[SOLVED] MC2100 Motor Controller noise from low voltage transformer

Thread Starter

hozone

Joined Dec 26, 2012
16
Hi all,
I've a ProForm 730ZLT Treadmill. Yesterday it stops working, so I restart it unplugging the main power, it works for 1 minutes, then stops working.
The motor doesn't spin, but the controller works, incline also works. The led on the board, which is a MC2100ELS-18W was on, but it didn't blink even if the controller is set to run mode.
I've removed the board, and noticed one cap is swollen, so i replace it. It was one of the two capacitor for the 9V of the control.
This morning I've used the treadmill for 30 minutes. Now it seems solved.

But there is a noise that I think is coming out from the yellow transformer, the one that output 9V to the cap that I've replaced.
The noise is little, like the hum you can hear from old radio transformer, but there is some.

Leaving the treadmill in stand by => noise
Leaving the treadmill with key inserted, display with backlight OFF => noise
Leaving the treadmill with key inserted, display with backlight ON => no noise, or so little that is almost not audible
Leaving the treadmill in stand by, with the controller unconnected => lower noise, not like if backlight is ON, but lower than the stand by mode
Un connecting the motor, or the other sensors does not change the noise.

I've checked the voltage to controller, it's 8.8V if backlight is ON, OFF< or treadmill in stand by. Nothing changed.

I think it's from that yellow transformer.
Any suggestion? Is it the usual way it has to work?

Thanks!
 

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MaxHeadRoom

Joined Jul 18, 2013
28,779
You appear to have the type of LV supply that uses a simple form of SMPS, so it operates at a freq well above the normal 50/60hz.
Could simply be loose laminations, normally you do not hear it.
 

Thread Starter

hozone

Joined Dec 26, 2012
16

Thread Starter

hozone

Joined Dec 26, 2012
16
Issue is solved. Thermal imaging helps me.
Let's take as reference the rev. eng. schematics (attached the page of interest).
I've replaced the C22 cap in the snubber rcd circuit of the low voltage regulator. I've tested the original one, it has no issue, but for some reason it resonate and produce the noise.
My new ceramic 103 1kV resistor does the job, and does not make any noise... at least for not.
However, the R9 (15K 2W) resistor (which I've tested and it's ok), gets hot.
- 45 degree in standby (after 5 min)
- 75 degree in usage with LCD display on
Have you ever check this resistor temperature? Maybe it's right to reach 75 degree?
I can put a cement 15k 5W resistor instead of this one, but I would like to understand it it's correct or not this temperature.
Also find other thermal images that may be interesting (taken after 30 min usage).

Thanks!
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
28,779
It is normal for R9 to get quit hot.
They can also be source of failure. I have added a metal HS to them in some cases.
That may not be the same one (R9) I am referring to, you may have a different board.

PS, that is not the same one I referred to.
I don't recall ever seeing one with that type of LV circuit!
 
Last edited:

Thread Starter

hozone

Joined Dec 26, 2012
16
I've not rev eng the board but is seems mine is like the one I've found in the schematic in this forum. At least in the LV part.
Anyway, I'll got for the 5W ceramic. I'll buy it and post here the mod.
I'll ley you know.
Thank you for your help!
 
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