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Can anyone help me find a PCB fault? Answered

Hey folks, I'm hoping someone can help regarding a fault on my motor controller board for my treadmill (Tunturi T85).

The error message is (system check failure), which according to the manual means it's related to the motor control board.

When I turn on the treadmill at the main switch, the motor powers up for a split second, it does 1 rotation and then stops. I'm pretty sure that shouldn't happen as it would be a safety issue.

Also when powered up I hear a relay click, I hear the same click when powered down.

The board switches 240v ac to 130v dc for the main motor, there is also a smaller motor for the incline.

I don't know much about this stuff, but from looking at the capacitors they seem good. One felt to have a bulge in it, so I removed it to test and it's fine. I also changed a resistor that had a small dark spot on it.

I've scoured the internet for possible faults but there's little info on this brand.

Any help on how I can test individual components or continuity of the circuits would be greatly appreciated :D


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10 months ago

Good news, after changing a few MOSFETs (I think a couple of them were fine, but wasn't sure) the treadmill runs.

However, while I was testing it it had another issue. The incline motor tried to self calibrate and didn't know when to stop. This cause the machine to think the motor was being overloaded.

I think there must be a problem with the incline sensor, I'm not sure what type it is I'll add a photo later.

So kind of good news, and a bit of bad :D

Jack A Lopez
Jack A Lopez

11 months ago

Well, my prejudices tell me that, if there is any particular component on this board, to be suspected of failing, it is probably one of these big silicon based slabs (probably MOSFETs if the motor is DC) switching current to the motor.

Usually these are connected to a big aluminum heat sink. I am guessing I do not see this heat sink in your picture, because you removed it for some reason.

I tried looking at the User's manual for this treadmill, model T85,

I also found a Service manual for T10 (it says applicable to T20, T30, T40 as well) what I am guessing is an earlier version of this treadmill, here:

The User's manual suggested contacting, "the dealer" in the event of a persistent error code. Quote:

"If the display shows an error code (marked with “E” + number), restart
the equipment and check whether the display still shows the error code.
If the display still shows the error code, immediately contact the

But the success of that approach will depend on the character of the dealer. You might ask dealer if he or she can get you a copy of the Service manual, or a circuit diagram for the motor controller board.

The T10 Service manual had a suggestion for something fun to try: a secret service menu: Engineering Mode!

Engineering Mode
1. Enter the engineering mode after switching the treadmill POWER ON by pushing first ‘SELECT’ and then ‘ENTER’ and hold buttons pressed simultaneously

But it would be just plain good luck, if your treadmill had firmware with the same secret menu... and it would be some really good luck if that menu could tell us anything useful.

So what is left? It might be you have to map out the circuit yourself.

Or look for pictures of similar things, e.g. an image search for

"circuit diagram for treadmill motor controller"


and see if any of those, kind of click. I mean if any of those are instantly recognizable as the same shape, same number of components, the same approach, used by your motor controller.


Reply 11 months ago

Thank you Jack, I've actually now removed 5 MOSFETs which are all dead. I've ordered new ones so I'll see how it goes.

I did find that service manual too, however those models are quite different from mine and don't have this function. I have a serial port, but I doubt I'll be able to get any software for it.

I'll try swapping the hardware, if that doesn't work I'll send it off to someone more skilled than myself. A new board is over £500 so I don't fancy that option :)

Thanks again

Jack A Lopez
Jack A Lopez

Reply 11 months ago

I wondered why the User's manual had that sense of urgency, imploring the user to, "immediately contact the dealer."

At first I was thinking they were worried the user might get fat and lazy, as a consequence of not being able to run on a working treadmill.

But, no. The true reason for the urgency is because there is money to be made, selling replacement controller boards.


Anyway, I hope replacing those MOSFETs makes it work.

Also, if you happen to discover a circuit diagram for this machine, or just for the output stage, the circuit that drives the motor, you can post that to this topic, or link to it, if you want to.

Somebody will probably want to see that.