RAM DBS II
Refrigeration Solid State Starter
SCR Test Procedure
DANGER! Hazard of Burn or Electrical Shock. Make certain that all incoming
sources of power have been disconnected, locked out, and tagged
prior to working on this equipment.
1. Make sure that all power sources are turned off and properly locked out.
2. Remove the motor leads.
3. Remove the cover of the bypass contactor and assure that the contacts are not welded
together. The contacts should move freely without any restriction while pushing on the
armature of the contactor.
4. Remove the six gate leads from the control board, taking note of their order. They should be
numbered from 3 to 8. If the gate lead connectors are not removed, false measurements will
result while checking the SCRs.
5. A 500 volt megger or a Simpson analog multi meter is required to properly test the SCRs. If
an analog meter is used, select the highest resistance scale (R x 10,000 scale).
6. Start by measuring from L1 to T1. Reverse the polarity of the meter leads and measure again.
The readings should be about the same. Repeat the measurements from L2 to T2 and L3 to
T3. The measurements should be no lower than 1 megohm.
7. Measure L1, L2, L3, T1, T2, and T3 individually to ground. There should be an open circuit
or an infinite reading on the meter.
8. Set the meter on its lowest scale (R x 1 ohm). Carefully measure all six gate leads. Measure
the red and white gate lead, switch the polarity of the meter leads and measure again. About
8 to 20 ohms should be measured in both directions. The readings should be within an ohm
or two of each other. Be careful not to spread apart the female plug with the meter leads when
testing. This could cause the plug to become loose, resulting in the misfiring of the SCRs
when in operation.
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Appendix C
Appendix C
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