anyone know how to diagnose a faulty Choke / Ballast in fluorescent light circuit

Question

Hi allI'm hoping somebody knows more about this than I do.We have a standard fluorescent light that has stopped working.I have replaced the tube and starter with known working ones andstill light doesnt work.With the light switch on, I measured 240 volts going into the Choke,but zero volts coming out of the choke.From this I assumed the Choke was faulty (is this a correctassumption)Also I took out the Choke and no current passes through it using anOhmmeter/Multimeter connected across the 2 terminals.Again I figured the Choke must be faulty / open circuit from this (isthiscorrect?)I then replaced the 40W Choke with a similar thing from an old fittingcalled a Ballast hoping this would fix the light.It didnt - although for some unknown reason the light did come on for about 5 minutes then died after putting the outer light casing back onfor the night????Now when I switch on, there is a very dim light just at both ends ofthe tube.By the way the ballast I put in is 65W (is this important when the oldunitwas a 40W choke. The light tubes are 40W.)I am still left wondering if the Choke is faulty, and if it is thenwhy isntthe replacement ballast not working. (Yes I did connect it up the sameway)Thanks for any help and advice(Im surprised this isnt more of a common problem - I couldnt findanyoneexperiencing this same problem)RegardsNick

Frisket · Accepted Answer

Very likely.Same thing, different nameI think the old  choke has probably bitten the dust. Someone else isdoubtless an expert on these things but I always try to replace like forlike when swapping components - 65w is considerably more than 40w - maybethe 1st firing killed your starter.

BigWallop · Answer

Stop there. If you've replaced both the tube and starter lamp and it still ain't working, then the fitting itself is at fault and needs replaced. You don't have to go any further with more tests and the like. You need a new fitting.

impvan · Answer

Yes, the choke's knackered.You haven't come across anyone else with the problem as chokes don'toften fail like this.  They normally develop shorted turns and melt,then go bang.

Chris Oates · Answer

and stink like hell

Terry · Answer

Not sure if this would apply to your 230 volt versions but I have usually found that a faulty "ballast/transformer" (as we call our

115 volt and various other voltage versions) will have an open primary/mains input winding. However ours, unless they are very old like 40 to 50 years, do not use 'starters'. ballasts for the last 40 or so years have incorporated a thermal cut out in case the ballasts overheats and AFIK it does not reset thus protecting against shorts and potential fires. And yes, some of them do ooze black 'goo'. Which these days is said to be not of the 'cancer causing' variety. i.e. PCBs! Some appliances do use just a series choke in a very simple inductive circuit to fire the fluorescent tube/s. Idea anyway.

Chris Oates · Answer

series choke here, no thermal protectionnot suitable as raceway even though theyare used that way.

BigWallop · Answer

You better believe it.

The Natural Philosopher · Answer

No, it doesn't. We have enough strike voltage without needing a step-up transformer. but I have

Dave Plowman · Answer

Hmm. It might be one of several, and or no longer available. What's wrongwith fixing it? I've put electronic ballasts in old fittings before now to retain theappearance.

nick · Answer

Thanks for the adviceSeems that it is the choke then (still not sure why the replacement 65W ballast didnt work though - unless thats bustedaswell)I will find out how much a replacement choke costs before probably buyinga complete new fitting.Much Obliged Nick

Dave Plowman · Answer

A 40w choke costs 3.85 + vat from TLC.

anyone know how to diagnose a faulty Choke / Ballast in fluorescent light circuit

Join the Discussion

Didn't find your answer?