nuarc FT18V keeps blowing fuse

Hi all - new to the forum. I searched around and couldn't find anything relating to this, but I just received a Nuarc FT18V exposure unit. Nice little unit. When I plug it in the vacuum works great, but when I go to turn on the lamp, the unit buzzes loudly and lights for about 1 sec then blows the main 20A fuse. I even tried removing the bulb to see if perhaps there was something faulty with the bulb. Same behavior (only no light). When I flipped the expose switch with the bulb removed, 1sec buzz and then a blown fuse. I removed the front cover and all of the wires seem to be fine (no melts or obvious frayed/exposed wire). Everything seems clean.


Does anyone have any experience with these older units or have any idea what might be going on? The only other strange behavior I noticed is that the exhaust fan never turned on. Is the fan thermally switched to only go on when the unit heats up?

I would appreciate any feedback since I know nothing about this unit.

Thanks all!

Sounds like you have a bad ballast. My guess is that there is a short in it somewhere, which is why it trips the breaker even without a lamp.

After much troubleshooting, I nailed down the culprits (yes plural). I'll post the results in case someone else has the same problem later. First, thanks for the suggestion E76. It led me to dig deeper into the electronics to uncover one of the culprits. Also, huge cudos to the folks at NuArc who were extremely helpful and didn't charge me a dime for the advice and a scanned PDF of the manual! Now that is real customer service.

Problem 1 - thanks to the folks at NuArc, they let me know that yes, the fuses really do have to be slo-blo or time delay fuses. I was using good old off-the-shelf RadioSh fuses (yes 250v, 20A but they were not slow blow). Found an online retailer of slo-blo fuses with the right specs and switched them out. After testing with the new fuse, it still blew (bummer).

Problem 2 - Pay attention to the location of the wires on the transformer block! If you are running this on household 125, you must change the wiring from the factory pre-set 110v to the 120v setting.

Once I changed the jumper/wiring to 120 and put in a new slo-blo, voila! there was beautiful UV light. I did test the wiring on the 120v setting with the normal (quick RadioSh) fuse and it did blow the fuse. So, both steps were necessary. It seems that when it is warming up it pulls slightly more than 20A for a bit (thus the need for slo-blo) and if it is wired in 110v instead of 120, it pulls more current as well.

Hopefully this helps someone in the future! Now off to make some cyanotypes and van dyke prints!!!