Build Your Own SLA/SLS

Hi
I've build my own machine and first I tried vivitek d910 with EC500, the results were great. But my projector broke and it was my fault. I tried to replace it with another model dh558. I couldn't even print with that projector so I replaced it with a dh913 and again I was satisfied with the results.
Can anyone tell me what should I actually look for when buying a projector? There's little difference between D910 and DH558 when I look their specs. I'm a little confused and I don't know what was the problem exactly.

i have tried viewsonic, acer, benq...vivitek 1185, vivitek 1186. My oppion vivitek 1186 have better focusing and the energy also enough to print WIC100, PIC 100, 3DM CAST,...