Manual

30
1. The following instructions are for use by qualified
service personnel only. To avoid electrical shock, do
not perform servicing other than contained in the
operating instructions unless you are qualified to do so.
2. When the unit is plugged into an ac outlet, even if the
POWER ON switch is off, ac line voltage is present as
some input power circuits. Observe caution any time
the case is removed from the instrument.
PREVENTIVE MAINTENANCE
Do not overload the instrument. Excessive output current can
damage the variable auto-transformer. Prolonged use at high
current accelerates failure. Keep output current as low as
possible, and never exceed the maximum rating of the unit. If
possible, power only one piece of equipment at a time. Use the
ISOLATED OUTPUT only for the equipment under test-not for
other test equipment. It is very important to observe the
maximum current derating (Table 1) above 130 volts, and to
allow sufficient cooling time when operating Model 1655A at
greater than 3 amps outlet.
Periodic inspection of the brush on the variable contact of the
auto-transformer is recommended. Badly worn or arcing brushes
should be replaced. See the AUTO-TRANSFORMER BRUSH
REPLACEMENT paragraph for replacement procedures.
RETURNING FOR SERVICE
If you have encountered a problem with your unit and choose
to return it for service, check the following before returning.
1. Is the circuit breaker reset (Model 1655A)? See FUSE
REPLACEMENT paragraph below if required.
2. Are the fuses okay? See FUSE REPLACEMENT
paragraph below if required.
FUSE REPLACEMENT
The ac power supply will trip its circuit breaker or blow a fuse
only if it is severely overloaded or a failure occurs in the
instrument. Always turn off the unit to reset the circuit breaker or
replace a fuse. If fuses are internal, unplug the instrument from
its wall outlet before attempting replacement. Before turning the
unit back on, reduce the output voltage or remove the overload
that caused the blown fuse. Replace the fuse only with the
original type and value-never one of a large value. A larger value
may create a fire and safety hazard, or cause serious damage to
the equipment. Also refer to the following specific fuse
replacement information for each model.
Model 1653A
If the instrument is severely overloaded at higher output
voltages, fuse F1 on the rear panel will blow. The unit will stop
operating and the pilot light will go off. If the instrument is
severely overloaded at low output voltage, internal fuse F2 will
blow. In this case, there will be no output but the pilot light will
stay on. Fig. 14 shows the location of the fuses. Replace fuse F1
only with a 3-amp slow-blow type 3AG.
MAINTENANCE AND CALIBRATION
WARNING