-pin connector on printed circuit subassembly A7A1. High volt-
age models use two 12- pin connectors, one on each printed circuit board subassembly, to inter-
connect the two subassemblies, the chassis-mounted components, Mother Board A5, and
assembly A10. High current models (MBT 6-32M and 15-20M) use a heavy duty cable mounted
between the two printed circuit board subassemblies to deliver the pass element output to the
Sensing Resistor and Crowbar assembly A10.
4.3.8 FRONT PANEL BOARD A8 (See Schematic Diagram, Figures 6-24)
Front Panel Board A8, Alphanumeric Display (LCD) A11 and Keypad A12 provide an interface
between the operator and the MBT power supply. Operator inputs from the keypad and from the
VOLTAGE and CURRENT optical encoders is sent to Digital Control Board A3 in order to initiate
a program or modify a value; display information from Digital Control Board A3 is sent to LCD
A11 by the Front Panel Board A8. Front panel board A8 is identical for all MBT models and
options, and contains the following circuits:
• VOLTAGE and CURRENT controls (optical encoders) and interface circuits (U5, U4, U2,
U3, U1C)
• Buffers (for “beeper” device and REMOTE status LED) (U1B, U1A)
• Status LEDs (DS1 through DS5)
• “G” Option selector switch (S1)
Transition type connector A8J1 connects the front panel board to Digital Control Board A3 via a
26-conductor flat cable (see Figure 6-11 for component locations). Connector A8J6 intercon-
nects Front Panel Board A8 with Mother Board A5 via a 9-pin flat cable. Connector A8J4 inter-
connects Front Panel Board A8 with the keypad via a 10-conductor flat cable. Alphanumeric
display A11 is plugged directly into connector A8J5.
Connector A8J7 provides the backlight diode voltage for LCD A11 via a twisted pair; however,
on some models this connector is not used: the backlight voltage is provided directly to the LCD
via connector A8J5.
Potentiometer R7, accessible through the top cover (see Figure 2-2), adjusts the contrast of
LCD A11.
The status indicator LEDs, DS1 through DS5 are visible from the front panel to display status:
VOLTAGE MODE, CURRENT MODE, POLARITY REVERSED, REMOTE, and OUTPUT
ENABLED, respectively. Indicators DS1 through DS4 are driven by signals from Relay and
Flags Board A2 via Mother Board A5; indicator DS5 is driven directly by Digital Control Board
A3, buffered by U1A.
Operation of the VOLTAGE and CURRENT control optical encoders is identical. Rotating VOLT-
AGE control in either direction produces clock pulses which trigger D-type flip-flops U3A and
U3B. U3B is always triggered set, indicating to Digital Control Board A3 that voltage is to be
decremented or incremented. Flip-flop U3A is either set or reset, indicating to Digital Control
Board A3 that voltage is to be incremented (clockwise rotation) or decremented (counterclock-