9. If the instrument is working but the HP-IB is not, replace U403
and U404.
Troubleshooting the A3 Power Supply Board
Warning
High voltage (more than 500 Volts) is present when the shield is
removed trom the A3 power supply board or when the board is
operated separately.
Preparing to Check Power Supply Voltages
1. Make sure that the power cord is disconnected and remove the
instrument housing (see "Removing the Instrument Housing"
in
Chapter 3).
2. Remove the safety shield from the power supply board and fasten
the power supply board with 2 screws again.
Warning
When measuring the DC Voltages be aware of the high voltage which
is present on this board.
If you are operating the power supply board outside the instrument,
a variable isolating transformer must be used. In this case it is
recommended that you use a mains voltage of 110 Volts during
troubleshooting.
As the switching circuit is controlled from the +5 Volt supply, it is
useful to load the +5 Volt supply. If you are operating the power
supply board outside the instrument, approximately 9n (for example,
4x2.2n (P /N 0812-0039) in series) connected between +5V and
ground is sufficient. +5V can be found on A3 J300 pin 14, 15, or 16.
Ground can be found on A3 J300 pin 3, 5, 6, 8, lO, 11, 12, or 13.
The DC voltages can be checked without this load but the waveforms
in the switching circuit are distorted.
Checking Power Supply Voltages
Warning
The primary supply is floating .
• Connect the oscilloscope with lO to 1 probe to A3 R124 (Gate of
A3 Q101) and GND A3 C115/R124.
The signal at Q101/2 should be as follows:
Amplitude -0.5 Volt to +8 Volt
Period
7.2JLs
4-2 Troubleshooting
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