Problem with light fitting

[Chippychap]

Hi Guys, I have this light fitting

http://www.ikea.com/gb/en/catalog/products/30135700/

It's been up about five years, fitted just before we bought the house.

Blows bulbs like nothing else, and one by one the new bulbs didn't work, now only the end lamp works when bulbs replaced.

http://www.ikea.com/assembly_instructions/beryll-quad-spotlight__DFP301_PUB.PDF

I can take it down but what could be wrong with it or should I look at replacing the whole unit?
Thank you.

 

[sparkwright]

A loose connection, bad contacts to lamps, or plain cheap lamps are possible answers.

 

[Chippychap]

Thank you for that.
Would there be a loose connection for each of the lamp holders or could one affect them one by one until only one will work with a new bulb?
I have also tried tightening the two clamps that hold the bulb in.
I'll have a shuftie when it comes off.
Thank you again.