Sounds like it's not getting a full 18 volts.
Check for a short in the jack.
Make sure the unit is actually off when the guitar is unplugged.
If that jack tests out, check the leads on the battery box.
You will have to remove the box to check the leads.
They are notorious for fraying and breaking off.

Check out the batter box, theyre pretty flimsy. one of the contacts has broken off of mine so its time to replace the whole box.

Thanks Guys. I have just had the battery box replaced and the sustainer works perfectly again. I took it to two luthiers. The first guy did what he could and does great set-ups with the Floyd, intonation etc but he could not fix the sustainer. The 2nd Guy is probably the only person in Sydney who could repair a PC1 sustainer. Great guy as well. He replaced the battery box. The metal contacts at the bottom of the box tend to lose their springiness. He is helping me out with my other two guitars. A Jackson DK2 and a Michael Kelly MK1964.

Glad that did the trick... I still havent fixed mine yet, I need to get around to ordering the box.

If you can get to the tabs with a small flat-tipped screwdriver, see if you can bend them a bit. Might have to heat them with a soldering iron to keep them from breaking, but they should bend easily back into place.

The boxes are cheap Gotoh battery boxes... not worth the effort.
Easier to just replace it.

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