Tektronix 556 Instruction Manual page 93

Maintenance— Type 556
ment transistor or tube might also be damaged. If substitute
transistors or tubes are not available, a dynamic tester may
be used (such as Tektronix Type 570 or 575). Static type
testers are not recommended, however, since they do not
check operation under simulated operating conditions.
Two small access plates have been provided inside
each plug in com partm ent to a llo w easy inspection
or replacem ent o f the A and B Sweep G e nera tor
tubes V 625 and V 825.
CAUTION
Care should be exercised w hen re p la cin g plastic-
cased transistors, as tw o types o f lead c o n fig u ra ­
tions are m anufactured. If in d o u b t as to the co r­
rect lead nom enclature, refer to the m anufacturer's
basing diagram s. Some transistors have the lead
code (E,B,C) marked on the case.
sockets in this instrum ent are w ired fo r the lead
c o n fig u ra tio n used in m etal-cased transistors.
Diodes. A diode (excluding the tunnel diodes, zener diodes
and the silicon diodes in the CRT circuit) usually can be
checked for an open or shorted condition by measuring the
resistance between terminals. W ith an ohmmeter scale hav­
ing an internal source of about 1.5 volts, the resistance should
4-12
NOTE
A ll transistor
be very high in one direction and very low when the leads are
reversed.
Do not use an ohmm eter scale th a t has a high
in te rn a l current.
diode. Do not measure tunnel diodes w ith an ohm ­
meter; use a dynam ic tester
Type 575 Transistor-Curve T ra ce r).
Resistors. Resistors can be checked with an ohmmeter.
Check the Electrical Parts List for the tolerance o f the resis­
tors used in this instrument. Resistors normally do not need
to be replaced unless the measured value varies widely from
the specified value.
Inductors. Check for open inductors by checking con­
tinuity with an ohmmeter. Shorted or partially shorted induc­
tors can usually be found by checking the waveform response
when high-frequency signals are passed through the circuit.
Partial shorting often reduces high-frequency response (roll­
off).
Capacitors. A leaky or shorted capacitor can best be
detected by checking resistance with an ohmmeter on the
highest scale. Do not exceed the voltage rating of the capac­
itor. The resistance reading should be high after initial
charge of the capacitor.
detected with a capacitance meter or by checking whether
the capacitor passes AC signals.
NOTES
CAUTION
High currents may dam age the
(such as Tektronix
An open capacitor can best be