I need EE geek help

[SSearchVT]

The touch pad speed control on my treadmill died. It's a $420 part for an $800 treadmill I bought 10 years ago - Not worth throwing the money into. The rest of the console (speed readout, incline, etc) works fine.

I've looked at the schematic and voltage chart, opened the case, used a multimeter to read the voltages, and found the right harness to work with. Three 22 AWG-ish leads (red, white, and black) ultimately plug into the motor control board. If I jumper the red and white the belt runs at full speed (all 12 VDC, zero resistance), jumpering the red and black does nothing.

My guess is that if I mount a poteniometer on the console I can get some more life out of this thing. Can someone help me with the specs? Dial, Panel mount, 0-12 VDC, and guessing from the lead size pretty low current.

[idratherberidin]

How about a dimmer switch?

[island boyeee]

i would start with a cheapo dimmer switch from Home Depot or the like. can always return it if it doesn't work

[xrocket21]

+1 to what has been said.

i have some smaller potentiometers, but they would be a bitch to turn.

[island boyeee]

or you could get a whole array of resistors with aligator clips haha

[SSearchVT]

I thought about the dimmer, but didn't know if 12 VDC would work in a system designed for 120 VAC. As far as the pile of resistors and alligator clips - I was thinking an old controller for slot cars...

[Currently]

Control voltage is typically not 120VAC.

Usually 5VDC (TTL) or 12VDC or 24VDC.

Using a potentiometer is a good idea. There are also slide switches and such you may want to consider.

Newark Electronics on the web is a good place to start.

[daviid]

I thought about the dimmer, but didn't know if 12 VDC would work in a system designed for 120 VAC. As far as the pile of resistors and alligator clips - I was thinking an old controller for slot cars...

cant give you a exact answer, but my interior trailer lights use a normal household switch to turn on and off. i dont see why a normal dimmer switch wouldnt work.all it does is increase resistance

[ZX-12R]

In what way is the speed control not working? Is the membrane keypad not responding when you push the button? Can you get the belt moving but then can't change speed? Can you give more details or include pictures of the circuits and wiring diagram?

Modern dimmers are triac based and only work with AC power sources. When used with a DC source, once they fire they will stay on until you remove power and won't give you any speed control.

If the existing controller is PWM (pulse width modulation) based, there is a chance that you could fry the motor controller board if you use a potentiometer to control speed. At the very least you would let the magic smoke out of the power electronics.

If you provide more information about the treadmill, I'll help you out as best as I can. Going forward with a repair without understanding what is wrong or how it works can lead to more damage.

[SSearchVT]

In what way is the speed control not working? Is the membrane keypad not responding when you push the button? Can you get the belt moving but then can't change speed? Can you give more details or include pictures of the circuits and wiring diagram?

Modern dimmers are triac based and only work with AC power sources. When used with a DC source, once they fire they will stay on until you remove power and won't give you any speed control.

If the existing controller is PWM (pulse width modulation) based, there is a chance that you could fry the motor controller board if you use a potentiometer to control speed. At the very least you would let the magic smoke out of the power electronics.

If you provide more information about the treadmill, I'll help you out as best as I can. Going forward with a repair without understanding what is wrong or how it works can lead to more damage.

The treadmill is a Nordictrak EXP1000. None of the buttons in the membrane keypad respond except the incline increase and decrease. So I can't get the belt to move. All of the readouts are fine.

The motor controller is PWM based... Voltage diagram should be attached. I disconnected the harness that runs from the PB-12i (power board) to the SCR Motor Controller at the PB end. I am reading 12 VDC between the red and white, and red and black. Jumping the red and white spins the motor at full speed. Nothing (or nothing good) happens when the red and black are jumped.

[ZX-12R]

It looks like a PWM signal is sent to what they call the Power Board which is then converted to a 0-12V signal and sent to the motor controller board. Since they claim the signal on the white wire is 0-12V, a potentiometer should work. There isn't enough info to determine a value for the pot but a good start would be to use a 10KΩ. Disconnect the white wire from the motor controller, connect pin #1 on the pot to the red wire, connect pin #2 to the terminal on the motor controller where the white wire was, and connect pin #3 to the black wire.

Here is a link to a pot that should would work well for this application: http://search.digikey.com/scripts/Dk...e=P16NP-10K-ND

[SSearchVT]

Thanks ZX-12R. I'll make sure to keep the fire extinguisher handy when I fire it up for the first time.

[richw]

The other wire and a 2nd high value resistor may be needed to "dump" the load so you get varying voltages from the pot. The 3rd wire is probably system ground .

yes I would start with 10K pot

scr drives work like light dimmers where trigger voltage increases the amount of the AC sweep it uses and thusly varies the DC motor voltage output.

[SSearchVT]

The 10k Ohm pot works. It's a little touchy below 7 mph (resistance increased), and I need to disconnect the power and reconnect it to get the motor spinning. Next step is get a pot with a built in disconnect, and lower resistance.

Thanks again for the help.