Bosch ROS not powering on

If you've replaced the variable speed unit in your Bosch 11318EVS SDS-max Demolition Hammer and the variable speed is still not working, there could be a few potential reasons for this issue. Here are some steps you can take to troubleshoot and address the problem:

1. Check Wiring Connections: Ensure that all wiring connections related to the variable speed control are properly connected and secure. Loose or damaged wires can disrupt the variable speed function.
2. Control Switch: The control switch itself could be faulty. Test the switch to make sure it's functioning as intended. Use a multimeter to check for continuity across the switch terminals in different speed settings.
3. Speed Control Potentiometer: The potentiometer, which is responsible for adjusting the variable speed, could be malfunctioning. Test the potentiometer with a multimeter to ensure it's changing resistance smoothly as you adjust the speed.
4. Electronic Control Board: The issue could be with the electronic control board that governs the variable speed function. Inspect the board for any signs of damage, such as burnt components or solder joints.
5. Brushes and Carbon Motor Contacts: Worn brushes or carbon motor contacts can affect the motor's performance and, consequently, the variable speed control. Check the condition of the brushes and motor contacts and replace them if necessary.
6. Power Supply and Voltage: Ensure that the tool is receiving the correct power supply and voltage. Incorrect power supply can affect the tool's overall performance.
7. Manufacturer's Support: If you've exhausted your troubleshooting efforts and the variable speed is still not working, it's advisable to contact Bosch customer support or a professional tool technician. They can provide more specific guidance based on the model and diagnose the issue accurately.
8. Professional Repair: If the issue is complex or involves internal components, it might be best to seek the assistance of a professional tool repair technician who has experience with Bosch power tools.

Remember that working with power tools and electrical components carries inherent risks. If you're not comfortable or experienced with tool repairs, it's recommended to seek professional assistance to ensure safety and prevent further damage to the tool.

Question edited for clarity.
Question moved to correct category.

Not many spares are listed

https://www.google.com/search?q=WEN+7%22+2+SPEED+SANDER+MODEL+943+parts

Try the maker direct.

Parts - WEN Products

https://wenproducts.com > collections > parts
8.5-inch Sanding Pad for WEN 6369 Part Number: 6369-003 Compatible with the following Model: WEN 6369 Variable Speed 5-Amp Drywall Sander .

Check for worn out brushes and damaged armature.

Sounds as though you are on the right track. I would take it apart, and see if the trigger could have some dirt or other material causing it to stick, or is it worn to the point that it needs to be replaced. Good luck!

CHECK TO SEE IF THE BOLT HOLDING THE DISC TO SANDER IS NOT LOOSE.

check the board with the variable speed control knob, mine failed once and would not power on. I believe I started having the same problem for the second time today.

The 3725 had an overlap winding problem in the armature allowing no full power under load, I replaced mine three times before getting a good one, best 5" on the market tho.

It is either a bearing or bearings that are failing and causing the sander to slow down or the variable speed switch is failing.

if this is disk type grinder make sure you did not knock the disk out of alignment when it fell off table if so remove and re-align or replace disk seen it before make sure

When you are finishing the surface of wood, it's vital to maintain control. Work too fast or too slow and you risk ruining your hard work with unsightly scratches