I have a infocus IN35 that at 100 hours burnt out a bulb. Thinking that it was just a bulb problem I bought a new bulb and it lasted 20 minutes. a t.v.repair shop said its probably the ballast that is the culprit but they could not supply one to fix it. my question is. Is this a common problem and where do I get the part?

I seemed to have had the exact same problem... I had placed the projector on top of a small book (to raise the unit), however, did not rest the feet of the projection unit on the book and it overheated and turned off, as a result. (The bottom of the unit was making direct contact with the book which caused it to overheat since not any air was passing through between the two)

After letting it cool for a while and powering it up -- it would usually power off completely for about 15 minutes. After a little thinking, I thought it may be the lamp/bulb and waited a couple of years and bought one online that arrived yesterday.

I installed the new lamp/bulb this morning and it did the same thing. It powered down about a half hour later. Bummer.

I reset the machine to factory defaults and checked to see if it had the 1.03 firmware... It did

Then went through the settings in the setup area and turned off the 'prevent pic screen saver'... Reset the 'lamp hours'

I doubled checked the lamp/bulb installation... Turned it back on -- same thing -- it shut off after about 15 minutes or so... Then unplugged the unit and turned it over and took out the 4 or 5 chassis screws and loosened and took off the side panels and blew onto the fans and circuit board areas and gently pounded the sides to shake anything that shouldn't be there loose and put it back together.

i powered it back on and now it's been working for about 2 hours and 16 minutes!

good luck!

I had the same problem so removed the bulb which is very easy, only 3 screws, found the wire mesh inside was covered in dust so vacuumed using a brush head attachment, removed all the dust & did the same to all the external vents too. The projector now runs smoother, quieter & does not over heat after hours of continual play. Hope this helps, Chris

This is a clear indication of a new bulb requirement

Sounds like the power supply is weak if it has to run for awhile before it functions. The control board could also be the issue. Does it make any grinding or buzzing noises?

if the new lamp doesn't have a problem, then it's not the ballast, it's just a bad bulb. especially if you didn't get it from infocus. the cheaper lamps don't last long. you get what you pay for.

Exchange the lamp under warranty...
You've tried almost everything else.
It's not that uncommon to experience "infancy failure" with a brand new lamp.

If the problem persists with the replacements replacement then I would suspect the Lamp power supply (Ballast) is failing.

I experienced the same thing, only to discover it was the ballast that powers the lamp. I believe INFOCUS repairs for $390.00 per the technician that I spoke with on the phone at INFOCUS.

we were unable to pull the projector menu & it also took about 2 hours for the bulb to turn on.......the fan works, have changed the bulb, closed the bulb door & tried to reset the projector.......help!

I can almost guarantee that your bulb is out. We probably have 20-30 projectors of this model in the school and bulb life averages a little over 100 hours even though they advertise 3000 hours. Infocus has been known most for their poor cooling system to the bulb over the years and most owners won't get the life expectancy of the bulb. If you remove the bulb you will find a small restrictive vent screen on the bulb and commonly it will be filled with collected dust. This model really doesn't have any removable/cleanable filtering system installed - again a cheap and poorer design then many other brands. We have decided not to purchase infocus projectors anymore in the district. They were a seller at one time because they were cheap, but because they don't last they weren't really a deal after all. Sometimes though a ballast for a projector will go out and it will be unable to power up a good bulb. I wouldn't consider fixing it because of their overall poorer reliability.  If your looking for a cheap but more reliable brand of projectors I'd steer towards Epson projectors. They tend to have lower costing projectors and bulbs then most and I have seen in person that they last well above their advertised lamp hours in different models. Their are many good brands out there but InFocus is not really one of them - they have under built projectors and poor phone support. 
Hope this helps a little. - Scott

get it from projectordoctor.com or from infocus. do not get cheap replacements. you get what you pay for.