The first time that I ordered from Cointaker I thought that I got a bunch of DOA's. They were all the 555 style (Push in - no twist).

Found out that the wires just weren't making contact. To this day still have some that work for a while and then stop -- usually it is because the wires are not making contact.

Every 555 that I install I pull out the wire end on each side and then pull the end toward the outside edge of the base. Usually fixes them right up.

If you have 555's that aren't working, give this a try. You might be surprised -- they are very touchy compared to old incandescent lamps.

-Chris