10ee blowing main fuses (30 amp)

I have a 1965 10ee modular, that has developed this blowing of the main fuses since last week when it was working like it should. I went through the normal starting procedure, letting it warm up until the green light comes on in the start push button. When I push the button, the main contactor pulls in, an in a fraction of a second, one of the 30 amp fuses blows.
I and an industrial electrician have checked what we could, but nothing we could diagnose is the problem. We have no way of checking the tubes, so am wondering if anyone can say that it is one of the tubes, or have some way to check the tubes?

Dale Nelson

So start by pulling the module.
Then check for filament to plate, grid to plate and grid to filament shorts in the C16J tubes. (they should be open circuit)
If nothing found, unhook the plate leads to both C16J tubes (prevent the leads from touching anything) and see if you are still blowing the fuse.

Bill

Yes, see if the machine runs at a single speed with the module removed, and check the module diodes, bad ones can point to the problem circuit.

yes, all the belts, gearbox and belts turn and move freely. I haven't had time to remove the module, but thanks to all who participated in this thread. I will report what I find, and if it fixes the problem

Dale Nelson

Doesn't the module have two fuses and a breaker on the back of the module board? On mine it's a 3 amp, a 5 amp, and I'm not sure what the breaker is, but if they don't blow before a 30 amp fuse on your mains, it wouldn't be in the module.

Its hard to remember every problem that has been discussed here, but I seem to remember a problem that can happen in the control "module" side of the machine, that can lead to a short in the high voltage drive end, causing the 30amp fuse to blow. Perhaps a relay not operating correctly from one of the bridge rectifiers "diodes".
I may have some more information, from the last 1983 module lathe manual and prints.

The components involved when the PC is closed.

Gearbox lock soliniod, I have had problems with these, I remove them, as only a moron would shift into back gear with the machine in motion, leave it in if there is a moron around.

Anti plugging relay

Field current timer

Resister R2

Anode Transformer T5--Supplies power to tubes anodes ET1, ET2, ET3

I cant remember having this particular problem, but often a close look at each component involved in a circuit will show something burnt.