Troubleshooting And Repair Of The 6V2100 Multitach{0781} Caterpillar

Troubleshooting And Repair Of The 6V2100 Multitach{0781}

Usage:

General Information

NOTE: Use the parts layout, schematic diagram, block diagram and parts list on pages 24, 25, 27 and 28 respectively for reference throughout this instruction.

The 6V2100 Multitach contains a microcomputer that calculates R/MIN (revolutions per minute) from the input signals and indicates the R/MIN calculation on an LCD (liquid crystal display). The multitach receives input signals through either the PHOTO IN or MAG IN connectors. All signals entering the multitach go through protection circuitry and are conditioned for compatability with other multitach circuits.

The MAG/PHOTO SELECT circuitry allows only one of the conditioned signals to be amplified and applied to the microcomputer. Either the MAG or the PHOTO input can be selected for amplification and input to the microcomputer by pressing either the MAG or PH touch switch on the front panel of the instrument. Either the MAG light or the PHOTO light will be on to indicate which signal is being sent to the microcomputer. If no signal is being sent to the microcomputer, the no input signal detection circuitry will turn on the NO INPUT SIGNAL light.

The microcomputer has been programmed to calculate and display the R/MIN reading. A 3.58 MHz crystal provides the time base for the R/MIN calculation. The microcomputer requires information on the number of pulses it will receive for each revoluttion of the rotating part (P/REV) before the R/MIN calculations can be made. The P/REV information is supplied to the microcomputer by pressing the proper touch switches on the front panel. The microcomputer will send the proper code to the display drivers so the calculated R/MIN can be observed on the display.

The display drivers drive the LCD by converting the microcomputer output code into an oscillating code that will turn on the correct segments of the LCD. The LCD requires an alternating voltage for its operation. The 150 Hz back plane oscillator/driver circuitry provides this alternating voltage to the display. The 5 Volt power supply circuitry uses a switching power supply to convert an 11 - 40 VDC input to a 5 Volt @ 300 mA supply for the multitach circuitry.

Circuit Descriptions

(A) Signal Input And Conditioning

The multitach receives signals from a signal generating device through connectors J1 and J2 [labeled PHOTO IN and MAG IN on the connector panel]. The multitach receives signals from the 6V3136 Photo Pickup through connector J1. Power is applied to the photo pickup lamp across pins 5 and 3. The voltage drop across R2 reduces the voltage applied to the lamp from approximately 5 Volts to approximately 2 Volts. Multitach circuit ground is provided to the photo pickup shield on pin 1. An application of 5 Volts is given to the photo transistor collector on pin 4. The generated signal, the output of the photo transistor, is received by the multitach through connector J1 on pin 2.

The signal from the photo pickup must be conditioned for compatability with the rest of the multitach circuitry. The signal from the photo pickup is a sinusoidal waveform with approximately 3 VDC offset. The 3 VDC offset is eliminated by blocking capacitor C1. Resistors R1, R4 and R6 serve as suppression circuitry. Diodes D6 and D7 "clip" the signal, eliminating any signal voltages less than -0.7 Volts and greater than +0.7 Volts respectively. Resistor R12 limits the current through IC7A.

Connector J2 receives signals from signal generating devices such as the 5P7360 Tachometer Generator or a magnetic pickup. The signal from one of these signal generating devices can be of several forms; the main requirement being that its amplitude must be between 0.1 Volt and 100 Volts.

NOTE: Signals over approximately 30 Volts peak [less than 30 Volts if multitach does not have change "A" described on page 23] may cause interference between the PH and MAG inputs.

The LO input of the generating device is tied to the multitach circuit ground. The signal is received from the signal generating device on the HI (center connection) of J2. Devices connected to J2 do not require power from the multitach. The current provided by the device connected to J2 is limited by resistors R3 and R5. Voltage spike protection is provided by capacitor C5. Diodes D8 and D9 "clip" the signal, eliminating any signal voltages less than -0.7 Volts and greater than +0.7 Volts respectively. Resistor R13 and capacitor C11 filter the conditioned mag signal. Diode D11 eliminates voltage less than -0.7 Volts.

(B) Amplifier And Switch

The microcomputer can count only one of the conditioned signals at a time. The amplifier and switch circuitry provides a means by which only the signal selected by the mag/photo select circuitry will pass through an amplifier to the microcomputer.

The mag and photo signal amplifiers are made up of comparators IC7B and IC7A respectively, and their associated components. Both comparators are set up so the result of a voltage less than .06V on the selected amplifier input will be +5V on the amplifier output, and the result of a voltage greater than .06V on the selected amplifier input will be zero (0) Volts on the amplifier output. The comparators in IC7 have open collector outputs. Their outputs will be low (ground) when the plus (+) input is less than the minus (-) input, and will be floating when the plus (+) input is greater than the minus (-) input. However, R14 serves as a pull-up so the voltage at the output of the signal amplifiers will be +5V when both comparator outputs are floating.

A voltage divider made up of R11, R16 and R15 divides 5V down to .06V which is applied to the plus (+) input of comparators IC7A and IC7B. The signal amplifiers thus provide zero (0) Volts to the microcomputer when the voltage of the selected amplifier input is greater than .06V, and provide 5V to the microcomputer when the selected amplifier input is less than .06V. Diode D10 provides hysteresis to the comparators by changing the reference voltage on pins 5 and 7 to .03V whenever the outputs of IC7A and IC7B go to zero (0) volts. Noise suppression is provided by C21.

The switch circuitry grounds the signal not selected, removing that signal from the rest of the multitach circuitry. The signal selected is not grounded and is amplified. The switch for the mag signal is Q3. When the photo signal is selected, Q3 is turned on by the mag/photo select circuitry, and the mag signal is pulled to ground. The switch for the photo signal is IC7D. When the mag signal is selected, the mag/photo select circuitry will cause the output of IC7D to be low, pulling the photo signal to ground.

(C) Mag/Photo Select Circuitry

Signal selection is accomplished by pressing either the MAG or PH touch switch on the front panel of the instrument. The touch switch activates a flip-flop arrangement that controls the MAG and PHOTO lights, and the switch section of the amplifier switch circuitry.

The flip-flop arrangement consists of Q1, Q4, Q20, Q21 and R22. When the PH touch switch is pressed, the base of Q1 is pulled to ground by the touch switch and Q1 is turned off. When Q1 is turned off, its collector is pulled up to approximately 2V by R21. When the collector of Q1 is at 2V, Q4 is turned on through one of the resistors in R22 so its collector is pulled to ground. With Q4's collector at ground and Q1's collector at 2V, the plus (+) input of IC7D is greater than the minus (-) input; this results in a floating output that does not interfere with the conditioned photo signal. Q3 is turned on through one of the resistors in resistor network R22 [located between pins 9 and 10] to prevent mag signal from being sent to the microcomputer. When collector of Q1 is at 2V, photo light D4 is turned on to indicate photo signal is being sent to the microcomputer. If PH switch is pressed again, there will be no change.

When the MAG touch switch is pressed, the base of Q4 is pulled to ground by the touch switch and Q4 is turned off. When Q4 is turned off, its collector is pulled up to approximately 2V by R20. When the collector of Q4 is at 2V, Q1 is turned on through one of the resistors in R22 so its collector is pulled to ground. With Q1's collector at ground, Q3 is turned off so it does not interfere with the mag signal. When Q4's collector is at 2V and Q1's collector is at ground, the plus (+) input of IC7D is less than the minus (-) input. This results in an IC7D output of zero (0) Volts that grounds the photo signal, preventing it from being sent to the microcomputer. When Q4's collector is at 2V, the MAG light D3 is turned on to indicate that the mag signal is being sent to the microcomputer. If the MAG touch switch is pressed again, there will be no change.

(D) No Input Signal Circuitry

The no input signal circuitry turns on the NO INPUT light when no signal is being sent to the micro computer. The output of the signal amplifiers will be approximately a steady 5V when no signal is present, and the amplifier output will be alternating between zero (0) Volts and 5V when a signal is present. R18 and C12 make up an RC network that averages the amplified signal voltage. When this averaged voltage is greater than approximately 3V [when no signal is being sent to the microcomputer], Q2 is turned on; turning on the NO INPUT light. R19 reduces the 5V supplied on Q2's emitter to approximately 2V to operate the LED. When the averaged voltage is less than approximately 3V [when no signal is being sent to the microcomputer], Q2 is turned off and the NO INPUT light is also turned off. D12 eliminates any averaged voltage less than -0.7V.

(E) Microcomputer Inputs

Microcomputer IC6 is a device that has been programmed during manufacture. Although it does contain a program, the IC6 still requires other inputs before it can perform the program properly. The microcomputer must start at the beginning of the program every time the multitach is turned on. The microcomputer reset [pin 39] will start the program at the beginning every time its applied voltage is approximately zero (0) Volts and the microcomputer already has power applied to it. During power-up when voltage is first applied to connector J3, pin 39 must stay below 0.8V until the voltage applied to pin 40 [microcomputer power] is greater than 4.5V. The internal circuitry of IC6's reset function has a 5V pullup so after power-up, pin 39 will go high allowing the program to start. C6 slows the rise time of the voltage from the pullup so the voltage on pin 39 will not exceed 0.8V before pin 40 exceeds 4.5V. D5 serves as a quick discharge, quickly draining the voltage on C6 after turn-off so C6 will be able to hold reset below 0.8V if the power is immediately turned back on. C7 prevents rapid flucuations on pin 40.

IC6 requires an oscillating input to provide a clock signal. Y1 provides a 3.58 MHz clock signal to pin 1 of IC6. IC6 pin 2 supplies Y1 with approximately 1.5VDC. C19 is used to adjust the frequency of the clock signal slightly for greater accuracy.

In order to calculate R/MIN, the microcomputer must know how many pulses it will receive on its signal input for every revolution of the engine's crankshaft. When the P/REV touch switch is pressed on the front of the instrument, pin 38 [IC6's external interrupt] is pulled low. When pin 38 is pulled low, the microcomputer will stop the program it is running, and go to the section of the program that will accept input. After the P/REV touch switch has been pressed, IC6 will accept instructions from the touch switch on pins 22, 23, 24 and 27 through 37. Pressing the CLR switch will cancel the number of pulses per revolution that IC6 is using. Pressing the number switches will enter the new P/REV number into the microcomputer. Pressing the R/MIN switch will start the revolutions per minute calculation section of the program. Microcomputer IC6 receives the conditioned and amplified speed input signal on pin 25.

(F) Microcomputer Program

The microcomputer program has two major sections, P/REV input and R/MIN calculation. The microcomputer IC6 will operate in the P/REV input section of its program when voltage is first applied to connector J3, or when the P/REV touch switch is pressed. When the multitach is turned on, this section of the program will send the proper code to the display drivers so a flashing zero (0) appears on the LCD (liquid crystal display).

When the P/REV touch switch is pressed, the P/REV number will flash on the LCD. If a P/REV number has not been entered since turn on, the P/REV number will be either 10 or the number selected by the auto-programmer [if one is installed]. A new P/REV number can be entered any time the LCD is flashing, either when the multitach is turned on or after the P/REV switch is pressed. As the P/REV number is entered on the touch switch, IC6 will send the proper code to the display drivers so each digit is displayed on the LCD as it is entered. IC6 will remain in the P/REV section of the program until the R/MIN key is pressed or until the multitach is turned off.

The R/MIN section of the microcomputer program calculates the R/MIN from signal inputs and from the P/REV number. This section then sends the proper code to the display drivers so the calculated R/MIN appears on the LCD. IC6 will begin calculating R/MIN after the P/REV number has been entered and the R/MIN touch switch on the front panel has been pressed.

IC6 calculates R/MIN from the amount of time it takes to receive the number of signal pulses for either 4 or 14 revolutions of the rotating part. When the R/MIN switch is pressed, IC6 calculates how many pulses it will receive for 4 revolutions of the rotating part from the P/REV. IC6 will then count that number of pulses and check the elapsed time [the crystal Y1 provides a 3.58 MHz clock signal for measuring elapsed time]. The information on the time it took for 4 revolutions is then used to calculate R/MIN. If the calculated R/MIN is less than 400, IC6 will send the proper code to the display drivers so the calculated R/MIN will appear on the LCD. If the calculated R/MIN is equal to or greater than 400, IC6 will continue to calculate the number of pulses it will receive for 10 more revolutions; remember that number of pulses; check the elapsed time, and recalculate R/MIN using the new information. If the recalculated R/MIN is equal to or greater than 400, IC6 will send the proper code to the display drivers so the recalculated R/MIN will appear on the LCD.

Every time an R/MIN reading has been displayed, the microcomputer will repeat the pulse counting sequence for a new R/MIN calculation that will update the old. R/MIN will be recalculated approximately every second when R/MIN is greater than 400, and a maximum of six seconds when the R/MIN is less than 400. IC6 will remain in the R/MIN calculation section of the program until the P/REV touch switch is pressed, or until the multitach is turned off.

(G) Display Driver Inputs

Each of the display drivers [IC1 through IC5] controls a character location, either a digit or the decimal points, of LCD1 by turning on the different segments of each digit or decimal point so the characters called for by IC6 are displayed.

The following table lists the character location that each driver controls.

The character that each driver will display is determined by the voltage code each driver receives from IC6 whenever IC6 updates the display. This voltage code consists of zero (0) Vdc (nominal) and 5 Vdc (4 Vdc to 5 Vdc) voltages applied to driver input pins 2 through 5 by IC6. After receiving the voltage code, the drivers will turn on, and keep the proper display segments on, until a new code is received from IC6.

The voltage code for a single character appears on all driver code inputs simultaneously, therefore, IC6 must tell each driver when to latch [sample and hold] a voltage code so each driver sees only its code, and not a code intended for another driver. IC6 controls the latching of the code with IC6 pins 8 through 12, one of which is tied to pin 1, the latch, of each of the drivers. A display driver will latch the code from IC6 whenever the voltage on its pin 1 is approximately 5V.

The following table shows the IC6 pin that controls the latching of each individual driver.

After the microcomputer [IC6] determines the characters that are to appear on the display, it sends out the voltage code for a blank display and has all of the drivers latch this code at the same time. The voltage codes for the characters that are to appear on LCD1 follow immediately after this blank code. The time between the blank code and the character codes is so short that the display will not actually become blank. The character voltage codes that follow the blank code appear on the driver code inputs in the following order.

If a display driver controls a character location that is to remain blank, it will not latch another voltage code after latching the blank code. The following table shows the characters that can be displayed, and the voltage code that would be latched by the display drivers on the display driver pins [pins 2 through 5] in each case.

The relationship between the voltage codes and the latch signals can be observed on an oscilloscope, and by looking at the timing diagram on the next page of the example shown below. See USE OF OSCILLOSCOPE FOR CIRCUIT OPERATION CHECKS for more information on oscilloscope traces.

EXAMPLE: If the number 857 appears on LCD1, the display drivers must latch the following codes.

The following are timing diagrams of IC1 - IC5 inputs when 857 is appearing on LCD1.

Since the decimal points and the 1000's digit are blank, IC5 and IC4 do not latch a code after latching the blank code. IC1, IC2 and IC3, which are to display the numbers 7, 5 and 8 respectively, latch the proper voltage codes immediately after latching the blank code.

(H) Display Driver Outputs

The display drivers, IC1 through IC5, turn on appropriate LCD segments so the number called for by the microcomputer is displayed. Each display segment is controlled by one driver pin. The following shows each display segment and its corresponding driver pin.

The display drivers control the display segments with an oscillating voltage that has the same frequency (approximately 150 Hz) as the voltage applied to the back plane of the LCD. When the output of a driver pin is exactly the same as the back plane voltage, the segment that the pin controls is off. When the output of a driver pin is the inverse (180 degrees out of phase) of the back plane voltage, the segment that the pin controls is on. The difference between a signal sent to a segment that is to be turned on, and a signal sent to a segment that is not to be turned on, can be observed in the timing diagram of the following example or on an oscilloscope. Refer to USE OF AN OSCILLOSCOPE FOR CIRCUIT OPERATION CHECKS for more information on oscilloscope traces.

EXAMPLE: The character 7 appears as the 1's digit character on LCD1. To display the number 7, segments a, b and c of the 1's digit must be turned on by IC1 pins 9, 10 and 11 respectively; while segments d, e, f and g, that are controlled by IC1 pins 12, 13, 15 and 14 respectively, remain off. The timing diagrams of IC1's outputs are as follows.

(1) 150 Hz Back Plane Oscillator/Driver Circuitry

Liquid crystal displays (LCD's) require an oscillating voltage as a power source. This voltage is applied to the LCD back plane, and is supplied by the 150 Hz back plane oscillator/driver circuitry. The multitach back plane driver consists of IC7C, C8, R17, R8, R7, R9 and R10. These components form an oscillator with an output of approximately 5V in amplitude and 150 Hz in frequency.

(J) 5V Power Supply Circuitry

The power supply circuitry of the multitach converts the 11 to 40 Vdc input to a 5 Vdc @ .3A supply for the rest of the multitach circuitry. Steady state regulators cannot dissipate the power released in this conversion, so a switching regulator is used to provide the 5 Vdc supply.

(K) Application Of Power To The Multitach

Power from an 11 to 40 Vdc source is applied to input connector J3 of the multitach. Fuses F1 and F2 are fast blow, 1 amp fuses that protect the multitach by "blowing" when the voltage applied to J3 produces a current in the multitach that exceeds a safe level. Diode bridge D1 allows the power applied to connector J3 to be non-polarized; either positive or negative supply terminal can be connected to either pin of J3. Filter capacitor C13 helps reduce voltage fluctuations, and removes electrical noise.

(L) 36V Preregulator

A preregulator, consisting of D13, Q5, R23 and C14, limits the voltage applied to the rest of the power supply circuitry to under approximately 36V. When the voltage applied across zener diode D13 reaches 36V, the voltage is "clamped"; therefore, if the voltage across the (+) and (-) terminals of the diode bridge exceeds 36V, the voltage at base of Q5 will remain at 36V. The voltage at Q5's emitter must be less than that of the base when Q5 is on [voltage supplied at Q5's emitter must be less than approximately 36V]. Since Q5 limits voltage to 36V, any voltage above this will be given off as heat by Q5. This causes Q5 to become hot. Prolonged operation above 40V, or a power source with noise transients above 150V can damage Q5. Preregulator Q5 is designed to operate continuously on input voltages up to 40V with 150V noise transients, 1 millisecond in duration and not more than one every 5 seconds.

(M) Switching Power Supply

The switching power supply integrated circuit IC8, along with switching transistor Q6 and other components, converts the filtered dc output voltage from the 36V preregulator to a regulated number of voltage pulses that are filtered by additional components to provide a 5Vdc output. IC8 regulates the voltage pulses by monitoring the 5Vdc output and allowing pulses to be produced only when it falls below 5Vdc. The functions contained in IC8 that are used in this application are a 1.25V reference voltage, a voltage comparator, an oscillator, an AND gate, a flip-flop, and two transistors. The 36V preregulator supplies power to IC8 pin 13.

The switching regulator IC8 monitors the 5Vdc output with its comparator. The 1.25V voltage reference on pin 8 is compared to a voltage equal to 1/4 that of the 5Vdc output. The 5V output voltage is divided across R28 and R24 so when the output is exactly 5V, the voltage between R28 and R24 is a nominal 1.25V. The divided voltage is applied to pin 10, the (-) input of the comparator; and the 1.25V reference is applied to pin 9, the (+) input of the comparator. When the 5Vdc output is greater than or equal to 5V, the divided voltage will be greater than or equal to the reference, and the comparator output will be low. When the 5Vdc output is less than 5V, the divided voltage will be less than the 1.25V reference, and the comparator output will be high.

The output of the internal AND gate will determine whether voltage is to be provided to the filter circuitry. One input to the AND gate is the output of the comparator. The other input is the output of IC8's oscillator; the frequency of which is determined by the value of the timing capacitor C15, which is tied to pin 12. The output of the AND gate will be low, and voltage will not be applied to the filter circuitry when the comparator output is low [when 5Vdc output is greater than or equal to 5V]. The output of the AND gate will be high, and voltage will be applied to the filter circuitry when both the comparator output and the oscillator output are high; this happens only when the 5Vdc output is less than 5V. The oscillator input causes the output of the AND gate to oscillate when the voltage of the 5Vdc output is less than 5V. The voltage applied to the filtering circuitry is controlled by the output of the AND gate; therefore, the voltage applied to the filter circuitry is in the form of voltage pulses.

The output of the AND gate drives a flip-flop which is reset by the oscillator. The flip-flop drives IC8's two transistors, Q7 and Q8, which drive the external switching transistor Q6. The flip-flop turns on Q7 when the AND gate output is high. When Q7 is on, there is a voltage drop across the internal resistor that turns on Q8. The collectors of Q7 and Q8, pins 15 and 16, drive Q6.

The voltage from the 36V preregulator is provided through R26 to the emitter of the external switching transistor Q6. When Q6 is turned on, the voltage from the preregulator is applied to the filter circuitry; Q7 and Q8 turn on Q6 by pulling its base low when the output of the AND gate is high. The base of Q6 and collectors Q7 and Q8 are pulled high by R25 when the transistors are not on. Electrical noise across R25 is suppressed by C18. R27 limits the base current of Q6.

IC8 provides overcurrent protection to the switching power supply by turning off Q6 when the current flowing through it exceeds a safe level. The voltage drop across R26 is directly proportional to the current flowing through Q6. IC8 monitors the drop across R26 on pins 13 and 14, and will shut off the oscillator [thereby turning off Q6] when the current/voltage exceeds a safe level. R26's resistance is of such a low value, it will have little effect on the voltage and current supplied to Q6.

The filter circuitry converts the voltage pulses from Q6 into a dc voltage. Negative voltage components are eliminated from the pulses by D14. The major part of the filtering is done by L1 and C17 which convert the positive voltage pulses into a dc voltage. Noise suppression is provided by C20. An RC network consisting of R29 and C16 smooths the 5Vdc output an additional amount.

Troubleshooting

The following lists and procedures provide information for updating the multitach, and for locating defects in the multitach circuits. The section MULTITACH CHANGES may be used to ensure that your multitach is fully updated; make these changes only if required under comments. The section PROBLEMS AND CAUSES should be used as a guide for determining the area of the circuitry that is defective. The sections USE OF THE 6V3030 DIGITAL MULTIMETER FOR CIRCUIT VOLTAGE CHECKS and USE OF THE OSCILLOSCOPE FOR CIRCUIT CHECKS show methods for determining which component(s) within a circuit are defective.

(A) Multitach Changes

(B) Problems And Causes

(C) Use Of The 6V3030 Digital Multimeter For Circuit Voltage Checks

The following procedures show how to use the 6V3030 Digital Multimeter (or equivalent) for locating defects in the power supply, mag/photo select, and the no input circuits. In addition to the digital multimeter, the following equipment is also needed: a) a 24-40Vdc power supply capable of a 300mA output; b) a 5P7366 Power Cable; and c) a 5P9698 Calibrator.

Connection Of Test Equipment To The Multitach

Remove six screws (1) from rear cover (2) of the multitach. Pull straight out to remove the rear cover. If the multitach has an auto programmer (3) in place of the rear cover, fold out the outo programmer and disconnect connector (4) from connector (5).

Connect the 5P7366 Power Cable to connector J3 (labeled 11-40Vdc). Connect the two clips of the power cable to the two terminals of the power source. Since the multitach power input is non-polarized, either positive or negative supply terminal can be connected to either clip of the power cable.

Test Conditions

The following conditions are assumed to exist during all tests unless stated otherwise:

1. All voltage measurements are approximate unless accuracy is specified.

2. All tests are conducted with 24 Vdc applied to J3, except for that part of the power supply test that requires 40 Vdc to be applied to J3.

3. All voltage measurements were taken with respect to multitach circuit ground found on the low input of J2.

4. The voltmeter must have a minimum input impedance of 22 M Ohms.

5. All voltages measured are direct current (dc).

6. No pickups are installed on the connector panel unless specified.

7. The additional conditions for each test are met.

NOTE: The printed circuit board has a clear protective coating. Use the sharp pointed probes from the 6V3032 Deluxe Lead Kit to penetrate the coating to make contact.

Power Supply Circuit - Voltage Test Points And Nominal Voltages

NOTE: This test is first performed with 24Vdc at J3, then 40Vdc at J3.

Mag/Photo Select Circuit - Voltage Test Points And Nominal Voltages

NOTE: This test checks the circuit that controls the MAG and PHOTO lights, and selects the signal desired for R/MIN calculations. For the section of the test that requires MAG light on, press MAG on the front panel. For the section that requires PHOTO light on, press PH on front panel.

No Input Circuit - Voltage Test Points And Nominal Voltages

NOTE: This test checks the circuit that senses whether a signal is being sent to the microcomputer, and turns on the NO INPUT light. To test this function, the voltages must be tested with and without a signal being sent to the microcomputer. Connect 5P9698 Calibrator to connector J2 (labeled MAG IN). Press MAG switch on front panel; the MAG light should come on. Turn off calibrator for the NO INPUT section of the test. Turn calibrator on to 100Hz for WITH INPUT section of the test.

(D) Use Of The Oscilloscope For Circuit Operation Checks

The following procedures show how to locate defects in the multitach circuitry that cannot be detected with a digital multimeter. In addition to an oscilloscope, the following equipment is needed: a) a 24Vdc power supply capable of a 300mA output; b) a 5P7366 Power Cable; c) a 5P9698 Calibrator; d) a 6V3136 Photo Pickup; and e) a fluorescent light.

Connection Of Test Equipment To The Multitach

Remove six screws (1) from rear cover (2) of the multitach. Pull straight out to remove the rear cover. If the multitach has an auto programmer (3) in place of a rear cover, fold out the auto programmer and disconnect connector (4) from connector (5).

Connect the 5P7366 Power Cable to connector J3 (labeled 11 to 40Vdc). Connect the two clips of the power cable to the two terminals of the 24V power supply. Since the multitach power input is non-polarized, either positive or negative supply terminal can be connected to either clip of power cable.

Test Conditions

The following conditions are assumed to exist during all tests unless stated otherwise;

1. All traces are approximate unless accuracy is specified.

2. All traces are conducted with 24Vdc applied to J3.

3. All traces are taken with respect to multitach circuit ground found on the low input of J2. Connect the oscilloscope ground lead to this point.

4. All voltages measured are direct current (dc).

5. No pickups are installed on the connector panel unless specified.

6. The additional conditions for each test are met. If the additional conditions cannot be met due to a problem in the multitach [for example, the MAG or PHOTO lights will not come on], the problem should be corrected first, if possible.

NOTE: The printed circuit board has a clear protective coating. Use a sharp, pointed oscilloscope probe, or carefully scrape away the coating from the area to be checked in order to make contact.

Photo Input - Oscilloscope Test Points And Nominal Traces

NOTE: This section of the test procedure tests most of the components that affect the signal that is input through J1 (labeled PHOTO IN) by following the signal from the connector, through conditioning, selection and amplification, to its application to the microcomputer.

Test Conditions

1. PHOTO light on.

2. The 6V3136 Photo Pickup connected to J1 (labeled PHOTO IN).

3. The photo pickup is held directly toward and approximately 8 inches from the fluorescent light operating on 50 or 60 Hz ac voltage so the NO INPUT light goes off. NOTE: Frequency of waveforms for 50Hz fluorescent light will be different from 60Hz fluorescent light.

4. The oscilloscope horizontal sweep is set at 10 ms/DIV.

5. The oscilloscope vertical attenuation and probe placement are as specified for each trace.

6. The solid line is 0 Volts.

Photo Input Signal

Vertical attenuation at 2 V/DIV.

Probe at junction of R1 and C1.

"Clipped" Photo Signal

Vertical attenuation at 0.5 V/DIV.

Probe at junction of D7 and R12.

Photo Input To Amplifier

Vertical attenuation at 0.5 V/DIV.

Probe at IC7 pin 4.

Photo Input To Microcomputer

Vertical attenuation at 2 V/DIV.

Probe at IC6 pin 25.

Mag Input - Oscilloscope Test Points And Nominal Traces

NOTE: This section of the test procedure checks most of the components that affect the signal that is input through J2 (labeled MAG IN) by following the signal from the connector, through conditioning, selection and amplification, to its application to the microcomputer.

Test Conditions

1. MAG light on.

2. The 5P9698 Calibrator is connected to J2 (labeled MAG IN).

3. Set the 5P9698 Calibrator to 100Hz.

4. Set oscilloscope horizontal sweep at 10 ms/DIV.

5. The oscilloscope vertical attenuation and probe placement are as specified for each trace.

6. The solid line is 0 Volts.

Mag Input Signal

Vertical attenuation at 1 V/DIV.

Probe at junction of R3 and R5.

"Clipped" Mag Signal

Vertical attenuation at 1 V/DIV.

Probe at junction of D9 and R13.

Mag Input To Amplifier

Vertical attenuation at 1 V/DIV.

Probe at IC7 pin 6.

Mag Input To Microcomputer

Vertical attenuation at 2 V/DIV.

Probe at IC6 pin 25.

Clock - Oscilloscope Test Points And Nominal Trace

NOTE: This section verifies the microcomputer time base by checking the clock signal entering IC6.

Oscilloscope horizontal sweep at 1 microsecond/DIV.

Oscilloscope vertical attenuation at 1 V/DIV.

Probe at IC6 pin 1.

Display Driver Inputs - Oscilloscope Test Points And Nominal Traces

NOTE: This section checks the inputs to the display drivers, and the latch and code ouputs from IC6.

Test Conditions

1. The traces are dual traces. The top waveform is one of the code inputs (driver pins 2-5), and the bottom waveform is one of the latches (driver pin 1).

2. The most negative point on each waveform is 0 Volts.

3. Oscilloscope is in chopped mode.

4. Set oscilloscope horizontal sweep at .2 ms/DIV.

5. Oscilloscope vertical attenuation is set at 5 V/DIV.

6. The following traces are only examples of what can be observed. The code waveform will differ depending upon the characters to be displayed on LCD1. The number of latch pulses observed for each code sequence depends on what the driver is to display, one pulse for a blank, or two pulses for a character.

7. Both waveforms of the dual trace are triggered from the same source.

Character to be displayed is a blank (only one latch)

Character to be displayed is not a blank (two latches, one for the blank and the other for the code of the character to be displayed.)

Display Driver Outputs - Oscilloscope Test Points And Nominal Traces

NOTE: This section checks the outputs of the display drivers and LCD1.

Test Conditions

1. The traces are dual traces. The top waveform is the driver output, and the bottom waveform is the 150Hz oscillator found on pin 6 on all of the drivers.

2. The most negative point on each waveform is 0 Volts.

3. Oscilloscope is in the chopped mode.

4. The oscilloscope horizontal sweep is set at 2 ms/DIV.

5. Oscilloscope vertical attenuation for both waveforms is 5 V/DIV.

6. The probe location for the top waveform is on one of the driver output pins 9-15.

7. The probe location for the bottom waveform is on driver pin 6.

8. Both waveforms of the dual trace are triggered from same source.

Driver Output For Turned On LCD1 Segment

Driver Output For Turned Off LCD1 Segment

Repair Of The 6V2100 Multitach

(A) Removal Of The Rear Cover

Remove six screws (1) from rear cover (2) of the multitach. Pull straight out to remove the rear cover. If the multitach has an auto programmer (3) instead of a rear cover, fold out the auto programmer and disconnect connector (4) from connector (5).

(B) Removal Of Circuit Board

1. Put the multitach face down on a soft surface to prevent damage to the face. Use a screwdriver to remove six screws (1) from outer edge of printed circuit board. Do not remove two screws (2).

2. Hold connector panel (3) with one hand, and upright capacitor (4) with the other hand. Carefully lift printed circuit board (5) out of plastic cover. Do not put excessive strain on ribbon cable (6).

3. Use two small screwdrivers and your thumbs as shown to disconnect touch switch connector (7) by gently pulling it toward the end of the circuit board and off the pins.

(C) Replacement Of Integrated Circuits

1. Remove the rear cover from the multitach as shown on page 19.

2. To remove IC6, IC7 and IC8, use the hook end of 5P1720 Seal Pick (1) to carefully remove the integrated circuit as shown.

NOTE: A clear protective coating was used on earlier multitachs to cover the IC sockets. If the multitach has this coating, removal of the IC's can be made easier by heating the printed circuit board to approximately 60°C (140°F). Usually the socket will also need replacement, as well as the integrated circuits, since the coating can interfere with socket connections.

3. To remove IC1, IC2, IC3, IC4 and IC5, remove the circuit board from the front cover as shown on page 19. Use a soldering iron to heat the solder; remove the integrated circuit.

IMPORTANT: When installing an integrated circuit, always make sure that pin 1 on the IC is mated with socket 1 on the printed circuit board. Pin 1 on the IC is located at the notched end (or the end with a dot) of the IC. Socket 1 is marked on the printed circuit board.

(D) Replacement Of Front Panel Touch Switch

1. Remove the rear cover and circuit board as shown on page 19.

2. Use a small screwdriver to lift up on one corner of panel (1). Peel off the touch switch panel.

3. Clean front cover (2) with a mild detergent and water to remove the dirt and oil film. Make sure the front cover is completely dry before installing the new touch switch panel.

Show/hide table

NOTICE

Do not use aromatic hydrocarbons or chlorinated solvents for cleaning the multitach case. These chemicals will cause damage to the case.

4. Peel off the middle section of the paper that protects the touch panel adhesive. Insert the touch panel connector through slot (A) on the front cover. Put the windows of the touch panel in alignment with holes (B) on the front cover; press the center section of the touch panel to the front cover. Remove the remainder of the protective paper, and press the panel to the front cover.

NOTE: It may be necessary to cut a small section from the bottom of the touch panel in order to align the windows in the touch panel with the holes in the front cover.

(E) Removal Of Display Assembly

1. Remove the rear cover and circuit board as shown on page 19.

2. While holding display assembly (1) around the edges, use a small screwdriver to remove two screws (2). Remove the display assembly from the printed circuit board. Be careful not to touch the display except at the edges.

3. If flexible conductors [zebra strips] (3) are to be removed, use tweezers to carefully remove them from the slots in the display bracket. Do not touch the flexible conductors; skin contact can leave oil on the conductors.

(F) Cleaning The Display Assembly

1. The LCD's can be cleaned by gently wiping them with a soft c cloth. IMPORTANT: Rubbing the LCD too hard can remove the contacts deposited in the glass.

2. The flexible conductors (zebra strips) can be cleaned by dusting them with a camel's hair brush. If grease or fingerprints are on the conductors, the conductors may be washed with clean alcohol, and then air dried. Do not wipe the flexible conductors with any material that could leave lint or other deposits on the flexible conductors.

3. Contacts (1) on the circuit board can be cleaned with a pencil eraser.

(G) Installation Of Display Assembly

1. Put display bracket (1) in position on the printed circuit board. Use tweezers to carefully position flexible conductors (2) in slots (A) of bracket (1).

2. Being careful to touch display (3) at the edges only, hold the display to the light and observe the numbers and decimals "8.8.8.8". Put display (3) in position on bracket (1) so the decimals are at locations (B).

3. Install display cover (4) and two screws (5). Make sure the screws are tightened evenly so the display and flexible conductors make good contact. Install the printed circuit board and rear cover.

NOTE: If the display does not operate correctly after assembly of the multitach, press the display cover while the multitach is on. If this corrects the problem, either cover (4) is not fastened securely or the terminals are oxidized. If the correct digits do not appear, make sure that the display has not been installed upside down.

Update Modifications

Multitachs built before July 1, 1982, can give inaccurate R/MIN readings when a tachometer generator or magnetic pickup is used on the MAG input at the same time that a 6V4950 Injection Line Speed Pickup is connected to the PHOTO input. Use the following procedure to correct this problem.

NOTE: Later multitachs that already have this modification can be identified by the letter "A" on the connector panel next to the power input connector as shown below.

1. Obtain a 220K Ohm (220,000 Ohm) ± 10%, 1/4 Watt carbon resistor from an electronic supply store.

2. Remove the rear cover and the printed circuit board from the multitach as shown on page 19.

3. Remove resistor R16 (1) by heating each lead wire with a small soldering iron until the solder melts; then use needle nose pliers or a 5P1720 Seal Pick to lift the resistor out of the printed circuit board.

4. Install the new 220K Ohm resistor in the location from which R16 resistor (1) was removed.

5. Raise R15 (2) approximately 1 mm (.04 in.) above the printed circuit board. Do this by heating the lead at each end of the resistor, and using a 5P1720 Seal Pick to lift the resistor after the solder melts.