Last weekend, I started having problems with my Enterprise 64 and I realised there were problems with the 12V circuit. Thanks to previous posts on Enterprise Forever, I discovered the most common fault is with TR2 and C9. So I replaced them both and it started working again. I thought this had fixed the problem.

However, yesterday I plugged in the Enterprise and disaster happened! Smoke came from the case and TR2 was completely melted, and the wire to coil L1 had broken as well.

Thankfully the rest of the computer seems to work if I wire in an external 12V source... so it's only the 12v circuit that's blown. That is a big relief!

Anyway, I replaced TR2 and C9 again and patched the wire to coil L1, but when I tried power it up - more smoke started coming from TR2, so I unplugged it quick. I think TR2 must be short circuited somehow. Looking at the schematics and using my very limited grasp on electronics, I guess the culprits are going to be C10, TR3 or the coil L1. Does anyone know how I might narrow this down? I have a multimeter but don't have access to an oscilloscope. Is it even possible to get a replacement coil???

All help gratefully received.

Thanks for the tip, Pear. I'll get some 0.25mm enamel wire and give it a go myself.

Is there any way to confirm whether it is the coil that is causing the problem? Could it be another component that is causing the short?

Good idea about EPower, although I think I don't really want to replace everything. The 5V is working fine.

Do you need your spare coils, or would you be able to send me one? It would be great if I could fix it.

I have used different BC337s with no problem. But I can't remember if they were -40s or something else, sorry!

Thanks - that's good to know. So hopefully the transistor is good.

I'll try adding some more windings to the coil. I'm aiming for 14.5V input to the 78L12 regulator.