Repair notes


These are repair notes. Only Steve or very senior personnel should attempt any of the repairs described here.

Orienting the IR/visible light dichroic:

In talking with one of the technicians here, this is what I've got for you. He recommends tha tyou start by adjusting the dichroic so you have an even 1.5mm gap along both of the sides that you have shown me in your photographs. You'll need a good measuring device (caliper) to do this, but start with that.

Next you'll need a good sample for field illumination evaluation. Either a solid color slide from Chroma, or possibly some diluted flourescine on a slide. Then, remove the dichroic cube from the PMT housing and install the epi turret. Look at the image uniformity only for channel 1 and remove the epi turret and make small adjustments to the dichroic position to get a uniform field of illumination on channel 1.

Secure the epi turret.

Replace the PMT dichroic and look at the field uniformity for channel 2. To correct for the field uniformity on channel two, remove the PMT dichroic (not the Epi turret) and adjust the light going to PMT 2 by adjusting the corner screws on the plate that the PMT dichroic is mounted on. This will adjust the angle of the light hitting PMT 2.

Hope this helps.

Properly orienting the PMTs (seems to be needed every 5 years or so):


When we looked closer at the photo you had sent we now know what the problem is. The PMT tube housing for channel 2 has rotated and most of the detector surface area is being physically blocked. We want the view to the PMT detector to be completely open and the PMT detector to be centered in the "window".

What you want to do is first re-align the primary dichroic in the epi turret for the correct channel 1 image as I outlined i a previous message. Then, you're going to need to physically remove the channel 2 PMT from the PMT block. Be sure you turn off the power on the PMT HV box before you do this. The PMT is secured using 4 small screws (4/40) size I think. After you remove the PMT, look near the base of the housing and see if there is a "set" screw. If there is a set screw, loosen it. [There is a set screw, needs a small hex wrench.]

After you loosen the set screw, you need to insert two 4/40 screws into two of the tapped holes in the base of the PMT. There are four tapped holes, pick two that are 180 degrees apart. You can use the same screws that you removed to take the PMT housing off of the PMT block. However, you might bend them so if you can locate two other 4/40 screws that are the same length (maybe you have an on-site machine shop?), then I would get two other screws. After you have the screws inserted in the PMT base, rotate the PMT using these screws so that the "grid" is in the center of the window. Once you get that set, remove the two screws from the base, re-tighten the set screw and then reinstall the PMT.

The PMT tube itself is inside of a small metal enclosure that is then inserted into the PMT housing (a housing within a housing). It is possible that as you attempt to rotate the PMT, it will simply rotate within the inner housing and nothing will look any better. If that happens, then you'll need to remove the PMT and the inner housing from the outer housing. To do this, you should be able to just gently rotate a little bit and with some minor pressure on the screws you attached to the base of the PMT, work the assembly apart. Then, first align the PMT tube on the window of the inner housing and then insert that back into the outer housing and align the openings. Then re-attach everything.

Depending upon what you've done with regards to tweaking the alignment of the PMT dichroic, you might have to adjust that to get a better channel 2 image.



Note: PMT housing anchor screws: #4/40 machine screws, 1 inch length, 0.25 inch lag, open with 3/32 hex wrench

Photo of a PMT rotated badly:

Photo of PMT in good position: