Hi Andrew,
I've rebuilt/fixed many treadmills and I've found the following.
On our (USA)120V mains a 90V motor is used with an SCR bridge controller.
A PWM controller running off of about 135VDC is used with a 130V motor.
Double the voltages an you get what you have.
It's possible somebody may have mated the wrong controller to your motor.
If this is the case then it could be what caused your controller failure. I can post
a
SCR type controller in the dropbox if you want it. It's output is a form of PWM
on full wave rectified DC. Go here http://en.wikipedia.org/wiki/Thyristor and scan
down about 1/2 way to "Applications" and see the graphic.
Art

wrote ...
Hi Folks,
I know a lot of you are across a few more subjects than metalworking,
so..

Looking for a practical "I can build it" speed control for a 180V DC
treadmill motor I got. The original controller is stuffed, traced the
fault to (surprise) the MOSFET driver cunningly encapsulated in epoxy,
so no hope of seeing what it is. Plan to keep the DC supply (which is
375V DC after full wave rectification from our 240V AC mains supply.)
and the existing MOSFET, back EMF diode, and what LOOKS like a zener
on the gate of the MOSFET (drive limiting?)

I have a vague knowledge of how the things work, but not at the
voltages this will use - how do I limit input motor volts to 180v ?

Ideally, would like dynamic braking, constant speed (there is an
optocoupler on the back for a feedback circuit) forward/reverse etc
etc...But would settle for a plain vanilla stop-slow-fast-flat out
controller.

Anyone got a circuit I could copy? - its no use sending me links to US
suppliers, the logistics of getting it here are hopeless.

Besides, I wanna build it meslef (and that should resonate with you
guys)

Regards,

Andrew VK3BFA.