Input Scr Test - Danfoss VLT Series Service Manual

5.2.7 Input SCR Test

The SCR can be disabled by the drive for various reasons.
Check the following before making more complicated tests.
The SCRs can be disabled as a result of an input, or lack of
input, at power card connector FK102, the external brake
temperature switch. Unless used as an input, a jumper must
be placed between terminals 104 and 106 of FK102
The SCRs are gated in sequence with the main supply. Verify
that the voltage reference signal is correct as follows.
1. Using a volt meter, measure phase to phase AC
line voltage at Terminals R, S, and T of power
card connector MK106.
2. Measurements should correspond with
measurements called out in the Input Voltage
Test (5.2.1.1).
An incorrect reading at MK106 with a correct input voltage
may indicate a problem in the soft charge card or the
connecting cable.
If the above tests reveal no abnormalities, it is further possible
that the inrush signal has not been enabled by the control
card. Using the signal test card, verify the inrush signal is present
and the SCR disable signal is at the correct voltage level as
follows.
3. Insert signal test board into interface card
connector MK104.
4. Check SCR disable signal.
5. Using a volt meter, connect negative (-) meter
lead to terminal 4 (common) of test board.
6. Connect positive (+) meter lead to terminal 19 of
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
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 positive (+) meter lead to terminal 7 of
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
drive, it would be likely that the control card is defective.
The inrush signal is also deactivated by the control card anytime
an over temperature condition exists but that should be
indicated by an Alarm 29 and a different group of troubleshooting
procedures would be in order.
If the control card is suspect, replace it in accordance with
the disassembly procedures in Section 6 or 7.
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 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 DC bus falls below peak of line.
9. Connect current probe, in turn, 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 5-12.
Figure 5-12. SCR Gate Signal
The current pulse should have a waveform as shown.
A1 > 1.1 A
A2 > 0.40 A
T1> 300 μs
Given all the other tests above were successful, a missing
gate signal indicates the power card is defective. Replace the
power card in accordance with the disassembly procedures
in Section 6 or 7.
A distorted signal may be due to a defective gate on that
particular SCR that is loading down the supply. Replace the
SCR module which corresponds to the incorrect gate signal
reading.
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