Hameg HM303-6 Manual

Also see for HM303-6: Operator's manual Service manual

Contents

17Subject to change without noticeFig. 1 shows a case where the HOLD OFF knob is in the minimumposition and various different waveforms are overlapped on thescreen, making the signal observation unsuccessful.Fig. 2 shows a case where only the desired parts of the signal arestably displayed.Component TesterGeneralThe HM303-6 has a built-in electronic Component Tester(COMP. TESTER), which is used for instant display of a testpattern to indicate whether or not components are faulty. TheCOMP. TESTER can be used for quick checks of se-miconductors (e.g. diodes and transistors), resistors,capacitors, and inductors. Certain tests can also be made tointegrated circuits. All these components can be tested in andout of circuit.The test principle is fascinatingly simple. A built-in generatordelivers a sine voltage, which is applied across the componentunder test and a built-in fixed resistor. The sine voltage across thetest object is used for the horizontal deflection, and the voltagedrop across the resistor (i.e. current through test object) is usedfor vertical deflection of the oscilloscope. The test pattern showsa current-voltage characteristic of the test object.Since this circuit operates with a frequency of 50Hz (±10%)and a voltage of approx. 7Vrms (open circuit), the indicatingrange of the component tester is limited. The impedance ofthe component under test is limited to a range from 20Ω to4.7kΩ. Below and above these values, the test pattern showsonly short-circuit or open-circuit. For the interpretation of thedisplayed test pattern, these limits should always be borne inmind. However, most electronic components can normally betested without any restriction.Using the Component TesterThe component tester is switched on by depressing theCOMP. TESTER pushbutton (on) beneath the screen. Thismakes the vertical preamplifier and the time base generatorinoperative. A shortened horizontal trace will be observed. Itis not necessary to disconnect scope input cables unless in-circuit measurements are to be carried out. In the COMP.TESTER mode, the only controls which can be operated areINTENS, FOCUS, X-POS. and X-MAG. X10 pushbutton(must be released). All other controls and settings have noinfluence on the test operation.For the component connection, two simple test leads with4mm Ø banana plugs, and with test prod, alligator clip orsprung hook, are required. The test leads are connected to theinsulated socket and the adjacent ground socket beneath thescreen. The component can be connected to the test leadseither way round.After use, to return the oscilloscope to normal operation,release the COMP. TESTER pushbutton (off).Test ProcedureCaution!Do not test any component in live circuitry - remove allgrounds, power and signals connected to the componentunder test. Set up Component Tester as stated above.Connect test leads across component to be tested.Observe oscilloscope display.Only discharged capacitors should be tested!Test Pattern Displays• Open circuit is indicated by a straight horizontal line.• Short circuit is shown by a straight vertical line.Testing ResistorsIf the test object has a linear ohmic resistance, both deflectingvoltages are in the same phase. The test pattern expected froma resistor is therefore a sloping straight line. The angle of slopeis determined by the resistance of the resistor under test. Withhigh values of resistance, the slope will tend towards thehorizontal axis, and with low values, the slope will movetowards the vertical axis.Values of resistance from 20ΩΩΩΩΩ to 4.7kΩΩΩΩΩ can be approximatelyevaluated. The determination of actual values will come withexperience, or by direct comparison with a component of aknown value.Testing Capacitors and InductorsCapacitors and inductors cause a phase difference betweencurrent and voltage, and therefore between the X and Ydeflection, giving an ellipse-shaped display. The position andopening width of the ellipse will vary according to the impedancevalue (at 50Hz) of the component under test.A horizontal ellipse indicates a high impedance or a relativelysmall capacitance or a relatively high inductance.A vertical ellipse indicates a small impedance or a relativelylarge capacitance or a relatively small inductance.A sloping ellipse means that the component has aconsiderable ohmic resistance in addition to its reac-tance.The values of capacitance of normal or electrolytic capacitorsfrom 0.1μF to 1000μF can be displayed and approximate valuesobtained. More precise measurement can be obtained in asmaller range by comparing the capacitor under test with acapacitor of known value. Inductive components (coils,transformers) can also be tested. The determination of thevalue of inductance needs some experience, because inductorshave usually a higher ohmic series resistance. However, theimpedance value (at 50Hz) of an inductor in the range from 20Ωto 4.7kΩ can easily be obtained or compared.Component Tester