I have a similar thread on Photrio about this but thought I'd check here. My 4550XL began flickering after a printing session recently. Then the lamp would refuse to come on, or come on and turn off again. Now it won't turn off at all.

I tried a new bulb, and cleaning the contacts of both. I also tried inserting and shifting the pins around to see if I could clean the socket contacts.

I have ensured that it's not the timer.

The socket was recently replaced, so unless I'm extremely unlucky I just don't think that's the issue. Plus the contacts were not corroded.

I called KHB and the salesman seemed very confident that the power supply is the issue. He said that he thinks the one made by Saunders for the US market has a high failure rate. I will say it is powering the fan, and it makes the familiar 'click' when you hit the focus button on my timer. Of course a new power supply is around $600 so of course I am trying to go there as a last resort.

So, just thought I'd check here to see if anyone has any suggestions for me.