I have a customer with a portable flashing arrow sign that is permanetly mounted. The fluorescent bulbs were not working. I found a wire shorted on the frame. Repaired it and replaced the ballast (T12HO). It was working fine when I left. A few days later they called and now the fluorescent lamps will light for 1 second when the sign is turned on and then go out. I can turn it off and back on and it lights 1 second and then goes out again. Ballast?? I just put a new ballast in it.
Did you check the flasher module yet? It may have crapped out. Maybe try bypassing it just to see if the lamps stay on continuously. I would also check the lamps themselves, wiring and sockets again as well. I can't remember the last time I saw a flashing sign that used T12HO fluorescent lamps with a ballast though, mostly neon with a transformer, incandescent or LED.
The flashing incandescent lights work fine. It is the fluorescent lights behind the sign that come on for 1 second and then go off. Yes it is an old sign.
T5HO and T8HO ... But T12HO?
(I'm in California -- and T12s have been banned hereabouts for years and years.)
My first impulse is to say that the ballast is a mismatch. (I'd junk the T12s and move to T8s.)
BTW, shorting neutral conductors on the frame is a classic cheat for systems that have too much impedence on the neutral.
I'm forced to presume that said short was accidental. If it was a hot -- I'd wonder about the C/B and the grounding/bonding conductor.
Lastly, always swap out the tubes for a known sweet set before tearing your hair out.
A system with a 'casual' short may also have issues in its tombstones. (This issue is much, much, stronger with exterior signage. The conductors are dinky and the contact surfaces are minute. They may permit a start surge to pass -- and then fail to sustain normal operation.)
8' T12HO lamps for replacement use are still available in CA. at both Home Depot and Lowes.
http://www.lowes.com/pd_327859-3-28984_0__ Ballasts for them may be a different story altogether.
Sign ballasts should be avail. just expensive.
I was back out on this job again yesterday and the lights were working again. I customer states that if the temperature is above 30 degrees, it works fine. Below 30 degrees, it won't work. Does this make sense?
Do you have HO lamps that are rated 'CT'?? Not all HO lamps (8') are cold temp. Check the bulbsfor something like 'F96-T12-HO-CT' with a color temp somewhere in the mix.
Could be that the bulbs are not seated in the tombstones or sockets.
HO signs I have worked on in the past, have sockets mountedin punched holes in a sheetmetal channel on each side. Signs that are 'aged' may have weak springs in the sockets, or the frame that the sockets are mounted in may be slightly expanding causing bad contact at the sockets.
Did you notice any slight signs of arcing at the bulb ends, or on the socket contacts?