Bathroom mirror light not working

[ThomasFoster]

I wonder if anyone could help - I have a bathroom mirror light that recently stopped working. It has four flourescent light tubes in it, I have tested them with a multimeter and they all seem okay. It has an infrared sensor to turn it on and off - I thought that could be the problem and fitted a new one, but it made no difference. Is there anything else that commonly goes on mirrors like this? I expected there to be some kind of starter for the light tubes but there doesn't seem to be one. There are two boxes with 'electronic ballast' on them inside of it, whatever they are?!
I know I could just get a new mirror, but I like this one and would prefer to fix it if possible. Any advice would be appreciated!

 

[terryplumb]

Have you measured the voltages present at the mirror, at its supply cable connections ?

 

[ericmark]

The starter and magnetic ballast has been replaced with the electronic ballast, be careful as these can produce high voltages which can damage a multi-meter so better not to try measuring the output, since there are two, it seems unlikely both would fail together.

For a 8 watt fluorescent I would measure around 7 volt across the heaters and 120 volt end to end until tube fired then down to around 2 volt and 50 volt. It will vary with tube size and the way the electronic ballast is wired, the latter versions did not use heaters and used a lot higher strike voltage.

So better only to measure voltage into the electronic ballast.