Thanks a lot for the info Bushy260. I have taken some photo if still required.

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Based on the manual you have referred to me, i took a photo below of where i think the diaphragm is. If this is the one, how can you tell if the diaphragm does really need replacement ? Is there anything i need to look out for when i open this e.g. spring bouncing out once you've removed the screws ?

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