If it's is Tungsten filament, the problem could be that the filament is crooked or not centered properly from the manufacturer side. You may want to try another filament. If it's a LaB6 filament, again the same problem. I have seen both scenarios in our Philips microscopes. Hope this helps. Good luck!

My experience extends only to Philips machines, but I guess it will be similar for other manufacturers. Before finetuning with gun settings on control desk or in software the filament has to be properly aligned in the wehnelt cylinder. So for tungsten this means after filament change: put the gun cap under a stereomicroscope and focus on the wehnelt aperture (center hole). Use the height adjustment to get the filament close to the hole but never let it touch the aperture.

Find the alignment screws and center the filament within the aperture. Now raise the filament and center it again. Repeat this procedure until the filament is flush with the aperture and perfectly in center. Remember that it must not touch the aperture. Then lower the filament 0.15-0.2 mm. Now reinstall the gun cap, close the column, evacuate and check the emission. If you don‘t get a proper emission, you cannot get a picture, no matter what software adjustments you make. I hope that helps, as I had the same process last weekend.

I agree with the previous responses. Make sure the filament is centered and set at the right height. Be sure to check after tightening as the Wehnelt can shift after tightening.

I would also recommend setting the objective aperture to its wide open position for the initial alignment. I have seen apertures severely misaligned so that no beam comes through. Perhaps that was to match a misaligned filament but now you should have a centered one. FYI, I found one JEOL aperture strip mis-adjusted so much that it was one entire hole off. There was enough latitude in the adjustment to do so. I discovered it when trying to run through the entire range of settings. I couldn't reach one end of the strip.

Finally, I know service visits can be pricey, but this could be why. Service engineers are trained to handle routine, but complicated procedures on complex instrumentation. They should also be trained (or at least have the resources) to handle the unusual situations.

I am reminded of a story (hopefully true) about Edison and Steinmetz. Steinmetz was called into fix something that Edison's engineers could not. He fixed it after only a few minutes of tinkering and gave Edison a bill for $10K. Edison protested and asked for itemization. Steinmetz obliged: 10 minutes of tinkering $100, knowing where to tinker $9900.

How true!

Thanks for all the info and suggestions! We have pre-centered tungsten filaments, but I will go through the procedure all the same to make sure that the filament is centered in the Wenhelt and resting .15-.2mm below the opening.

I'm not sure how to adjust the objective aperture, outside of the two knobs on the exterior of the machine after installation. The mechanism seems pretty fixed otherwise.

I didn't mean to imply that the technician/service wasn't worth the money. It's just unfortunately equivalent to my budget to run the lab for a year, so I have to choose between a working SEM and teaching all my classes and research activity that depends on the rest of the equipment in our cleanroom.

I would probably have to see a close-up picture of the objective aperture controls to say much more. westrasz gmail. I am used to SEMs with aperture strips where you can change the aperture size without venting the column. There should be some numbers etched onto the mechanism if you have multiple apertures. It may be that it is a budget model and has a single aperture.

I did a quick search for a JSM 3690, but found nothing. Perhaps you meant a 6390.

We are having same problem. Filament is not heating and our system model is JSM IT200.