Danfoss VLT HVAC FC 100, Service Manual, Page: 102 / 220

6.2.4 Soft Charge Rectifier Test: E-frame Size
The DC cable at connector MK3 remains disconnected for this procedure.
Since the rectifier test requires the soft charge resistor to be in the circuit, verify the resistor is
good before proceeding.
1. Measure the resistance between pins A and B of connector MK4 on the soft charge
card. It should read 27 ohms (
±
10%) for 380–500 V adjustable frequency drives or 68
ohms ( ± 10%) for 525–690 V adjustable frequency drives. A reading outside this range
indicates a defective soft charge resistor. Replace the resistor according to the disas-
sembly procedures in Section 8. Continue tests.
Should the resistor be defective and a replacement not readily available, the remainder of the
tests can be carried out by disconnecting the cable at connector MK4 on the soft charge card and
placing a temporary jumper across pins A and B. This provides a path for continuity for the re-
maining tests. Ensure any temporary jumpers are removed at the conclusion of the tests.
For the following tests, set the meter to diode check or Rx100 scale.
2. Connect the negative (-) meter lead to the positive (+) MK3 (A) (DC output to DC
bus), and connect the positive (+) meter lead to MK1 terminals R, S, and T in sequence.
Each reading should show a diode drop.
3. Reverse meter leads with the positive (+) meter lead to the positive (+) MK3 (A).
Connect the negative (-) lead to MK1 terminals R, S, and T in sequence. Each reading
should show open.
4. Connect the positive (+) meter lead to the negative (-) MK3 (C). Connect the negative
(-) meter lead to MK1 terminals R, S, and T in sequence. Each reading should show a
diode drop.
5. Reverse the meter leads with the negative (-) meter lead to the negative (-) MK3 (C).
Connect the positive (+) meter lead to MK1 terminals R, S, and T in sequence. Each
reading should show open.
An incorrect reading here indicates the soft charge rectifier is faulty. The rectifier is not serviced
as a component. Replace the entire soft charge card in accordance with the disassembly proce-
dures in Section 8.
Reconnect the MK3 on the soft charge card after these tests.
380–480/500V: Blue MOV and 8 PTCs.
525–690 V: Red MOV and 6 PTCs.
1 MK1 3 MK4
2 MK3 4 MK2
130BX120.10
1
2
3
4
Figure 6.9: Soft Charge Card Connectors
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives 6 Test Procedures
MG.90.L1.22 - VLT ® is a registered Danfoss trademark
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