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Model 5501A
Maintenance
g. Remove beam obstruction (inserted in step a).
h. Depress RETUNE pushbutton. Proper indications are:
1) RETUNE FAILURE indicator extinguishes immediately.
2) RETUNE indicator goes out nine seconds after switch is depressed.
4-24. PHOTODIODE OFFSET ADJUSTMENT. This adjustment must be performed when the Lock Refer-
ence Board Assembly is replaced. The HP 5300/5306 (2 MHz frequency counter capability) or equivalent is
recommended. (An oscilloscope can also be used to measure the 2 MHz signal by expanding the horizontal
scale.)
4-25.
Make the adjustment according. to the following procedure (refer to Figure 4-4):
a.
Connect counter probe to A5TP6.
b. Adjust A5R4 for maximum frequency (or minimum period if an oscilloscope is used).
4-26.
Laser Tube Current Adjustment
4-27. Although all laser tubes appear to be identical, each has a slightly different current rating. Adjusting
the laser current regulator circuits for the correct current ensuresoptimum tube operation and output beam
bandwidth.
4-28.
Perform the laser current adjustment when the laser tube i s operating improperly (i.e., flashing on
and off) or when any of the following are replaced:
A1 Connector Board Assembly
A2 High Voltage Power Supply Assembly
A3 Laser Tube Assembly
A1 chassis-mounted series regulator
4-29. Recommended Test Equipment:
HP 5300/5306 Multimeter/Counter (dc voltage measurement)
4-30. This procedure is performed by adjusting the current regulator circuit while monitoring voltage
across the laser tube cathode resistor, AIR16 (refer to Figure 4-6). The regulator circuits and the cathode
resistor are mounted on the A1 Connector Board Assembly.Thevoltage across the 390-ohm cathode resistor
is determined by the laser tube current. Therefore the correct voltage i s calculated by multiplying the rated
tube current by 390. Adjust current a s follows:
NOTE
Since the laser head covers are removed, the safety switch, A1S2
(located on the connector board), must be actuated for the laser
current circuits to operate.
a.
Read the rated current stamped on the tube plate (this value is typically 2.6 mA to 5.1 mA).
b. Multiply this value by 390 (calculated value is typically 1.0 to 2.0 volts).
c. While monitoring the laser current test point, adjustthe laser current potentiometer, AlRl1,for the
value obtained in step b.
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