MC2100 treadmill board full speed on all settings.

Thread Starter

TAZ023

Joined Jan 11, 2021
8
I have a mc2100 on a treadmill that stopped working.

-Initially it was not working at all I found R17 burnt so I replaced it and Q1

-Next the motor would come on very fast then shut down immediately I found U2 to be bad and replaced it.

-Next the motor comes on full speed on all speed settings and continues to run with motor sparking its running so fast. I removed the mosfet and found it to be shorted so I replaced it and tried it again only for it to go full speed again and the mosfet was shorted again. You can still switch the motor on and off even with the mosfet shorted it just goes full speed everytime.

I also tried a bench test with motor disconected and I see 108VDC when any pwm signal is supplied.

I am now looking at U5 and D13 could one of these be causing the mosfet to constantly be shorted and cause the motor to either be off or full speed?
 

MaxHeadRoom

Joined Jul 18, 2013
23,141
There is a remote possibility it could be U8 (U5) which is the mosfet driver on the reverse engineered schematic, D13 bad would short out the mosfet as it is across the motor.
Check to see if there is HV at the M+ before any command is issued.
Max.
 

Thread Starter

TAZ023

Joined Jan 11, 2021
8
I will check again later today to see if it changed but before the last test I had no HVDC on the output side of Q1 unless I was providing a pwm signal.

I noticed with a oscilloscope the folowing-
Micro pin 13- 5v pwm signal
Micro pin 2- flat voltage signal
Micro pin 8- not really seeing a noticeable signal

Is it possible to damage the mosfet without
The motor connected?

The last time I tested i had a loose lead connected to pin 2 of HD8 i was using for oscilloscope measurements that touched the heat sink and sparked and took out the LV DC so now I have to fix that as well.(I'm guessing its the 5v reg.)
 

Thread Starter

TAZ023

Joined Jan 11, 2021
8
Just took it apart and it looks like Q5 arc to the metal of the heatsink on the bottom of the board, when the LVDC gnd touched the heatsink would this of caused the arc there?
 

Thread Starter

TAZ023

Joined Jan 11, 2021
8
With U5 removed i got the LVDC back for both the 15v and the 5v.

I do not see an output on micro pin 8 still, should I see an output here when I send a pwm signal with u5 removed?
 

Thread Starter

TAZ023

Joined Jan 11, 2021
8
I'm not seeing anything unless I dont have the scope set right.

Checking u5 the output pins and -/+pins were all shorted together. Both input pins were fine and did not show being shorted.

Do you think the output on the microcontroller is dead?

Is it even possible to get a replacement?
 

Thread Starter

TAZ023

Joined Jan 11, 2021
8
So I replaced u5 and the third mosfet now.

When testing it the motor spun up to full speed again blue sparks comming out of it again once it hit full speed there was a spark from what looked like the board and the mosfet has all pins shorted again. It stops it self and if you press start again it repeats the process.

The u5 does not appear to be damaged this time but I'm starting to run out of ideas for what could be causing the mosfet to have all 3 pins shorted together(I only have 2 left).

Is the motor bad and pulling to much current(i thought i ruled this out when i tested it with the motor disconnected and it still shorted the mosfet), any ideas of what to try next or what could be causing this?
 

MaxHeadRoom

Joined Jul 18, 2013
23,141
If the Mosfet shorts with the motor disconnected and after a command is given, test the Diode on the heat-sink, it is across the motor.
Ensure the H.S. insulator is good.
Max.
 
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