Service manual

102 Replaces page 42
SLEW RATE SWITCH SETTINGS
Refer to Module Operating Manual for Slew Rate Steps
Slew Rate SLW1 SLW2 SLW3 SLW4
#1
HI HI LO HI
#2
HI LO LO HI
#3
LO HI LO HI
#4
HI HI HI HI
#5
HI LO HI HI
#6
LO HI HI HI
#7
HI HI LO LO
#8
HI LO LO LO
#9
LO HI LO LO
#10
HI HI HI LO
#11
HI LO HI LO
#12
LO HI HI LO
CC/CV Control Circuit Troubleshooting (Figure 3-5)
Depending upon which operating mode (and range in the CR mode) is selected, either the CC or the CV loop controls the
conduction of the input power stages. If the CC or CR (middle and high ranges only) mode is selected, the
CC EN_ signal
goes low connecting the SLEW signal to the CC control circuit (U308, U16). If the CV or CR (low range only) mode is
selected, the
CV EN_ signal goes low connecting the SLEW signal to the CV control circuit (U308, U13).
The overvoltage (OV) circuit (U17, D17) is also shown on Figure 3-5. When an OV condition is detected, the OV circuit
generates a negative signal via diode D17 which causes the input power stages to increase current flow in order to limit the
input voltage. The OV condition is detected when the input voltage exceeds 75V. When activated the OV circuit takes
control from the CC or CV control circuit.
To troubleshoot the CV or CC circuits, place the Electronic Load in the SA mode by connecting the jumpers in test headers
TP201 and TP301 in the SA mode positions (see Figure 3-2). The waveforms shown in Figure 3-5 can only be generated
when SA mode is on. If the waveforms are correct but a problem exits, troubleshoot the input power stages as described in
the next section.
If the waveforms are incorrect, turn off the SA mode (remove jumpers) and check that the CC and CV switches in U340 are
operating properly. If the
CC EN_ or CV EN_ input is LO, the applicable switch should be closed. You can use SA
Table 3-10 to check the
CC EN_ and CV EN_ signals. Next, check test points through using the measurement
conditions specified in Table 3-3. Also, check test points
( - VMON), ( - IMON), and ( + 12V ref).
If both the CC and CV control loops have problems, there may be another circuit affecting the CC and CV circuits.
Troubleshoot the input power stages, current limit, and power limit circuits as described in subsequent sections.