On Nov 14, 2:31*pm, "Chuck" wrote:
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

If the 8ft tubes have just one pin at each end, as I am pretty sure is
the case, frequently one of the two end sockets they plug in to has
two contacts that are shorted together when the pin from the bulb is
in the socket. So, when checking continuity, look out for split
sockets. I think the idea of interchanging the output from the two
ballasts is a great idea. Just watch out, the voltage, if the 5 tubes
are in series, can be the better part of 1000 volts.

Bob Hofmann