Thank you sewbizgirl! That is exactly the info I needed!
This is the electronic version of 830, so no capacitor in the foot controller, and no fast/slow switch on the back as with the 730 or 707 (which I have worked with). The foot controller should regulate the motor to run slow, as it is controlled by an electronic circuit board, but there is no response at low foot pressure, only full speed at full foot pressure. Tomorrow I will check the brushes and clean the commutator. If that doesn't improve it, my next trick will be to find a replacement circuit board. I would rather not pay $90 for an after market foot controller that is said to be less sensitive than the original. I will report the results! Thanks for your help.