BC-3500 Series - Rowe International

Section 4: Troubleshooting
With Q9 ON, the RAM chip select form U12A Pin 3 is allowed to pass through Q9 and be applied to the RAM U10
Pin 20. When Q9 is ON, it effectively becomes transparent.
With Q17 ON, the base of Q15 is pulled down, turning on Q15. When Q15 is ON, the +5-volt supply is applied
to the RAM U10 Pins 26 and 28 through Q15, relieving the battery.
With Q18 ON, voltage is applied to R157, providing a pull up for Q20. In this case, U20 Pin 30 through Q19 is
the controlling factor. When U20 Pin 30 is HIGH, Q19 is turned ON, which keeps Q20 OFF, which in turn keeps
Q13 and the switched 12-volt supply OFF. When U20 Pin 30 is LOW, Q19 turns OFF, allowing Q20 to turn ON
through the pull up R157. This turns ON Q13 and the switched 12-volt supply.
I/O PORTS
U8 is an input buffer decoded by U13 at address C200 hex. This port reads the PROGRAMMING/NORMAL mode
switch, all pushbutton switches, and the machine code information. When the processor reads memory locations
C200, the information on the switches will be brought into the processor.
U19 is an input buffer decoded by U13 at address C600. This port reads the TEST switches, coin switches, and
dispenser coin detectors. When the processor reads memory location C600, the information on these devices will
be brought into the processor.
U5 is and output latch decoded by U13 at address C100 hex. U5 controls the hopper motors, the stacker, and coin
lockout coil. The interface circuits for these functions are contained on sheet 3.
U16 is an RS485 interface chip allowing communication to test equipment and the Rowe BC programming aid.
U15 is an EPROM used to store information that must be kept, even if the battery voltage to the RAM dies. Original
date of manufacture, programming information, and other things are stored in the EPROM.
Sheet 2: Digital Display Driver
DS1 is the vacuum fluorescent display. It normally requires a negative supply voltage to operate. The bill changer
does not provide a negative supply, so the display tube and the display driver chip U1 are both "floating", that is, they
do not have a direct ground reference. This effectively simulates a negative supply.
R17 through R22 provide level shifting of the display clock, data, and reset control lines. Each pair of resistors sets
up a voltage divider, allowing the digital input signals on U14 to be level shifted to the voltages needed by U1.
When investigating this area, verify the proper voltages developed by the zener diodes. Referencing all measurements
to ground, U1 Pin 1 should be +30 VDC, U1 Pin 18 should be +14 VDC, DS1 Pin 1 should be +6.2 VDC, and
DS1 Pin 34 should be +11.8 VDC. Voltages on U1 Pins 20, 21, and 22 should swing between +30 VDC and +20
VDC.
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