Thanks Bill very helpful. I'll dig a bit and see if the thyristor ca't be replaced, that is if I can find any specs or numbers on it....
Finding the part number is the challenge if it isn't stamped on the part. This is a good time to have a bud whose hobby is electronics or just do it yourself if you feel adventurous. If it's the stud-mounted type then removing and replacing it is pretty straightforward if you can do electronic soldering (this is where the electronics buddy comes in handy). If you DIY, you need to put a dab of thermal paste/compound between the thyristor and the heat sink.
... But if I am understanding this correctly, with the thyristor a dead short, there is no inverter-like action so the DC motor is getting straight AC modified by whatever on the circuit board remains in the loop. It shouldn't run at all. But it does.
That's probably correct, but there might also be a failure mode in which the thyristor behaves as a regular diode rectifier, but I sort of doubt it.
There might be a bridge rectifier upstream of the thyristor that is converting the AC to pulsed DC.
Also, some types of DC motors are perfectly happy with AC power. Handheld power tools such as drills, routers, and sanders all have series wound universal motors which are one kind of DC motor.
The reason for the motor overheating could be because the failed thyristor is causing the motor voltage to be too high.
Bill, I was just clarifying, and not implying you were foolish. Please accept my apology if it sounded that way.
I didn't mean to imply that you were implying.
I was just tongue in cheek saying that I was foolish for thinking that the manufacturer would design the treadmill to be fail-safe (meaning fails to a safe condition rather than a dangerous condition such as the treadmill suddenly taking off at warp speed).
This machine has become almost a throw away machine, unless you are exceptionally talented in designing electronic work arounds, or can troubleshoot circuit boards. If you nurse it along with one kind of fix, you will also run into an issue with another electronic part sooner or latter. Just saying, about everything in that control box has failed for someone. At one point, there was blame put on people turning bowls and "overworking" the electronics. It's a great machine, until it fails. Then you have to decide what kind of money to spend. If you have a type 1, that was the original machine. Those machines had a ton of issues with switches. I'd vote for buying a new lathe and move on from this money pit. By the way, I have a type 2. Still hold my breath every time I use it. Don't believe me? Just Google 46-460 failures.
Switch problems seem to be almost universal on imported power tools, not just this particular lathe. When it comes to Googling for gripes, we all know that the Internet is the place to go for rational well considered product reviews.
Delta went through a tough transition when they were spun off by Stanley tools and the big problem at the time was they were suddenly without a repair parts network. Quite a few other members in my club have the Delta midi lathe and I haven't heard of any problems. I have used that model on numerous occasions in classes and have always been impressed. I think that John concluded it was operator error that was the root cause of the current problem so beating up on Delta seems a bit out of context.When it comes to the hyperinflated price of repair parts, unfortunately that's standard practice for everything.
I checked the Grainger catalog to see what the prices were for DC motor controllers and they were even higher than the Delta price.