Hameg HM304 Manual

Hameg HM304 Manual Manual pdf 25 page image

25Subject to change without noticemid position (i.e. 20μs/div.). Prior to the commencement ofany check set the time variable control to CAL. The X-MAG.x10 LED should not light. This condition should be maintaineduntil the variation ranges of these controls are checked.Check that the sweep runs from the left to the right side ofthe screen (TIME/DIV. setting to 0.1s/div.; X-POS. control inmid-range). This check is only necessary after changing thecathode-ray tube.If a precise marker signal is not available for checking theTimebase time coefficients, then an accurate sine-wavegenerator may be used. Its frequency tolerance should notbe greater than ±1%. The timebase accuracy of the HM304is given as ±3%, but it is considerably better than this. Forthe simultaneous checking of timebase linearity and accuracyat least 10 oscillations, i.e. 1 cycle every div., should alwaysbe displayed. For precise determination, set the peak of thefirst marker or cycle peak exactly behind the first verticalgraticule line using the X-POS. control. Deviation tendenciescan be noted after some of the marker or cycle peaks.If a precise Time Mark Generator is used for checking, Nor-mal Triggering (NM LED lights) and TRIG. LEVEL controladjustment is recommended.The following table shows which frequencies are requiredfor the particular ranges.0.5s/div. - 2Hz 0.1ms/div. - 10kHz0.2s/div. - 5Hz 50μs/div. - 20kHz0.1s/div. - 10Hz 20μs/div. - 50kHz50ms/div. - 20Hz 10μs/div. - 100kHz20ms/div. - 50Hz 5μs/div. - 200kHz10ms/div. - 100Hz 2μs/div. - 500kHz5ms/div. - 200Hz 1μs/div. - 1MHz2ms/div. - 500Hz 0.5μs/div. - 2MHz1ms/div. - 1kHz 0.2μs/div. - 5MHz0.5ms/div. - 2kHz 0.1μs/div. - 10MHz0.2ms/div. - 5kHz 0.05μs/div. - 20MHzWhen the X-MAG. x10 function is active, a marker or cyclepeak will be displayed every 10div. ±5% (with variable controlin CAL. position; measurement in the 5μs/div. range). Thetolerance is better measurable in the 50μs/div. range (onecycle every 1div.).Holdoff timeThe variation of the holdoff time while turning the HOLD OFFknob can not be tested without opening the instrument.However, a visual check can be made if the instrument is notoperated in DELAY mode.Without an input signal, set TIME/DIV. to 0.05μs/div and timevariable control cw, use automatic peak (value) triggering. Atthe left hand stop of the HOLDOFF knob, the trace shouldbe bright. It should noticeably darken at the right hand stopof the HOLDOFF knob.Component TesterAfter selecting component tester mode by pressing theCOMP. TESTER button, a horizontal straight line shouldappear immediately, when the COMP. TESTER socket is open.The length of this trace should be approx. 8div if the X MAG.x10 LED is dark. With connection of the COMP. TESTERsocket to the ground jack in the Y-Section, a vertical straightline with approx. 6div. height should be displayed. The abovestated measurements have some tolerances.Trace AlignmentThe CRT has an admissible angular deviation ±5° betweenthe X deflection plane D1-D2 and the horizontal center line ofthe internal graticule. This deviation, due to tube productiontolerances (and only important after changing the CRT), andalso the influence of the earths magnetic field, which isdependent on the instruments North orientation, arecorrected by means of the TR potentiometer. In general, thetrace rotation range is asymmetric. It should be checked,whether the baseline can be adjusted somewhat sloping toboth sides round about the horizontal center line of thegraticule. With the HM304 in its closed case, an angle ofrotation ±0.57° (0.1div. difference in elevation per 10div.graticule length) is sufficient for the compensation of theearths magnetic field.Service InstructionsGeneralThe following instructions are intended as an aid for theelectronic technician, who is carrying out readjustments onthe HM304, if the nominal values do not meet thespecifications. These instructions primarily refer to thosefaults, which were found after using the Test Instructions.However, this work should only be carried out by properlyqualified personnel. For any further technical information callor write to HAMEG. Addresses are provided at the back ofthe manual. It is recommended to use only the original packingmaterial, should the instrument be shipped to for service orrepair (see also Warranty).Instrument Case RemovalThe rear cover can be taken off after unplugging the powercords triple-contact connector and after two nuts the washershave been removed. If a cross recessed pan head screw ispresent on the bottom of the instrument, it must be removedtoo. While the instrument case is firmly held, the entirechassis with its front panel can withdrawn forward. Whenthe chassis is inserted into the case later on, it should benoticed that the case has to fit under the flange of the frontpanel. The same applies for the rear of the case, on whichthe rear cover is put.Caution!During opening or closing of the case, the instrumentmust be disconnected from all power sources formaintenance work or a change of parts or components.If a measurement, trouble-shooting, or an adjustmentis unavoidable, this work must be done by a specialist,who is familiar with the risk involved.When the instrument is set into operation after the case hasbeen removed, attention must be paid to the accelerationvoltage for the CRT -2025V and to the operating voltages forboth final amplifier stages 175V and 144V. Potentials of thesevoltages are on the PS-Board, the CRT-PCB, on the upperand lower PCBs. Such potentials are moreover on thecheckpoint strips on the upper and lower horizontal PCBs.They are highly dangerous and therefore precautions mustbe taken. It should be noted furthermore that shorts occuringon different points of the CRT high voltage and unblankingcircuitry will definitely damage some semiconductors and theopto-coupler. For the same reason it is very risky to connectcapacitors to these points while the instrument is on.Capacitors in the instrument may still be charged, even whenthe instrument is disconnected from all voltage sources.Normally, the capacitors are discharged approx. 6 secondsafter switching off. However, with a defective instrument aninterruption of the load is not impossible. Therefore, afterswitching off, it is recommended to connect one by one allterminals of the check strips on the upper PCB across 1kΩto ground (chassis) for a period of 1 second.