Lambda LL Series Instruction Manual page 11

MAINTENANCE
GENERAL
This section describes trouble analysis routine, replacement procedures, cal-
ibration and test procedures that are useful for servicing the Lambda LL power sup-
ply. A trouble chart is provided as an aid for the troubleshooter. Refer to the
section on specifications and features for the minimum performance standards.
TROUBLE ANALYSIS
Whenever trouble occurs, systematically check fuse, primary power lines, ex-
ternal circuit elements, and external wiring for malfunction before trouble shoot-
ing the equipment. Failures and malfunctions often can be traced to simple causes
such as improper jumper and supply-load connections or fuse failure due to metal
fatigue.
Use the electrical schematic diagram and block diagram, figure 2, as an aid
to locating trouble causes. The schematic diagram contains various circuit volt-
ages that are averages for normal operation. Measure these voltages using the con-
ditions for measurement specified on the schematic diagram. Use measuring probes
carefully to avoid causing short circuits and damaging circuit components.
CHECKING TRANSISTORS AND CAPACITORS
Check transistors with an instrument that has a highly limited current capabil-
ity. Observe proper polarity to avoid error in measurement. The forward transistor
resistance is low but never zero; backward resistance is always higher than the
forward resistance.
For good transistors, the forward resistance for any junction is always
greater than zero.
Do not assume trouble is eliminated when only one part is replaced. This is
especially true when one transistor fails, causing other transistors to fail. Re-
placing only one transistor and turning power on, before checking for additional
defective components could damage the replaced component.
When soldering semi-conductor devices, wherever possible, hold the lead being
soldered with a pair of pliers placed between the component and the solder joint to
provide an effective heat sink.
NOTE: The leakage resistance obtained from a simple resistance
check of a capacitor is not always an indication of a faulty cap-
acitor. In all cases the capacitors are shunted with resistances,
some of which have low values. Only a dead short is a true indi-
cation of a shorted capacitor.
PRINTED CIRCUIT BOARD MAINTENANCE TECHNIQUES
T If foil is intact but not covered with solder it is a good contact. Do
not attempt to cover with solder.
2% Voltage measurements сап be made from either side of the board. Use а
needlepoint probe to penetrate to the wiring whenever a protective coating is used
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