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39/41B
Service Manual
5-9.
Troubleshooting the Range Control Circuit
The Tester's measurement range can be changed manually or automatically. If the Tester
is unable to change ranges, proceed with the following steps:
1. Check for the correct level at U1-12 through U1-18 by placing the instrument in
Range
20V, 50V, 100V, and 200V
500V
1000V
2A, 5A, 10A, and 20A
50A, 100A, and 200A
500A, 1000A, and 2000A
"1" = Logic High (> 0.2V) and "0" = Logic Low (< 0.8V)
2. If the latches are correctly written, there is a problem somewhere in the analog input
3. If latch (U1) is not written properly, verify that CS_GAIN* from U3-18 occurs when
5-10
in Chapter 7. If the row line is driven low for an incorrect column line, then there is
some external problem, possibly a keypad or elastomeric interconnect problem.
manual range and verifying that the input latch is set to the values in Table 5-3.
Table 5-3. Latch Signals for Voltage Ranges
U1-12
1
1
0
N/A
N/A
N/A
circuits. Refer to the analog theory for troubleshooting assistance.
a range change is attempted. Also, the data should be on the appropriate latch input
pins to be latched into the latch. If the CS_GAIN* pulse is not generated, verify that
all of the correct signals are correctly feeding U3 (A15, A14, A5, A4, RD, WR, XY,
PS). If they are correctly feeding, and you still do not have a correct CS_GAIN*
signal, U3 may be defective. Alternatively, if the CS_GAIN* signal is present to the
U1 latch but the correct data is not getting latched, verify that the data bus feeding
the latch contains the correct data on the rising edge of the CS_GAIN* pulse. If the
data bus does contain the correct data on the rising edge of CS_GAIN* but the data
is not getting latched, there is probably a defective latch (U1).
U1-13
U1-14
U1-15
1
0
N/A
0
1
N/A
1
1
N/A
N/A
N/A
1
N/A
N/A
1
N/A
N/A
0
U1-16
U1-17
U1-18
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0
1
0
0
0
1
1
0
1
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Troubleshooting
