I have a double thorn invincible that only one tube is lighting up, I replaced the tube and sometimes it goes, I cannot find any starters and it dosnt seem to finger into life just turns on, it has the old magnetic ballast

Just found if I flick the switch off and on it will start but makes a loud hum and buzzing sound

SRS gear ? (4 wire inductive core ballasts, each with capacitor)

Are T8 lamps used ?

Are the capacitors ok (measure capacity) ?

SRS gear ? (4 wire inductive core ballasts, each with capacitor)

Are T8 lamps used ?

Are the capacitors ok (measure capacity) ?

Yes that sounds about right, I haven’t pulled the ballasts out yet, how do you check a capacitor? Apart from swapping it over to the other side.

It has 5 ft tubes, one is the old fat style and it has a new thinner one in side.

Ideally you would use a multimeter that have a capacitor test function. As capacitors age their capacity drops - In Rapid Start (including SRS) circuits this will show up as unreliable starting or reduced light output

The SRS circuit is intended to only start the T12 (fatty) lamps (for 5ft that's 65W), however, an SRS ballast in good condition may be able to start T8 lamps, although this is not guaanteed to always work

Ideally you would use a multimeter that have a capacitor test function. As capacitors age their capacity drops - In Rapid Start (including SRS) circuits this will show up as unreliable starting or reduced light output

The SRS circuit is intended to only start the T12 (fatty) lamps (for 5ft that's 65W), however, an SRS ballast in good condition may be able to start T8 lamps, although this is not guaanteed to always work

Yes it’s the thin tube that has trouble starting, I will check my multimeter has a capacitor testing setting, I know very little about fluorescent lights, I have never come across old instant start units, I will try and find another 5tt fat tube, I saw a lot of them at the library yesterday

The T12 tubes are hard to get, so if you want to keep this luminaire working with its current gear, stock on some lamps

Instant Start is uncommon in the 230V-world. An old Thorn luminaire would likely have either SRS (a type of Rapid Start), Switchstart (with starters), or Switchstart with electronic ignitors (vivatronic)

I will try to find some T12 tubes, I have some but not in 5ft

I rember seeing jumbo bins full of them everywhere when I was younger, we would always be flinging them around some abandoned building