Since you did not provide the exact model number for your unit I cannot give you much precise detailed assistance. However most Hobart mixers are fitted with a standard power switch and you should not have to hold it in position for the unit to work. The switch on your unit likely just needs to be replaced with a new one.
Here is the link to the Hobart Support website and their MIXER page:
Here is a link to an example of an operating manual for a Hobart N50 Mixer:
And here is a short video of a 20 Quart Hobart mixer in operation:
And here is a short video of a 30 Quart SP30P in operation:
To view the Support Page or the Owner's Manual with Operating Instructions just use your mouse to click on the link, which is the underlined and highlighted text just above. This will open a new web browser page automatically for you and allow you to view the information at the website indicated and the contents of the Owner's Manual.
You may need ADOBE READER installed on your computer to read PDF documents.
You can download this free at WWW.ADOBE.COM
Click on the DOWNLOAD ADOBE READER button on right side of the ADOBE home page when you get there, the follow the onscreen instructions to install the software on your computer.
Please comment back here to this page if you have any details to add (like the exact model number of your mixer), have any questions, have difficulty accessing the links, or just require further general assistance and I will respond as soon as I see it.
Thank you very much and good luck.