Pace PRC 2000-2M User Manual

PRC 2000-2M SYSTEMS

PC BOARD TROUBLESHOOTING

HS 150 CALIBRATION PROCEDURE

SERVICE MANUAL ADDENDUM

MANUAL NO. 5050-0365

REV. B

INTRODUCTION

The following pages detail theory of operation and procedures for troubleshooting both the Microprocessor PCB and Multifunction PCB assemblies and calibration of the HS 150 system. The included pcb troubleshooting Flow Charts will assist the technician in determining the source of a malfunction down to circuit area or component level.

If you should encounter any difficulty in trouble shooting the pc boards or calibrating the HS 150, contact PACE Customer Service at TEL. (301) 490-9860, FAX (301) 604-9215.

MICROPROCESSOR PCB ASSEMBLY

THEORY OF OPERATION

GENERAL DESCRIPTION

The PACE part number 6020-0072 microcontroller (Microprocessor) board is the control for the Thermal Management Center section of the PRC2000 Repair center. The main purpose of the board is to measure and control the handpiece temperature established by the operator. Refer to schematic “Microprocessor PCB Assembly Schematic” in this manual or PACE drawing number 5000-0281.

POWER SUPPLY

The transformer secondary AC is rectified by the bridge rectifier and filters to +14 Vdc, and -14 Vdc and fed into the board of J5. The +14 Vdc is fed into regulator U1 that regulates the voltage down to +5 Vdc. The -14 Vdc is fed into regulator U2 which regulates it down to -5 Vdc.

ZERO CROSSOVER DETECTOR

Comparator U8D is used as a zero crossover detector. AC voltage from the transformer is rectified by diodes CR3 and CR4 to produce a rectified unfiltered voltage signal at U8D pin 11 (Fig 1 signal “A”). Signal “A” is compared with a reference voltage to produce a low going signal at the time period that the AC voltage is crossing zero volts (Fig 1 Signal “B”). Signal “B” at U8D pin 13 is the zero crossover signal that is used to enable the triggering circuits of the triacs at the zero crossover point.

Figure 1. Zero Crossover Detector

RESET, WATCHDOG, AND BROWNOUT CIRCUITS

Comparator U8B is used as the reset and brownout detector. When power is first turned on, the unregulated +14 Vdc charges C23 through R37 until voltage on C23 passes the 2 Vdc ref. voltage at U8B pin 6. The output of U8B (pin 1) will then go high and turn off Q4 which will remove the reset from the microcontroller. If the unregulated +14 Vdc falls below 6.8 Vdc the U8B will detect a brownout condition and continuously apply a reset to the microcontroller. Comparator U8A along with Q3 comprises the watchdog circuit. The microcontroller will supply a pulse stream out of U3 pin 17 if the program is executing properly. If the program fails, the pulse stream will stop pulsing Q3 on and allow C21 to discharge causing U8A output (pin 2) to go low and turn on Q4, resetting the microcontroller. When the reset is applied to the microcontroller, R3 provides a feedback into the watchdog circuit to turn on Q3 and release the reset so that the microcontroller may restart its program.

MICROPROCESSOR PCB ASSEMBLY

DISPLAY DRIVER

The LED display is multiplexed under software control. The power is supplied to the anodes for about 2.8 ms out of the 11.11 ms, from the driver transistors (Q13-Q16). The driver transistors are controlled from pin 36 through pin 39 of U3 (microcontroller). The information for the cathodes of the display is supplied through driver U5 and U6-10 with the current limited by RN5. Information to the cathode’s drivers is supplied from the microcontroller port 2 (U3 pin 21-28).

VACUUM PUMP DRIVER

The vacuum pump driver is comprised of transistors Q1 and Q17 which are controlled from both the microcontroller (U3 pin 13) and the handpiece switches. When a switch is activated low, base current will flow through Q1 base and R13. Q1 will turn on which in turn will turn on Q17 applying power to the motor of the pump. At the same time the voltage at U3 pin 13 will go low, letting the program know that a switch has been activated. The program will let the motor run at +28 Vdc for 150 ms and then it will start chopping the voltage at a 2KHz rate by bringing pin 13 low and cutting off the base voltage of Q1. When the switch is released the microcontroller will read pin 13 between chops (to see if the pin is not being held low by the switch) if pin 13 is high, the microcontroller will reset the pump state to off (pin 13 held high). Although Q1 may fail if the handpiece shorts and AC voltage is fed into the switch input, the zener diode CR8 will protect the microcontroller.

BUZZER

U8C comparator forms a 2.05KHz square wave oscillator that drives Q21, which in turn drives the audio transducer (LS1) at its resonant frequency. The driver is controlled by the microcontroller (U3 pin 11) holding the base of Q21 low to turn it off. The RESET will also hold the driver transistor (Q21) off through CR5.

TRIAC DRIVER

Output to the triac drivers takes place on the back edge of the fourth digit display signal. Before turning off the digit four display, the data on port two of the microcontroller is changed to the triac data and then turns digit four off (signal going high), which clocks the triac data into U7. U7 is an eight bit latch that holds the triac information. The output of the latch is enabled with the zero crossover signal which allows any output that has a high latch within to turn on the associated triac. The microcontroller (U3) output from pin 10 will allow the microcontroller to turn off all triacs at once through CR1. The high signals from U7 drive inverter U6 to turn on the transistors that drive the current into the gates of the triacs. Each power triac driver has two drive transistors to allow the triacs to be triggered from a negative voltage, so that the trigger will be in quadrant two, and quadrant three. R11 is in series with the auxiliary triacs to limit the output current if a handpiece is plugged into the auxiliary outputs.

MICROPROCESSOR PCB ASSEMBLY

RTD CONSTANT CURRENT SOURCE AND CHANNEL MULTIPLEXOR

U9A makes up a constant current source that provides the current excitation for the RTD (in the connected handpiece). The current is multiplexed to one of six RTDs to be measured. U9B amplifier feeds back the RTD voltage to modify the constant current source to correct for the non-linearity of the RTD. U11 is a dual eight channel multiplexor under control from the microcontroller (Mux A - Mux C signals). The multiplexor will switch the constant current source to each of the RTDs and switch the RTDs voltage up to the analog to digital converter (U10). CR9 and CR10 are in series with the multiplexor power inputs so that if the heater voltage feeds back onto the RTD input, the voltage will be fed through the input diodes of the multiplexor; and the power rail will float up to the input voltage and protect the chip (U11) from damage. Channel seven and eight of the multiplexor switch in the two very high precision calibration resistors every four minutes to allow the microcontroller to dynamically re-calibrate the RTD measuring circuits. R48 is the low calibration resistor (32°F), and R50 is the high calibration resistor (987°F).

ANALOG TO DIGITAL CONVERTER

U10 is a dual-slope-integrating analog to digital converter front end. Under control from the microcontroller (ADC A and ADC B signals), the dual-slope-converter will integrate the input for 16.6 ms into C25 and time the deintegration to the reference voltage. The microcontroller will then use the two times, and the reference voltage, to calculate the temperature of the RTD.

KEYBOARD INPUTS

The microcontroller (U3) drives the keyboard directly by providing the row drive (low signal) to the keyboard out of pin 1 and pin 2. After a row has been selected, the microcontroller will read the keyboard data from pins 3, 4, and 5.

EEPROM MEMORY

U4 is a 1024 bit Serial Electrically Erasable Programmable Memory. The microcontroller (U3) interfaces with the memory through a serial interface using U3 pin 14 to select the memory chip, U3 pin 15 to clock the data into the chip, and pin 16 to supply and read the data.

MICROPROCESSOR PCB ASSEMBLY

ERROR CODES

There are certain error codes that may show up on the Digital Readout (display), if the program detect a fault within the system. These Digital Readout errors are listed below with the probable cause (fault) and the probable repair solution.

1. “ E “ in the middle of the Digital Readout. This error indicates an error on power-up when the system program is checking the Random Access Memory or when comparing the sum-check against the store sum-check. The microcontroller (U3) will require replacement.

2. “E-1” on the Digital Readout. This error indicates that the system program has detected a high resistance on the sensor input (RTD open). Check the handpiece, J1 connector, RTD Constant current source, channel multiplexor, and Analog to Digital converter.

3. “E-2” on the Digital Readout. This error indicates that the system program has detected a low resistance on the sensor input (RTD shorted). Check the handpiece, J1 connector, RTD Constant current source, channel multiplexor, and Analog to Digital converter.

4. “E-3” on the Digital Readout. This error indicates that the system program has detected an RTD resistance on the sensor input greater then the referenced resistance for 1000°F, but less then the resistance required to cause an “E-1” error (Digital Readout overflow). Check the handpiece, J1 connector, RTD Constant current source, channel multiplexor, and Analog to Digital converter.

5. “E-4” on the Digital Readout. This error indicates that the system program has detected an RTD resistance on the sensor input lower than the referenced resistance for 32°F, but higher than the resistance required to cause an “E-2” error (Digital Readout underflow). Check the handpiece, J1 connector, RTD Constant current source, channel multiplexor, and Analog to Digital converter.

6. “E-5” on the Digital Readout. This error indicates an incorrect resistance for the calibration resistors (R48 and R50). Check the calibration resistors R48 and R50, RTD Constant current source, channel multiplexor, and Analog to Digital converter.

FLOW CHARTS

The following Flow Charts should be used to determine the source of the Microprocessor board malfunction down to a circuit area or component level.