Hameg HM303-6 Manual

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

Contents

18 Subject to change without noticeTesting SemiconductorsMost semiconductor devices, such as diodes, Z-diodes,transistors, FETs can be tested. The test pattern displays varyaccording to the component type as shown in the figuresbelow.The main characteristic displayed during semiconductor testingis the voltage dependent knee caused by the junction changingfrom the conducting state to the non conducting state. Itshould be noted that both the forward and the reversecharacteristic are displayed simultaneously. This is a two-terminal test, therefore testing of transistor amplification isnot possible, but testing of a single junction is easily andquickly possible. Since the test voltage applied is only verylow, all sections of most semiconductors can be testedwithout damage. However, checking the breakdown or reversevoltage of high voltage semiconductors is not possible. Moreimportant is testing components for open or short-circuit,which from experience is most frequently needed.Testing DiodesDiodes normally show at least their knee in the forwardcharacteristic. This is not valid for some high voltage diodetypes, because they contain a series connection of severaldiodes. Possibly only a small portion of the knee is visible. Z-diodes always show their forward knee and, up to approx. 9V,their Z-breakdown, forms a second knee in the oppositedirection. A Z-breakdown voltage of more than approx. 9V cannot be displayed.The polarity of an unknown diode can be identified bycomparison with a known diode.Testing TransistorsThree different tests can be made to transistors: base-emitter,base-collector and emitter-collector. The resulting test patternsare shown below.The basic equivalent circuit of a transistor is a Z-diode betweenbase and emitter and a normal diode with reverse polaritybetween base and collector in series connection. There arethree different test patterns:For a transistor the figures b-e and b-c are important. Thefigure e-c can vary; but a vertical line only shows short circuitcondition.These transistor test patterns are valid in most cases, butthere are exceptions (e.g. Darlington, FETs). With the COMP.TESTER, the distinction between a P-N-P and an N-P-Ntransistor is discernible. In case of doubt, comparison with aknown type is helpful. It should be noted that the same socketconnection (COMP. TESTER or ground) for the same terminalis then absolutely necessary. A connection inversion effectsa rotation of the test pattern by 180 degrees round about thecenter point of the scope graticule.Pay attention to the usual caution with single MOS-components relating to static discharge or frictionalelectricity!In-Circuit TestsThe test patterns show some typical displays for in-circuittests.Caution!During in-circuit tests make sure the circuit is dead. Nopower from mains/line or battery and no signal inputsare permitted. Remove all ground connections includingSafety Earth (pull out power plug from outlet). Removeall measuring cables including probes betweenoscilloscope and circuit under test. Otherwise bothCOMP. TESTER leads are not isolated against the circuitunder test.Component Tester