User manual

ManualsBrandsROHDE & SCHWARZ ManualsLaboratory Test EquipmentDigital HMO 1024 100 MHz 12-channel 1 null 1 null 8 Bit Digital storage (DSO), Mixed signal (MSO), Spec

Analysis

ting to the conducting state will be indicated in their charac-

teristic. As far as is possible with the available voltages and

currents the forward and backward characteristics are dis-

played (e.g. with zener diodes up to 9 V). Because this is a

two-pole measurement, the gain of a transistor can not be

determined, however, the B-C, B-E, C-E diodes can be mea-

sured. With this exception the diodes can be measured wi-

thout fear of destruction as the maximum voltage is limi-

ted to 9 V and the current to a few mA. This implies, howe-

ver, that a measurement of breakdown voltages > 9 V is not

possible. In general this is no disadvantage because, if there

is a defect in a circuit, gross deviations are to be expected

which will point to the defective component. Rather exact

results may be achieved if the measurements are compared

to those of intact components. This is especially true for se-

miconductors. The polarity of diodes or transistors can thus

beidentiediftheletteringormarkingismissing.Please

note that with semiconductors changing the polarity will

cause the display to rotate 180 degrees around the screen

center. More important in practice is the quick determina-

tion of plain shorts and opens which are the most common

causes of requiring service.

Please note that with semiconductors changing the pola-

rity (e.g. by exchanging the COMP.TESTER and ground ter-

minals) will cause the display to rotate 180 degrees around

the screen center. More important in practice is the quick

determination of plain shorts and opens which are the

most common causes of requiring service.

9.5.2 In-circuit tests

They are possible in many cases but deliver rarely clear re-

sults. By paralleling of real or complex impedances – es-

pecially if those are fairly low impedance at 50 Hz/200 Hz

– there will be mostly great differences compared to indi-

vidual components. If circuits of the same type have to be

tested often (service), comparisons with intact circuits may

help again. This is also quickly done because the intact cir-

cuit has not to be functional, also it should not be ener-

gized. Just probe the various test points with the cables

of the component tester of the unit under test and the in-

tact unit and compare the screen displays. Sometimes the

unit under test may already contain an intact portion of the

same type, this ist e.g. the case with stereo circuits, push-

pull circuits or symmetrical bridge circuits. In cases of doubt

one side of the dubious component can be unsoldered and

this free contact should be connected to the COMP.TES-

TERcontactwhichisnotidentiedasthegroundcontact.

This will reduce hum pick-up. The contact with the ground

symbol is connected to the scope chassis and is thus not

susceptible to hum pick-up.

It is highly recommended to observe the necessary precautions

when handling MOS components which can be destroyed by sta-

tic charges and even tribo electricity.

Like mentioned in the chapter Safety, all measurement connec-

tors as well as COMP.TESTER contacts are connected to the

mains safety earth (in proper operation). As long as individual

components are tested, this has no consequences because these

components are not connected to the mains safety earth.

Fig. 9.11: Excamples of Component test