Service manual

If the unit has failed selftest by reporting an error 105-108 at turn-on and no problem can be found using SA, the IMON

adjustment may be at fault. Refer to ''POST REPAIR CALIBRATION" and perform the IMON Adjustment.

Also, check if the switches in U309 are operating properly. Turn off the SA mode by removing the jumpers. Now check

test points

and using the measurement conditions specified in Table 3-3. A switch should close when the

applicable test point is a Low level. If the switches are operating properly, check test points

( - IMON), (-10V),

and ( - VMON)

If all signatures and test points check out, the DAC or amplifier that is generating the incorrect waveform is probably faulty.

Slew Circuit Troubleshooting (Figure 3-4)

This circuit consists primarily of three operational amplifier stages (U306 and U307) and four analog switches (U346). The

four switches determine the slew rate by selecting loop gain and response time combinations. The switches are controlled

by the SLW1-SLW4 signals to provide 12 slew rates.

To troubleshoot the slew circuit, 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 SA waveforms at the top of Figure 3-4 can only be generated

when the SA mode is on. If the SA waveforms are incorrect, check the SDB0-7 data inputs to U305 and the SLW signal

outputs from U305 using SA Table 3-13. If the signatures are correct, an amplifier or switch is probably defective.

The waveforms at the bottom of Figure 3-4 are generated when various slew rates are programmed. These waveforms

check the operation of the slew circuit switches (U317). They are not generated in the SA mode. To generate these

waveforms, turn the SA mode off (remove jumpers) and program 3 different slew rates ( .001, 0.5 and 2.5 A/µs) from the

front panel as shown in the following sequence. Use a scope with delayed sweep to verify the waveforms shown for slew

rate in Figure 3-4.

MODE = CURR

CURR = 5

Tran Level = 10

Freq = 80

Dcycle = 50

Tran on/off = on

Slew = .001 (Slew Rate #1) | 60502A

Slew = .5 (Slew Rate #9) | only

Slew = 2.5 (Slew Rate #11) |

The three slew rates programmed from the front panel toggle all four switches in the slew circuit. Refer to the following

table if you need to check the state of the switches for a specific slew rate. Remember that the front panel is programmed in

microseconds. Note that when the SLW signal is LO, the switch it closed; when the SLW signal is HI, the switch is open.

If the slew rate tests check out, and a problem still exists, troubleshoot the CC/CV control circuits as described in the next

section.