Welcome to ECN,mate!.
I have lots of experience with Fluorescent Lighting.
Invariably my Faults work, means I fix heaps of Under-verandah fittings hooked up to the Street-Lighting circuit, in town here.
So are we talking a Twin tube fitting?
Usually a Ballast will have a reasonably low resistance, our 230V ones over here, have a resistance of 57 ohms when new.
What is the fitting doing?, no light from one tube?, Tube flashing?.
Check the starter and the lampholder contacts first.
Then discount the ballast.
Let's face it, these days if you're not young, you're old - Red Green