A & A Scales PT300 Service Manual - page 36

Summary of PT300

  • Page 1

    I pt300 service manual a & a scales 1-813-994-3190 fax 509-355-3498 www.Stainlessscales.Com.

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    Pt300, service manual rev b, october, 2000 1 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 standar...

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    Pt300, service manual rev b, october, 2000 2 table of contents scope of manual ......................................................................................................................................... 5 specifications .....................................................................

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    Pt300, service manual rev b, october, 2000 3 low batt indicator: ......................................................................................................................................23 power down shutoff: .................................................................................

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    Pt300, service manual rev b, october, 2000 4 table of illustrations f igure 1 b lock d iagram ................................................................................................. 8 f igure 2 b attery c harger .................................................................................

  • Page 6: Scope of Manual

    Pt300, service manual rev b, october, 2000 5 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 ...

  • Page 7: Specifications

    Pt300, service manual rev b, october, 2000 6 specifications electrical display settling time: 950 milliseconds to typical reading (static). Accuracy: ±1% of applied load ±1 display division in static mode ±2% of applied load ±1 display division in roll-over mode. Overcapacity: 105% of nominal capaci...

  • Page 8: Environmental

    Pt300, service manual rev b, october, 2000 7 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...

  • Page 9

    Pt300, service manual rev b, october, 2000 8 figure 1 block diagram power supply battery drivers low battery sensor on off lamp lb/kg zero hold/rel total/local print switches input buffer micro controller display serial output 12v serial input receiver loadcells summing board analog/digital input in...

  • Page 10: Theory of Operation

    Pt300, service manual rev b, october, 2000 9 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 i...

  • Page 11: Charger:

    Pt300, service manual rev b, october, 2000 10 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 ...

  • Page 12: Low Voltage Sensor:

    Pt300, service manual rev b, october, 2000 11 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 ...

  • Page 13: Analog Section:

    Pt300, service manual rev b, october, 2000 12 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 ...

  • Page 14

    Pt300, service manual rev b, october, 2000 13 auto zero integrate deintegrate u17 pin 1 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 ...

  • Page 15: Microprocessor Section:

    Pt300, service manual rev b, october, 2000 14 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...

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    Pt300, service manual rev b, october, 2000 15 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 le...

  • Page 17: Troubleshooting

    Pt300, service manual rev b, october, 2000 16 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 i...

  • Page 18: Scale Shuts Off.

    Pt300, service manual rev b, october, 2000 17 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 s...

  • Page 19: Batteries Won'T Charge.

    Pt300, service manual rev b, october, 2000 18 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 ch...

  • Page 20: Tests, Waveforms and

    Pt300, service manual rev b, october, 2000 19 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...

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    Pt300, service manual rev b, october, 2000 20 clk rd mi __ wr rfsh _____ 0038h rfsh see below see below 0ffh ? 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...

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    Pt300, service manual rev b, october, 2000 21 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 0.1ms/div a04 50ms/div a03 20ms/div a02 10ms/div a01 5ms/div a00 2ms/div figure 8 blank eeprom test, address lines.

  • Page 23: System Checkout Procedure

    Pt300, service manual rev b, october, 2000 22 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 sh...

  • Page 24: Amplifier:

    Pt300, service manual rev b, october, 2000 23 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 eviden...

  • Page 25: Sio (Totalizing):

    Pt300, service manual rev b, october, 2000 24 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 sl...

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    Pt300, service manual rev b, october, 2000 25 turn both scales off. Now put the scale under test in the slave position and the other scale in the master position, like this . . . Scale under test master leave any other cable disconnected figure 11 sio slave test turn both scales on. Wait until both ...

  • Page 27: Load Cells:

    Pt300, service manual rev b, october, 2000 26 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 strai...

  • Page 28: Procedures

    Pt300, service manual rev b, october, 2000 27 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 desig...

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    Pt300, service manual rev b, october, 2000 28 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 tor...

  • Page 30: Disassembly

    Pt300, service manual rev b, october, 2000 29 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. Sm...

  • Page 31: Remove and Replace Load Cell

    Pt300, service manual rev b, october, 2000 30 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 b...

  • Page 32: Assembly

    Pt300, service manual rev b, october, 2000 31 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 ...

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    Pt300, service manual rev b, october, 2000 32 1 2 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 surf...

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    Pt300, service manual rev b, october, 2000 33 the battery tube and the printed circuit board. 17) install tow board mounting screws. 18) check and adjust calibration as needed. 19) reassemble keyboard assembly 20) replace bezel screws.

  • Page 35: Unpacking and Installation

    Pt300, service manual rev b, october, 2000 34 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 a...

  • Page 36

    Pt300, service manual rev b, october, 2000 35 spare keypad. Main circuit board. Summing board. Load cells. Check straps. Charging transformer. Span resistors, 124 Ω , 174 Ω ..

  • Page 37: Connector Pinouts

    Pt300, service manual rev b, october, 2000 36 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...

  • Page 38: Pt300 Main Circuit Board

    Pt300, service manual rev b, october, 2000 37 pt300 main circuit board parts list pt300 circuit board reference: quantity: 1.22mhz crystal 1 liquid crystal display (lxd # 65r9f09kgj) ds1 1 led’s d9,d10,d11,d12, d13,d14,d15,d16 8 right angle post header amp #1-640457-0 1 28 pin dip socket amp #641561...

  • Page 39

    Pt300, service manual rev b, october, 2000 38 4.7k ohm ¼ w 5% r5,r31 2 10k ohm ¼ w 5% r6,r9,r10,r32 4 10k ohm ¼ w 1% r14 1 47k ohm ¼ w 5% r50 1 100k ohm sip, 8pin, #1 common rn1 1 150k ohm ¼ w 1% r25,r26 2 180k ohm ¼ w 5% r12 1 1m ohm ¼ w 5% r4 1 5m ohm ¼ w 5% r33 1 1n914 d2,d3,d18,d19 4 1n4001 d1,d...

  • Page 40

    Pt300, service manual rev b, october, 2000 39 pt300 summing circuit board parts list pt300 summing board rev. 1 reference: quantity: 14pin dual row, 90º, header 3m #2414-5222tg jp1 1 10k ohm trim pot r1,r2,r3,r4 4 47m ohm ¼ w 1% r6 1 15m ohm ¼ w 5% r8 1 22m ohm ¼ w 5% r7 1 500 ohm pot r5 1 header, 4...

  • Page 41: Appendix A

    Pt300, service manual rev b, october, 2000 40 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 i...

  • Page 42

    Pt300, service manual rev b, october, 2000 41 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...

  • Page 43

    Pt300, service manual rev b, october, 2000 42 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 revis...

  • Page 44: Schematics and Parts Layout

    Pt300, service manual rev b, october, 2000 43 schematics and parts layout number title pages 072391-102 pt300 schematic 3 none pt300 board assembly 1 none pt300 internal harness 1 none pt300 summing board 1 none scale interconnect cables 2 000196 pt300 assembly 1.

  • Page 45: Appendix B

    Pt300, service manual rev b, october, 2000 44 appendix b schematics.

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    Pt300, service manual rev b, october, 2000 45.

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    Pt300, service manual rev b, october, 2000 46.

  • Page 48: Totalizing Cable

    Pt300, service manual rev b, october, 2000 47 totalizing cable.

  • Page 49: Charging Cable

    Pt300, service manual rev b, october, 2000 48 charging cable.

  • Page 50

    Pt300, service manual rev b, october, 2000 49 loadcell and summing board.

  • Page 51: Internal Cable Assembly

    Pt300, service manual rev b, october, 2000 50 internal cable assembly.

  • Page 52: Parts

    Pt300, service manual rev b, october, 2000 51 parts.