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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 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, 8.6V
To check out the charger circuit, install cells.
Positive battery lead, 5.4V to 8.6V, depending on batteries state of charge.

On / Off switch:

Press the ON switch,
Q6, collector, 6.8V or greater.
Press the OFF switch.
Q6, collector, 0.7V or less.
Press the ON switch for the following tests.

Power Supplies:

U19, Pin 8 = 5.0V ±0.25V
U19, Pin 5 = -4.9V ±0.25V

U10 pin 5, 0.5mS/Div

U2 pin26, 5mS/Div

U3 pin 4, 0.2mS/Div

Figure 9 Test Waveforms

All signal measured with vertical gain set to 1 volt/division.  For the reset pulse, ground
and release the reset pin while watching with the oscilloscope.

CAUTION:

Summary of Contents for PT300

Page 1: ...I PT300 Service Manual A A Scales 1 813 994 3190 Fax 509 355 3498 www stainlessscales com...

Page 2: ...d maintenance of the equipment described herein While every precaution has been taken in the preparation of this manual Intercomp Corporation assumes no responsibility for damages resulting from the u...

Page 3: ...elector 14 Switches Reader 14 Display Driver 15 Serial IN OUT 15 TROUBLESHOOTING 16 SYMPTOMS 16 No power up nothing on display 16 Power up to random display 16 Power up to test pattern 16 Scale shuts...

Page 4: ...ELL 30 Disassembly 30 Assembly 31 CHECK FRONT BACK LOAD CELL BALANCE 31 UNPACKING AND INSTALLATION 34 USE OF A LOAD CELL SIMULATOR 34 COMPLETE LIST OF REQUIRED TOOLS AND MATERIALS 34 Spare parts list...

Page 5: ...E 4 INTEGRATOR COMPARITOR 12 FIGURE 5 CONVERSION CYCLE 13 FIGURE 6 LCD DRIVE 15 FIGURE 7 BLANK EEPROM TEST WAVEFORMS 20 FIGURE 8 BLANK EEPROM TEST ADDRESS LINES 21 FIGURE 9 TEST WAVEFORMS 22 FIGURE 10...

Page 6: ...ction section shows the way two or more scales work together to form a larger system The assembly instructions show correct assembly and disassembly techniques This manual is not designed to be a subs...

Page 7: ...re the scale shuts itself off Automatic Shutoff The scale turns itself off when the battery voltage gets down to approximately 6 3 volts Charging Voltage 11 5 volts 14 5 volts DC Protection is provide...

Page 8: ...ing Temperature 20 to 150 F 28 to 65 C Humidity 10 to 95 Non Condensing Calibration All scales are calibrated at the factory a fine span adjustment can be made using the potentiometer on the PT300 cir...

Page 9: ...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 Summ...

Page 10: ...r for low battery condition The input is designed to accept any voltage between 10 5 and 14 6 volts Q 5 D 4 D 5 D 2 0 C o n s t a n t C u r r e n t S o u rce C u r r e n t Lim itin g R e s i s t o r C...

Page 11: ...dicator circuit senses the current through R3 When 0 7 volts is developed about 28 milliAmps across R3 Q10 turns on lighting D20 R4 R R6 D6 Q9 Q5 Off On Logic Auto Off V Bat V Switched Gnd Gnd Gnd Fig...

Page 12: ...ill 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 stan...

Page 13: ...the gain of the amplifier Some of the amplifier s built in resistors are used to increase the gain stability hence the busy connections between U18 and the gain selection resistors R24 and potentiomet...

Page 14: ...rence voltage does not change so the rate of discharge should be a certain number of volts per second The higher the input voltage the higher the voltage that will be driven onto the integrating capac...

Page 15: ...N MAX bit out of counter U12 is used as the auto off signal To turn the scale off the computer does not service the end of conversion interrupt This also acts as a dandy watchdog timer if the micro is...

Page 16: ...n Figure 6 LCD Drive Serial IN OUT U15 Reads a 20 mA current loop and converts this to an opto isolated TTL signal across R31 R29 and R30 act as a voltage divider to limit the current through the curr...

Page 17: ...power but it might be eaten up with a shorted circuit board or filter capacitors Power up to random display We know that some power is reaching the display driver circuit but the microprocessor is not...

Page 18: ...r connector may be bad U4 may be defective Bad weights First check weighing technique Are the scales being used by a new operator Are the scales being used on level ground Are the operators using dumm...

Page 19: ...scale you need to look at the serial transmitter and receiver sections Look for the clock running at the wrong speed Try pressing the print button this should send the local weight down to the next sc...

Page 20: ...you to find any remaining problems On a Z80 style microprocessor the simplest test program is a BLANK EPROM If used properly this program will find any shorted address lines any shorted or open data...

Page 21: ...he Z80 writes out the address 0039 on the stack Note that this takes two write cycles Each time the Z80 writes this out the stack address changes so the address lines will count through all address Th...

Page 22: ...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 2m...

Page 23: ...leads set to 12 0V Charger voltage Positive battery lead 8 6V To check out the charger circuit install cells Positive battery lead 5 4V to 8 6V depending on batteries state of charge On Off switch Pre...

Page 24: ...se U13 pin 14 full scale input About 30 milliseconds width pulse Lamp Press the lamp key All eight lamps light up Keys For each key observe about five volts on the indicated pin Press the key and see...

Page 25: ...st 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 tur...

Page 26: ...test Master 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 f...

Page 27: ...esistor in series with the Excitation lead is for temperature compensation It is a balco resistor that change resistance with temperature to maintain a constant signal voltage These resistors are spec...

Page 28: ...ding 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 b...

Page 29: ...fy 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 s...

Page 30: ...workstation The main printed circuit board is subject to damage by electrostatic discharge Disassembly 1 Remove all 10 bezel screws 2 Detach keyboard assembly unplug keyboard connector and set aside 3...

Page 31: ...static controlled workstation The main printed circuit board is subject to damage by electrostatic discharge Disassembly 1 Remove all 10 bezel screws 2 Detach keyboard assembly and set aside Do not un...

Page 32: ...endix A for details 27 Replace insulator on back of summing board 28 Return summing board in housing 29 Place circuit board into housing Be careful not to pinch the wires between the battery tube and...

Page 33: ...ccessible 6 Turn scale ON 7 Wait for scale to warm up 8 Zero the scale 9 Apply 5000 lb load to load cell 1 and record weight 10 Record displayed weight 11 Apply a 5000 lb load to front load cell using...

Page 34: ...e 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...

Page 35: ...and materials In addition the usual workbench and good lighting the following list of tools and materials would be necessary to set up a complete PT 300 service station Twenty thousand pound calibrati...

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 124 174...

Page 37: ...t Transmit Data format M Kg Format A_O_ XXXXXXX _Lb CR LF 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...

Page 38: ...18 1 01uF Ceramic Disc 50v Radial Leads C2 C14 C15 C21 C22 C23 C2 4 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 19 0 1uF Polypropylene 100v Axial Leads C10 C11 C8 3 0 1uF Ceramic Disc 25v Radial L...

Page 39: ...R4 1 5M ohm w 5 R33 1 1N914 D2 D3 D18 D19 4 1N4001 D1 D5 D17 3 1N5711 D8 1 1N5240 D4 1 1N5233B D6 D7 2 LM340LA 5 Q3 1 2N2222 Q2 Q4 Q5 Q7 Q9 5 2N4402 Q6 Q8 Q10 3 4N35 U15 U16 2 74HC08 U14 1 74HC14 U3 1...

Page 40: ...RD PARTS LIST PT300 Summing Board Rev 1 Reference Quantity 14pin Dual Row 90 Header 3M 2414 5222TG JP1 1 10K ohm Trim Pot R1 R2 R3 R4 4 47M ohm w 1 R6 1 15M ohm w 5 R8 1 22M ohm w 5 R7 1 500 ohm pot R...

Page 41: ...te operating point The Deadload or Tare must be set with no weight on the scale This is not a regular maintenance item it should only need to be adjusted when changing a circuit board or load cell Ple...

Page 42: ...will either increase or decrease depending on the signal coming from the load cells 3 If the raw counts are lower than 1500 or go down as weight is applied it means that the negative signal is too hi...

Page 43: ...s series 274 301 330 365 392 If you need less span run out of travel going counter clockwise select the next higher resistor in the series These resistors must be 1 tolerance parts With the revision B...

Page 44: ...ober 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 Ca...

Page 45: ...PT300 Service Manual Rev B October 2000 44 Appendix B Schematics...

Page 46: ...PT300 Service Manual Rev B October 2000 45...

Page 47: ...PT300 Service Manual Rev B October 2000 46...

Page 48: ...PT300 Service Manual Rev B October 2000 47 Totalizing cable...

Page 49: ...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: ...PT300 Service Manual Rev B October 2000 50 Internal Cable Assembly...

Page 52: ...PT300 Service Manual Rev B October 2000 51 Parts...

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