So, help me out here, this has to be the strangest fault I’ve ever had on a ballast! Put this gear on a tray this afternoon and hooked it up to a lamp, it didn’t work! Thinking it was the ignitor I changed it for another one, still didn’t work?, a third ignitor also didn’t work! Dug out the multimeter and was getting mains in at point 1 on the photo, and a rather odd reading of 149 volts at point 3?, the same voltage was present at B on the ignitor, but no ignition voltage? Thinking it was a ballast problem, I decided to take it off to do a resistance test, here’s where it gets weird! Testing between points 1 and 3 I got nothing!, no continuity!, but testing between points 2 and 3 it was perfect! I then tested between points 1 and 2 and again got nothing!, it was then I noticed the block on the incoming was an odd shape, bulkier than the out going block!, do these VS ballasts have a tiny inline fuse here?, as when I spun the block around on the incoming, the ballast lights the lamp perfectly! I can honestly say I’ve never come across this on any ballast before!

They have a tiny fuse and it's crap. Moisture kills them (they corrode) just replace with a standard bit of terminal strip. Problem solved

That explains everything, but I just rotated the block around so I have straight through connection to the incoming , how many ballasts have this on then?, and why did I get a voltage present at point 3 the first time I measured it, but no continuity here when the ballasts wasn’t energised?

I’m presuming this is the fault I came across a few times on Alpha 4 90w ballasts! I had the same with those but presumed they were oc !

I’m glad Rich confirmed my suspicions!, this proper fried my head!

Interesting, that explains the strange looking terminal block on some VS gear then! Is is a thermal fuse or just a normal fuse for overcurrent? I assume it is there to protect against rectifying lamps?

But what a stupid idea from VS? So if you didn’t know about it, you’d bin the whole fitting or change a ‘still working’ ballast!?

They're crap. Had some pretty much new Thorn Sonpak fittings that had stopped working. This was the fault. Changed the ballasts before closer inspection revealed what the issue was. There was a tiny bit of condensation in the fitting and this stupid fuse / thermal link had corroded. Fuck all wrong with the ballast that a standard bit of terminal strip didn't fix. Just annoying I only worked it out after changing them

Yes that is crap, guess that is what they wanted people to measure the ballast and assume it is dead so buy another. Handy to know now if I ever come across any though!

I had something similar at the national grid yard with tridonic ballasts - they looked mint no output at all. Behind the ballast plastic was a thermal fuse which is displacement connectors and the connections had failed! Replaced with a bit of 1.5 T&E core

It says it on the laybel, with thermal protection. And because VS seems to have imported their engineers to Germany they decided to put the thermal fuse in the terminal, instead of onto the coil directly. Another problem with these is the secon screw of the Terminal, the one that connects to the ballast. VS welds a metal tap on the ballast bevor imprgnation. They then rely on the screw damaging the warnish for the connection. Obwiously its useless and I had a termional burn away that tap an a 700W MB choke by them. Since then I avoid them. I prefer Philips or good old Magnetek/May and Christe chokes...

At least it was repairable with a bit of cheating