FB3 colour channels, some help please?

[norty303]

If you own an FB3, could you measure the colour channels of it with it powered but idle please?
I'm seeing some mV on mine which are causing my new 445 to be on all the time (albeit very dimly) and wondered if this is common across all of them?

A multimeter will show some signal just fine but if you have a scope, even better. I'm having emails with Bill about this but this will help determine what is 'normal' or not. I think it may just be down to the very low threshold to switch the 445's completely off, however I'm seeing it worse on the blue channel, so its exacerbating the problem.

many thanks

[norty303]

Ok, thats great, I'll just accept thats how they are then. Still a bit of a bummer in a dead blackout situation though.
How easy would it be to build in a buffer of some sort that only started passing signal above say 100-200mV?

[-bart-]

Excellent opportunity to install a shutter
My aom has a finit extinction ratio, so I'm forced to use a shutter too.

[norty303]

Really, we're packed full to the rafters already, I'm not sure a shutter will go in.

[CRFultz]

I read .0221vdc on the red and green. The blue has no laser connected and it reads .0017vdc.

[norty303]

My 445 does produce weak output when it's at idle.. but it does that with 0V on the flexmod anyway

I can get my 445 to go off with the bias very low, but when i plug the FB3 in, it comes on with the very little voltage present.

[norty303]

Thats exactly the problem, the bias is virtually zero to get it to go off, so the very little V present on the FB3 is just enough to get it back on again. And as you can't go below zero V on the bias you can't possibly stop it giving output.
Maybe I just need to see it in the dark with no lights and smoke and see how it looks out of the front

[ElektroFreak]

I see.. I'm thinking that short of a shutter there probably is no solution other than to live with it.

[DZ]

How easy would it be to build in a buffer of some sort that only started passing signal above say 100-200mV?

A simple diode in series with the color channel would work. Something on the order of a 1N4148 would drop about .7V, a 1N5711 would drop around .3V or .4V.

Something else to consider, and a big reason a shutter would help substantially, having the bias set kinda high is a good thing. On my projector, the bias for red is set high enough that if the shutter remains open when the beam is stopped, you can plainly see about a 2 or 3mW beam. I find that this significantly improves linear response. In fact, this, in conjunction with the color board, I just about completely eliminate color tails, even in images as they fade to black.