3. Insert the signal test board into power card connector MK104.
4. Check the SCR disable signal.
5. Using a voltmeter, connect the negative (-) meter lead to terminal 4 (common) of the
test board.
6. Connect the positive (+) meter lead to terminal 19 of the signal board.
A reading of 0 VDC indicates the SCRs have been disabled. A reading of 0.6 to 0.8 VDC indicates
the SCRs are active and should be gated.
With a reading of 0 VDC and proper line power applied to the adjustable frequency drive, it would
be likely that the input at power card terminal FK102 has caused the SCRs to be disabled. Given
the connection at FK102 has been verified the control card would be suspect. Check the inrush
signal as follows.
7. Connect the positive (+) meter lead to terminal 7 of the signal board.
A reading of 0 VDC indicates the inrush signal is active and the SCRs are being gated. A reading
of 5 VDC indicates the inrush signal is inactive and the SCRs are not gated.
With a reading of 5 VDC and proper line power applied to the adjustable frequency drive, it would
be likely that the control card is defective.
If the control card is suspect, replace it in accordance with the disassembly procedures in Section
7 or 8.
Should the above tests check correctly, proceed to testing the SCR gate signals.
To view the gate signals, an oscilloscope and a current probe are required.
8. Run the adjustable frequency drive while under some degree of load. At least a 30%
load may be required to consistently see gate signals produced since SCRs are only gated
when the DC bus falls below the peak of line.
9. Connect the current probe, in sequence, to each (+) positive SCR gate wire (white
leads) marked R, S, and T at power card connector MK100.
The waveform should appear as in Figure 6-16.
Figure 6.16: SCR Gate Signal
The current pulse should have a waveform as shown.
6 Test Procedures
High Power Service Manual for VLT
®
FC Series
Adjustable Frequency Drives
6-28
MG.90.L1.22 - VLT
®
is a registered Danfoss trademark
6
Summary of Contents for VLT HVAC FC 100
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