
HP5501B
Service
8-44
8-146. Power Amplifier Troubleshooting
8-147. The heart of the power amplifier is A3U20, a fixed-frequency pulse-width-modulator control unit.
The IC operates at a fixed frequency set by A3R63 and C38. The outputs are used to control the
amount of ±1SV current supplied to the laser assembly during the warmup and optical modes of
operation. To troubleshoot the power amp, theory of operation, schematics diagrams and
waveforms, and the following procedure have been provided.
a.
Set HTR OK jumper to HI, ~REF ON to La and wait for READY LED to stay on. Set
POWER AMP jumper to UP. Remove HEATER jumper. Is voltage at U13 (Pin 3)
approximately 0.1V? If not, check A3R27, R31, R49, R50, R51, C18, and U13. If so, go to
step b.
b.
Within 1 minute of setting POWER AMP to UP, is voltage at A3TP11 a nonsymmetrical
square wave with ±peak voltages >13 Volts? (See
Figure
8-20.) If yes, go to step d. If
not, go to step c.
NOTE
Figure 8-20 oscilloscope settings are as follows:
Time/Division: 10 microseconds/division
Volts/Division: 5 Volts/division
Coupling: DC
Figure 8-20. Test Point 11 Waveform (HEATER SENSE)
c.
Is U13 (Pin 6) > +13 Vdc? If yes, go to step j. If no, check feedback path through R6SB,
C20, and R32, or replace U13.
d.
Set POWER AMP jumper to DWN. Is voltage at A3TP11 <0.6 Vdc within 1 minute? If yes,
go to step g. If no, go to step e.
Содержание 5501B
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Страница 111: ...HP5501B Service 8 51 Figure 8 23 A1 Connector Board Component Schematic Diagram ...
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