Melitta LOOK - Maintenance; Functional Checks; Problem Analysis; Test Equipment Required for Fault Finding

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Section 5. MAINTENANCE
Periodic maintenance is not necessary. However, periodic inspection and test is
recommended.
5.1 Visual inspection
Isolate all supplies and withdraw the module from the case using the two black
handles on the relay. Inspect the printed circuit board for any sign of loose
components or connections.
Note that, where fitted, flag mechanisms should not be disturbed unless found to be
operating incorrectly during the routine function tests.
Your attention is drawn to the fact that the relay can be damaged by electrostatic
discharges. The pcb should not be touched unless precautions have been taken.
5.2 Functional checks
Periodic function tests should be carried out using the test procedures shown in the
commissioning section.
The operation of the trip indicator and the reset facility should be checked during
these functional tests.
Section 6. PROBLEM ANALYSIS
These instructions enable a fault to be localised to sub-assembly level. Fault finding to
component level is not recommended. The main reasons for this are as follows:
– Fault finding on printed circuit boards requires the use of specialised knowledge
and equipment.
– Components used in manufacture are subject to strict quality control and in
certain cases selected for particular characteristics. Complementary metal oxide
silicon (CMOS) components are used, which require extremely careful handling.
– Damage can be caused to the printed circuit track unless extreme care is used in
the replacement of components.
– Replacement of some components will necessitate recalibration of the relay.
– The printed circuit boards are covered with a protective coating of polycoat
which makes access to tracks and components very difficult.
6.1 Test equipment required for fault finding
Equipment required for fault finding is minimal and consists of the following:
– Digital multimeter with ranges of 0 – 1000V ac/dc and 0 – 1A ac/dc
– DC voltage supply 30V 0.5A
– AC voltage source 0 – 500V 50Hz at 10mA
– Oscilloscope (optional)
– Relay tool kit