Finish Thompson BE-15/15C - Manual (Page 23)

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 If the LED goes out, then the probe itself is making contact to ground. This can be confirmed by
checking continuity between the terminal on the top of the probe and the pipe.
If there is continuity, remove the probe from the pipe, and thoroughly clean the probe and the inside
of the pipe. Residue build-up can form a “bridge” between the probe and the pipe. Check whether
the probe is straight. If the probe is slightly bent, it may touch the side of the pipe. Straighten if
necessary, reinstall the probe and recheck for continuity.
Possible Cause 3: Level Control Board failure.
Disconnect electrical power to the BE unit before performing tests
on the Level Control Board.
Check the contacts
on the Level Control Board.
Check for continuity between the “NO” and “COM” terminals on the lower right corner of the Level Control
Board. There should not be contact between them when there is no liquid in the Process Tank or no power to
the unit.
If there is continuity, the Level Control Board is defective and must be replaced. If this has occurred, check
all electrical wiring for shorts. See the “Important” note in the beginning of the “Service Procedures” section.
CAUTION: