"Chuck" wrote in message
news:OelTk.434677$yE1.398334@attbi_s21...
cut and pasted from alt.engineering.electrical

I am helping a friend who owns a restaurant fix the marquee sign in his
front parking lot. The sign was working fine for the last 3 years. The
sign uses two separate banks of 5 linear 72" (F72T12/D/HO) tubes per
ballast. The pin style is recessed the bi-pin. I think the voltage is
220VAC. Unfortunately, the label on the ballast has aged away and is now
unreadable, but I am quite sure it is one of those pricey six tube
ballasts
rated at up to 36 feet. There are a total of two ballasts, one for each
bank of five tubes, for a total of ten tubes. One bank of five tubes
works
just fine. However, on the other set of five, only the tube, the one
physically closest to the ballast lights up. All of the bulbs have been
confirmed to work by removing them and testing them in the working lower
socket. I think this is just an open wiring problem. I now need to
troubleshoot this bank of tubes while standing on top of a 12ft step
ladder
in the middle of a parking lot.

Due to the cost of a new sign ballast, I want to do everything else
possible before ordering a new one.

Troubleshooting Questions:
- Since one lamp still works, can the ballast itself be considered 100%
good?
- Could one open wire in the mix cause these 4 other lamps to fail to
illuminate?
- Is there a dependency where all 5 bulbs need to be in-place and working
for all 5 to work?
- Should I use an inductive hi-voltage tester to sense the voltage to the
sockets?

Chuck
I replaced the single known-bad bulb in the unlit bank of four and..... they
all lit up. The single lamp on the bottom that was always lit was wired to
another ballast (I overlooked) from the lamp bank on the other side. In
conclusion, there were a total of three ballasts, two four lamp sign
ballasts and one two lamp sign ballast. Problem solved. Thanks for helping
me think this through.