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PT300, Service Manual Rev B, October, 2000 SAFETY SUMMARY The following general safety precautions must be observed during all phases of operation, service, and repair of this scale. Failure to comply with these precautions or with specific warnings elsewhere in this manual violates safety standards of design, manufacture, and intended use of the scale. Intercomp assumes no liability for the customer's failure to comply with these requirements. DO NOT OPERATE IN AN EXPLOSIVE ATMOSPHERE.
PT300, Service Manual Rev B, October, 2000 Table of Contents SCOPE OF MANUAL ......................................................................................................................................... 5 SPECIFICATIONS.............................................................................................................................................. 6 ELECTRICAL.............................................................................................................................
PT300, Service Manual Rev B, October, 2000 Low batt indicator: ......................................................................................................................................23 Power down shutoff: ....................................................................................................................................23 SIO (totalizing):...........................................................................................................................................
PT300, Service Manual Rev B, October, 2000 Table of Illustrations FIGURE 1 BLOCK DIAGRAM ................................................................................................. 8 FIGURE 2 BATTERY CHARGER ............................................................................................ 9 FIGURE 3 SWITCH ............................................................................................................ 10 FIGURE 4 INTEGRATOR/COMPARITOR ...........................................
PT300, Service Manual Rev B, October, 2000 Scope of manual This service manual describes the Intercomp PT300 scale specifications, theory of operation, interconnection, calibration, and servicing. Please refer to the users manual for detailed operating procedures and application information. This manual is separated into several sections, each containing information on a different aspect of the scale. The specifications show the design parameters for the scale.
PT300, Service Manual Rev B, October, 2000 Specifications Electrical Display settling time: Accuracy: Overcapacity: Safe Overload: Batteries: Battery Life: Battery Duration: Automatic Shutoff: Charging Voltage: Charging Current: Charging Time: Low Batt.: Fuse: 950 milliseconds to typical reading (static). ±1% of applied load ±1 display division in static mode ±2% of applied load ±1 display division in roll-over mode. 105% of nominal capacity. 150% of capacity. 6 x 1.2 volt AA nickel cadmium cells.
PT300, Service Manual Rev B, October, 2000 All metal case provides EMI/RFI immunity. Caution The scale and connecting cables should be operated at a minimum distance of 3 feet (1 meter) from any transmitting apparatus and least 10 feet (3.3 meters) from a radiating antenna. Environmental Operating Temperature: Humidity -20 to 150º F (-28 to 65º C). 10 to 95% Non-Condensing.
PT300, Service Manual Rev B, October, 2000 12v Power Supply On Off Lamp Lb/Kg Zero Hold/Rel Total/Local Print Switches Battery Input Buffer Micro Controller Low Battery Sensor Drivers Display Connector Input Connector Serial Input Receiver Serial Output Output Loadcells Summing Board Analog/Digital Input Figure 1 Block Diagram 8
PT300, Service Manual Rev B, October, 2000 Theory of Operation For the following discussion, please refer to the schematics in appendix B. Power supply: The power supply section provides a source of ±5 volts, a nickel-cadmium battery charger, and the detector for low battery condition. The input is designed to accept any voltage between 10.5 and 14.6 volts. +14.6v-+10.5v Current C h a rge L i m itin g Sensor Constant Resistor Current R20 S o u rce Q5 10.0v D4 D20 9.3v D5 S w itch 8.
PT300, Service Manual Rev B, October, 2000 Charger: The battery charger works on the constant voltage charging principle. The diode D4 is a 10 volt zener diode. This diode is biased by the constant current source formed by R1, R2, Q8, D2, and D3. Current is sourced to D4 until the voltage across R2 is equal to the voltage dropped across D2. D3 cancels the voltage drop across the Vbe of Q8. R1 is used to draw a bias current through D2 and D3. Q7 is configured as a common base amplifier, with 9.
PT300, Service Manual Rev B, October, 2000 Low Voltage Sensor: R9, D7, and Q2 work much the same as R6, D6 and Q5 in the power switch section. The addition of D8 causes Q2 to switch 0.3 volts before Q5. In practical terms, Q2 will be biased on until the switched voltage drops to 7.2 volts. Below this voltage the low voltage sense line goes high. R10 provides a path for any leakage current through D7 and D8. Regulator: Q3 a standard 3 terminal regulator in a TO-92 package.
PT300, Service Manual Rev B, October, 2000 Analog Section: The analog section takes the signal from the load cells (about 10 mV) and translates this signal into a digital representation. In our case this representation is a sixteen bit number in a counter register. Instrumentation Amplifier: The signal from the load cells is about 10 mV at full load. U18 takes this signal and amplifies it for use by the A/D converter.
PT300, Service Manual Rev B, October, 2000 Integrate Deintegrate U17 Pin 1 Auto Zero Auto Zero Figure 5 Conversion Cycle Let’s examine the operation of the converter. Start with C7 at zero volts. The +input voltage charges C7 for a fixed period called Time-integrate. Then the integrator input is switched to the reference voltage and C7 is discharged for an amount of time called Time-deintegrate; this time is related to the input voltage.
PT300, Service Manual Rev B, October, 2000 Now for the messy details of implementation; U17 is driven through the integrate, deintegrate, and auto-zero cycles by a counter U12. This counter is loaded by the micro processor to start the cycle, and U12 pin 6 output is used as an interrupt to signal that the conversion is over. The counter's clock is driven by ones output from the Counter-Timer-Chip, U13.
PT300, Service Manual Rev B, October, 2000 Display Driver: Any LCD display must be driven by a waveform with a net zero DC voltage. If the driving voltage has any DC component the display will be destroyed. A display driver chip (U10) provides the correct drive for 4 of the display digits. The leading 100000's digit, the trailing 0/5 digit and all annunciators are driven by U6, U7, and U8. U6 latches most of the desired segment drive information. One line of U6 drives the serial output circuitry.
PT300, Service Manual Rev B, October, 2000 Troubleshooting Caution Changing some parts may cause a large change in calibration whereas others may or may not change the calibration, depending on the nature of the problem. The most sensitive parts are in the analog and power supply sections; this includes Q3, U17, U18, U19, and their related resistors and capacitors. The areas that normally would have no effect are: CPU, display and driver, memory chips, and serial interface sections.
PT300, Service Manual Rev B, October, 2000 Scale shuts off. Normally the scale shuts itself off after a long period of inactivity. The length of time is defined at the time the scale is configured, but is normally one hour. If the microprocessor is acting up, one of the symptoms may be that the scale shuts off after the A/D is initialized and starts to run. All this tells up is that the microprocessor is not resetting the counter U12, so its reaching MIN/MAX count.
PT300, Service Manual Rev B, October, 2000 Low batt indicator won't turn off. It is possible that the output from the batteries is really low. Look at the cells and charger circuit for these problems. The low voltage sensor could be out. The driver for the display could be bad. Batteries won't charge. The most common problem is the Fuse, start there. Check for bad batteries. The charger circuit could be out. Check for bad connections or a defective charging cable.
PT300, Service Manual Rev B, October, 2000 Tests, Waveforms and Voltage measurements Blank EPROM test. One of the most challenging problems is finding a problem in the "microprocessor kernel," that is, the RAM, ROM, microprocessor and related circuitry. The hardest part is that everything is tied together, and if you cut it apart, nothing works. The best way to tackle this problem is to run a VERY simple test program. This allows you to determine that the microprocessor is working first.
PT300, Service Manual Rev B, October, 2000 CLK RD WR __ MI _____ RFSH 0038h RFSH 0FFh See Below ? See Below 039h 00h Figure 7 Blank EEPROM Test Waveforms For the first three clock pulses the Z80 reads 0FFH from location 038H. As part of an instruction fetch the Z80 does a memory refresh cycle. We do not use this for anything, but its there. Then the Z80 writes out the address 0039 on the stack. Note that this takes two write cycles.
PT300, Service Manual Rev B, October, 2000 A15 20mS/Div A14 10mS/Div A13 5mS/Div A12 2mS/Div A11 1mS/Div A10 0.5 mS/Div A09 0.1mS/Div A08 50mS/Div A07 0.1mS/Div A06 0.1mS/Div A05 0.
PT300, Service Manual Rev B, October, 2000 System checkout procedure The following measurements are typical values. When tolerances are given the signal must fall within the given ranges. Special measuring conditions will be specified as needed. The measurements are given in the order that you should use them. Condition: Scale is off and plugged into the charger. No cells installed. A variable power supply connected to the power supply leads, set to 12.0V. Charger voltage: Positive battery lead, 8.
PT300, Service Manual Rev B, October, 2000 If the display backplane drive is missing, TURN THE SCALE OFF IMMEDIATELY. Operation without a backplane signal will damage the display quickly. Remove the display while determining the cause of the missing backplane signal. Display damage will be evident as display segments that are on permanently, even with the scale off. Amplifier: No load on scale, or a load cell simulator set to 0.05 mV/V. U18, Pin 11, zero input = 0.05 volts.
PT300, Service Manual Rev B, October, 2000 SIO (totalizing): To test the totalizing function you will need 2 scales (one is the scale under test) and a totalizing cable. Put the scale under test into the master position, and the other scale in the second position on the cable. Scale under test Slave Leave any other cable Disconnected Figure 10 SIO Master Test Turn both scales on. Wait until both scale go to a stable zero display.
PT300, Service Manual Rev B, October, 2000 Turn both scales off. Now put the scale under test in the slave position and the other scale in the master position, like this . . . Master Scale under test Leave any other cable Disconnected Figure 11 SIO Slave Test Turn both scales on. Wait until both scale go to a stable zero display. Insure that both scales are in the totalizing mode, look for the bar next to TOT on the display. Press the local/total key to turn on the bar if needed.
PT300, Service Manual Rev B, October, 2000 Load Cells: Each PT300 scale has two load cells. These load cells are the transducers that convert mechanical energy (weight) to electrical energy. Each load cell has 4 strain gages (1000 ohms each) and a temperature compensation resistor. The four strain gages are wired together to form a Wheatstone bridge. Color coding of the wires.
PT300, Service Manual Rev B, October, 2000 Procedures Please see Parts section for the parts drawing. Loading pads & blocks. At several points in the following procedures you will be asked to use loading blocks. The tip of a test press may exert 20000 pounds of force. While PT300 scales are designed to accept this force, they may not tolerate this on a single point. You must use a block to distribute the force over the load surface.
PT300, Service Manual Rev B, October, 2000 11) Apply 5000, 10000, 15000, and 19000 lbs and verify span is within 1.0% of applied load. Make any adjustments necessary to bring the unit into tolerance. Insure that unit does not indicate overcapacity before 20000 lbs of applied weight. 12) Apply Torx-seal to lock the potentiometer shaft. 13) Reassemble keyboard assembly. 14) Replace bezel screws.
PT300, Service Manual Rev B, October, 2000 Remove and replace main circuit board Tools required Twenty thousand pound calibration press. 8" x 8" x 2 ± .25” aluminum loading block. 8" x 8" x 0.5" rubber loading pad. Static dissipation station. #2 Phillips screwdriver for bezel and board mounts. Small slotted blade screwdriver. Torque-seal potentiometer shaft sealer. Caution: The following procedure must only be performed at a static controlled workstation.
PT300, Service Manual Rev B, October, 2000 Remove and replace load cell Tools required Twenty thousand pound calibration press. 8" x 8" x 2 ± .25” aluminum loading block. 8" x 8" x 0.5" rubber loading pad. Static dissipation station for any P.C. board work. #2 Phillips screwdriver for bezel and board mounts. Torque wrench covering 12 ft-lbs. Torx T30 bit. Small slotted blade screwdriver. Locktite 242 removable Threadlocker (BLUE). Torque-seal potentiometer shaft sealer.
PT300, Service Manual Rev B, October, 2000 Assembly 16) Set new load cell in place. 17) Glue the load cell lead off to the side so it doesn’t run under the middle of the load cells. 18) Thread load cell lead through hole in case. 19) Apply RTV liberally where load cell lead enters case. Work RTV compound inside feed-through hole. 20) Replace strap assembly. 21) Replace 8 bolts holding strap assembly. Use permanent locktite (RED) and torque bolts to 12 ft-lbs. 22) Replace platform.
PT300, Service Manual Rev B, October, 2000 2 1 Figure 13 Load Cell Placement 1) Remove all 10 bezel screws. 2) Detach keyboard assembly and set aside. Do not unplug keyboard. 3) Remove 2 screws holding circuit board. 4) Remove main circuit from housing. Do not set the board on any conductive surface, including the scale. 5) Rotate summing board until potentiometer is accessible. 6) Turn scale ON. 7) Wait for scale to warm up. 8) Zero the scale.
PT300, Service Manual Rev B, October, 2000 the battery tube and the printed circuit board. 17) Install tow board mounting screws. 18) Check and adjust calibration as needed.
PT300, Service Manual Rev B, October, 2000 Unpacking and Installation Caution: Keep all packing materials in case scale must be shipped again. If the packing material are lost or damaged, contact the service department for a replacement shipping carton. Units shipped in any other materials will automatically void the warranty. Use of a load cell simulator During circuit board checkout it may be awkward to apply 20000 pounds to develop internal signals.
PT300, Service Manual Rev B, October, 2000 Spare keypad. Main circuit board. Summing board. Load Cells. Check straps. Charging transformer. Span resistors, 124Ω , 174Ω .
PT300, Service Manual Rev B, October, 2000 Connector pinouts A: +5V B: - Input C: Ground D: - Output E: +12V (Charging Voltage) F: + Input G: Unused H: + Output Transmit Data format M Kg Format = A_O_-XXXXXXX._Lb Z Format explanation: A = Scale code (Signifies the scale, could be A for scale A, B for scale B etc..) Space M,O,Z = Error code M = motion, O = overcapacity, Z = zero, space = no error Space Minus sign if negative, space if positive.
PT300, Service Manual Rev B, October, 2000 PT300 Main Circuit Board Parts List PT300 Circuit Board 1.22Mhz Crystal Liquid Crystal Display (LXD # 65R9F09KGJ) LED’s Right Angle Post Header AMP #1-640457-0 28 pin DIP Socket AMP #6415615-3 Display Stand Offs Samtec #ECC-117-TT/03 Fuse Clips DIGI KLIP #MC-27 6 pin Dual Row Header Posts 3M #2406-6122 Fuse, Buss type AGC-1 5pF Ceramic Disc, 50v Radial Leads .01uF Ceramic Disc, 50v Radial Leads 0.1uF Polypropylene, 100v Axial Leads 0.
PT300, Service Manual Rev B, October, 2000 4.
PT300, Service Manual Rev B, October, 2000 PT300 SUMMING CIRCUIT BOARD PARTS LIST PT300 Summing Board Rev.
PT300, Service Manual Rev B, October, 2000 Appendix A Setting the deadload. The output signal from the load cells is set to a value slightly above zero with zero weight applied. This is done for two reasons; one is to detect any errors in the load cells, the other is to run the A/D converter in its most accurate operating point. The "Deadload" or "Tare" must be set with no weight on the scale.
PT300, Service Manual Rev B, October, 2000 1) It is assumed that the scale is disassembled with the main circuit board removed from the case (but still plugged in) and sitting on an insulating surface. The keypad must be plugged into the main circuit board. 2) On the keypad, press the Local/Total and the lb/kg and while holding them down turn the scale on and release all switches.
PT300, Service Manual Rev B, October, 2000 Selecting the Initial Span Range. It may be necessary to change the span resistor if you run out of travel when setting scale span. Likewise the span resistor may have to be changed when new circuit boards or load cells are installed. There are two revision boards; 300B and 300C. With the 300B board the span resistor (R24) must be unsoldered to change values. The 300C board has a shorting plug selecting a span resistor (R24, R52 or R53).
PT300, Service Manual Rev B, October, 2000 Schematics and Parts layout Number 072391-102 None None None None 000196 Title PT300 Schematic PT300 Board Assembly PT300 Internal harness PT300 Summing Board Scale Interconnect Cables PT300 Assembly Pages 3 1 1 1 2 1 43
PT300, Service Manual Rev B, October, 2000 Appendix B Schematics 44
PT300, Service Manual Rev B, October, 2000 45
PT300, Service Manual Rev B, October, 2000 46
PT300, Service Manual Rev B, October, 2000 Totalizing cable 47
PT300, Service Manual Rev B, October, 2000 Charging Cable 48
PT300, Service Manual Rev B, October, 2000 Loadcell and Summing Board 49
PT300, Service Manual Rev B, October, 2000 Internal Cable Assembly 50
PT300, Service Manual Rev B, October, 2000 Parts 51
