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Diagnostic Testing and Troubleshooting (2635A)
Analog Troubleshooting
5A
5A-17
Table 5A-4. DC Volts HI Troubleshooting (2635A)
Checkpoint Signal Description Possible Fault
A3R11 HI Input A3K1 through A3K14, A3U4, A3U5, A3U11, A3U12,
A3L1, A3L2, A3L3
A3U8 pin 23 Input A3R11, A3K17, A3R42, A3C32
A3U8 pin 58 Input, DC filter output A3U8, A3Q2
5A-12. AC Volts Troubleshooting
Setup the instrument to measure a channel on the 300 mV ac range, and apply a signal to
that channel. Then trace this HI signal (referenced to the input channel LO terminal) as
described in Table 5A-5.
If the input HI path traces out properly, remove the input from the channel, and trace
continuity through the LO path. Check among A3L4 through A3L24, A3K1 through
A3K14, A3R43, A3R34, A3K16, and A3U8 pin 13.
Table 5A-5. AC Volts HI Troubleshooting (2635A)
Checkpoint Signal Description Possible Fault
A3R11 HI Input A3K1 through A3K14, A3U4, A3U5, A3U11, A3U12
A3L1, A3L2, A3L3
A3Z3 pin 1 Input A3R11, A3C31, A3K15
A3U6 pin 13 Amplified (X 2.5) input A3U7, A3Z3, A3Q3 through A3Q9, A3C15, A3C16,
A3R24, A3A25, A3R26, A3R27, A3R28, A3C23,
A3U6, A3Q13, A3U8
A3Z1 pin 2 DC equivalent of original input A3Z1, A3U8, A3R20, A3C6, A3C7, A3C10, A3R16,
A3R17
A3U8 pin 61 DC equivalent of original input A3Z1, A3U8, A3R20, A3C6, A3C7, A3C10, A3R16,
A3R17
5A-13. Ohms Troubleshooting
Setup a channel with an open input for the desired ohms range and place the instrument
in monitor mode on that channel. Use a meter with high input impedance to measure the
open-circuit voltage at the channel input for the ohms range as listed in Table 5A-6. If a
high input impedance meter is not available, only the 30-kΩ and lower ranges can be
checked.
If the proper voltage is not measured, setup a channel on the 300Ω range (open input),
and have the instrument monitor that channel. Check for 3V dc with respect to A3TP9,
and work through the HI SOURCE and HI SENSE paths as described in Table 5A-7.
If the HI path works correctly, trace continuity through the LO path. Check among A3L4
through A3L24, A3K1 through A3K14, A3R35, A3U8 pin 11, A3R43, A3K16, A3R34,
and A3U8 pin 13.