Rockwell Automation 1336-SN-SP20A Snubber Board Kit - Manual (Page 24)

1336-5.40 – August, 1999
I-24
9. SCR checks:
10. The Diode and SCR checks in steps 7, 8, and 9 above show a
range of acceptable values. These values will vary depending on
the type of meter used, analog or digital. Most analog meters do
not have a diode scale, while most digital meters do. In general a
Diode should never be shorted from Cathode (1) to Anode (2). An
SCR should never be shorted from Cathode (4) to Anode (3). An
SCR should read a relatively low resistance from the Cathode (C
or 4) to the Gate (G). An SCR should never read open resistance
from the Cathode (C or 4) to the Gate (G).
SCR and Diode Assembly
Replacement 1. If a Diode or SCR require replacement, the entire upper or lower
heat sink assembly must be removed from the IGBT and Pre-
charge assembly steel frame. Remove the heat sink guard com-
pletely. Remove the square shaped bus bar on the left side of the
IGBT and Precharge assembly, refer to Figure I-12. Remove the
screws that attach the precharge back-up plate to the steel frame,
four screws for the Diode heat sink, two screws for the SCR heat
sink (Figure I-13).
2. Once step 1 is complete, the screws that hold the heat sink to the
precharge back-up plate should be loosened one or two turns, but
not removed. The heat sink clamp nuts can be removed. Note the
polarity of the Diode or SCR and remove the defective
component.
3. Apply two drops of silicone oil to each side or face of the new
Diode or SCR. Clean any dirt off of the original heat sink
mounting surfaces. Install the new Diode or SCR, with the same
polarity as the original component, in the heat sink (refer to
Figure I-13). Tighten the clamp nuts to 28 N-m (240 in.-lb), while
holding the heat sinks flat against the precharge back-up plate.
Tighten the precharge back-up plate to heat sink screws to 9 N-m
(75 in.-lb).
Meter Leads
Ohms Reading Diode Scale Volts
3 4
+ - 1 to 3 M
Ω
Open
- + 1 to 3 M
Ω
Open
C/4 G
+ - 5 to 20
Ω
0.005
- + 5 to 20
Ω
0.005