Fluorescent Sign Ballast Mystery

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?


Reply to
Loading thread data ...

Temporarily jump the ballast from the 'good' side, to the other (take the tubes out of the good side and run temporary jumpers). That will narrow it down....


Reply to

I had not thought of that. Good idea.


Reply to









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

Reply to
[New ballast $$$]

Can you rewire to use multiple conventional ballasts?

[You'd need cold-weather rated ones....]
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that\'s close........[v].(301) 56-LINUX
 Click to see the full signature
Reply to
David Lesher

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.

Reply to

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.