DIGITAL MULTIMETER KIT MODEL M-1007K Assembly and Instruction Manual Elenco Electronics, Inc. ® Copyright © 2008 by Elenco® Electronics, Inc. All rights reserved. No part of this book shall be reproduced by any means; electronic, photocopying, or otherwise without written permission from the publisher.
PARTS LIST If you are a student, and any parts are missing or damaged, please see instructor or bookstore. If you purchased this meter kit from a distributor, catalog, etc., please contact Elenco® Electronics (address/phone/e-mail is at the back of this manual) for additional assistance, if needed. Qty. r1 r1 r1 r1 r1 r1 r1 r1 r1 r2 r3 r1 r6 r2 r1 r1 Symbol R10 R8 R20 R21 R5 R6 R22 R7 R23 R4, R30 R24, R25, R35 R1 R12-15, R18, R19 R26, R27 R2 R3 RESISTORS (Parts mounted on card.) Value Color Code .99Ω .
PARTS IDENTIFICATION Battery Snap Resistors PC Board with IC Transistor Socket LCD Assembly Zebra Clip/Zebra/LCD Zebra Clip Shunt Wire Selector Knob Potentiometer Fuse Clip Ball Bearing Slide Contact Zebra Fuse LCD Input Socket Springs Capacitors Diode C7 Mylar Discap IDENTIFYING RESISTOR VALUES Use the following information as a guide in properly identifying the value of resistors.
CONSTRUCTION Introduction • Tips should be cleaned frequently to remove oxidation before it becomes impossible to remove. Use Dry Tip Cleaner (Elenco® #SH-1025) or Tip Cleaner (Elenco® #TTC1). The most important factor in assembling your M-1007K Digital Multimeter Kit is good soldering techniques. Using the proper soldering iron is of prime importance. A small pencil type soldering iron of 25 - 40 watts is recommended. The tip of the iron must be kept clean at all times and well tinned.
ASSEMBLY INSTRUCTIONS Identify and install the following parts as shown. After soldering each part, mark a check þ in the box provided. Be sure that solder has not bridged to an adjacent pad. R15 - 220kΩ 5% 1/4W Resistor (red-red-yellow-gold) (see Figure A) R5 - 1kΩ 5% 1/4W Resistor (brown-black-red-gold) (see Figure A) C2 - .1μF (104) Mylar Cap. (small yellow) C7 - .1μF 63V Mylar Cap. (104 or 0.
ASSEMBLY INSTRUCTIONS Identify and install the following parts as shown. After soldering each part, mark a check þ in the box provided. Be sure that solder has not bridged to an adjacent pad. R32 - 2kΩ Thermistor PTC R21 - 900Ω .25% 1/4W Resistor (white-black-black-black-blue) (see Figure A) R20 - 100Ω .25% 1/4W Resistor (brown-black-black-black-blue) (see Figure A) D3 - 1N4007 Diode (see Fig. D) R22 - 9kΩ .25% 1/4W Resistor (white-black-black-brown-blue) (see Figure A) R8 - 9Ω .
r Remove the clear protective film from the front of the LCD as shown in Figure F. (Note: DO NOT remove the white backing on the other side of the LCD). r Insert the LCD into the case (the tab on the LCD must be in the same direction shown in Figure G). Be sure to insert the LCD under the tab on the case as shown and push the edge of the LCD against the raised area on the case. Press into place.
r Put the bearings into two opposite indents in the case top as shown in Figure K. r Place the six slide contactors on the selector knobs as shown in Figure K. r Place the selector knob into the case top so that the springs fit over the ball bearings as shown in Figure K. r Place the PC board over the selector knob. Be sure that the 8-pin socket slides into its hole. Then fasten the PC•board with three 6mm screws as shown in Figure K. r Insert the 0.5A, 250V fuse into the fuse clips.
TESTING, CALIBRATION, AND TROUBLESHOOTING TESTING OF LCD With no test leads connected to the meter, move the selector switch around the dial. You should obtain the following readings. A (–) sign may also be present or blinking. 1) ACV Range: 750 200 2) DCA,10A Ranges: 200μ 2m 20m 200m 10A HV 0 0 0 0 0.0 3) Ohms, Diode and hFE Ranges: B indicates blank. hFE 000 Diode ( ) 1BBB 200 1 B B.B 0 0.0 .0 0 0 0.0 0 0 0.0 0.0 0 2k 20k 200k 2M 4) DCV Range: 1.B B B 1 B.B B 1 B B.B 1.
DC VOLTS TEST 1) If you have a variable power supply, set the supply to about the midpoint of each of the DCV ranges and compare the kit meter reading to a meter known accuracy. 2) If you do not have a variable power supply, make the following two tests: a) Set the range switch to 2V and measure the voltage across the 100Ω resistor of Figure M. You should get about 820mV. Compare the reading to a meter of known accuracy.
RESISTANCE/DIODE TEST 1) Measure a resistor of about half of the full scale value of each resistance range. Compare the kit meter readings to those from a meter of known accuracy. 2) Measure the voltage drop of a good silicon diode. You should read about 700mV. Power diodes and the base to emitter junction of power transistors may read less. If any of these tests fail: a) Check the values and the soldering of resistors PTC - R2, R20 - R27, and R35.
THEORY OF OPERATION A block diagram of the M-1007K is shown in Figure 1. Operation centers around a custom LSI chip. This chip contains a dual slope A/D (analog to digital) converter, display latches, seven segment decoder and display drivers. A block diagram of the IC functions is shown in Figure 1. The input voltage or current signals are conditioned by the selector switches to produce an output DC voltage with a magnitude between 0 and 199mV.
The integrate period begins at the end of the autozero period. As the period begins, the AZ switch opens and the INTEG switch closes. This applies the unknown input voltage to the input of the A/D converter. The voltage is buffered and passed on to the integrator to determine the charge rate (slope) on the INTEG capacitor. At the end of the fixed integrate period, the capacitor is charged to a level proportional to the unknown input voltage.
a f a b g b e c d BACKPLANE 28 LCD PHASE DRIVER 7 Segment Decode 7 Segment Decode TYPICAL SEGMENT OUTPUT V+ 7 Segment Decode 200 0.5mA LATCH Segment Output 2mA Thousand Tens Hundreds Units Internal Digital Ground To Switch Drivers From Comparator Output V+ CLOCK 6.2V LOGIC CONTROL -4 * 3 TEST Internal Digital Ground 1V 500Ω * Three inverters. One inverter shown for clarity. 8 7 6 OSC 3 OSC 2 OSC 1 CREF CREF+ 42 V+ 44 43 A-Z & Z1 41 A-Z & Z1 1 + 2.
DC VOLTAGE MEASUREMENT 200mV Figure 4 shows a simplified diagram of the DC voltage measurement function. The input voltage divider resistors add up to 1 megaohm. Each step down divides the voltage by a factor of ten. The divider output must be within the range –0.199 to +0.199 volts or the overload indicator will function. The overload indication consists of a 1 in the most significant digit and blanks in the remaining digits.
RESISTANCE MEASUREMENT Figure 7 shows a simplified diagram of the resistance measurement function. A simple series circuit is formed by the voltage source, a reference resistor from the voltage divider (selected by the selector switches), and the test (unknown) resistor. The ratio of the two resistors is equal to the ratio of their respective voltage drops.
METER OPERATION PRECAUTIONS AND PREPARATIONS FOR MEASUREMENT 1) Be sure the battery is connected to the battery snap and correctly placed in the battery compartment. 2) Before connecting the test leads to the circuit, be sure the range switch is set to the correct position. 3) Be sure that the test leads are connected to the correct meter terminals before connecting them to the circuit. 4) Before changing the range switch, remove one of the test leads from the circuit.
RESISTANCE MEASUREMENTS 1) 2) 3) 4) Connect the black test lead to the “COM” terminal. Connect the red test lead to the “VΩmA” terminal. Set the range switch to the desired “Ω” position. If the resistance being measured is connected to a circuit, turn off the power to the circuit being tested and discharge all of the capacitors. 5) Connect the leads across the resistor to be measured and read the display. When measuring high resistance, be sure not to contact adjacent points even if insulated.
SCHEMATIC DIAGRAM -18-
Elenco® Electronics, Inc. 150 Carpenter Avenue Wheeling, IL 60090 (847) 541-3800 Website: www.elenco.com e-mail: elenco@elenco.
