My old treadmill (Proteus MTM 650) suddenly went to full speed and won't slow down.
The safety magnet does not make it stop.
I completely disconnected the top board with all controls and display - it keeps running at full speed without it.
The main switch on the bottom does turn it off. When switching it back on it immediately makes a bit of electric/sparks/static noise, and the motor goes to full speed.
I cannot see any visual damage on the top or bottom boards.
When folded, laying on its side, open - the motor did not spin, but it did make some hum noise for a few seconds. I think it is just caught somewhere, so I shortly turned it off.
It is an old model, maybe 15 y/o, and has no programs. The incline is electric, but seems to be separated from the rest – it is only connected to a switch on the top board, that I also disconnected.
The only other link from the top board to the bottom is an Ethernet shaped connector.
What is wrong? Can it be fixed affordably? When you say Motor Controller do you mean the entire bottom board?
The local service providers no longer have spare parts for it. I tried asking the manufacturer for schematic and part, but got no reply, yet.
I know basic electronics and have some basic gear.
I took some photos, let me know if you need more.

Thanks in advance for any assistance!

 

Try the two 3 pin silicon blocks ( transistors or thyristor) on the heatsink, possibly shorted out.

 

Thanks Dave. Are you referring to the two at the top, outside the circuit board? - One of them seem to only have 2 pins.
Do you think it could only need resoldering or do I need to replace them?

 

Yes those , the 2 pin is a diode, try the 3 pin for shorts.

 

Appears to be a PWM board, hence large bridge and electrolytic cap.
Is there any part No. on the board? It may be worth changing the Mosfet for the cost.
Normally most T.M. controllers will not allow the motor to turn unless the speed control is at zero.
So if it takes off immediately usually points to the mosfet.
Max.

 

The right pin seems connected to its right, to the middle pin and to all connectors beneath it.
The left pin, I have no idea what it is connected to.
What should I do?
Thank you both! Max, I will check.
I have add close-ups from both sides.

 

The left pin maybe connect to a trace on the reverse if it is a double sided board.
Couldn't find anything on that Mitsubishi Part No.
Max.

Oh I see you posted the reverse side so that is ruled out.

 

Looks like the base or gate is the left pin, the emitter/source is the right pin,

measure the resistance of the centre pin to each other pin

 

Max, I could find no longer number on the board than the 1025. There's also "Ltd." Peeking from beneath the large capacitor, that looks glued. I couldn't find that part number either.

Dave, center to left pins (and right to left) is 149 Ohm. Center to right pins takes a few seconds to stabilize at around 1 Ohm.

 

looks like its a shorted transistor, can you unsolder it and test again

 

I'll try in the morning. So the transistor or its soldering is bad anyway? I mean, I won't be adding another fault if I have no idea what to later connect the left pin to?

 

if its shorted out then its damaged, and will need to be replaced.

 

Yep, shorted FET or IGBT driver, and also cheeck that Kickback diode next to it onthe heatsink, they often die together.

We must know the operating voltage for the tread to advise a replacement, but replacements are available, 120vac Treads will have a 200v(prv), 30 to 75A switching device, either IGBT or HexFet

220v treads will have a 400v(prv) 20-50A switching device ;o)

 

Thank you Jatinah. It's a ~230V treadmill.
I was forced to take a break from fixing it, but I'll get back to it in a couple of weeks.
How should I find what parts to purchase?

 

Hi There,

I might consider the Vishay Siliconix SIHG25N40D-E3 (or -GE) depending on what is available for you where you are. If you are near the UK you can email a friend over there who may also be able to help source a replacement and help advise you, his name is Tim Jennings and I recall an email of treadmilldoctor1ATyahooDOTcomDOTuk

Check the kickback diode next to it, as many times if that Mosfet/TrenchFet/HexFet or IGBT rips/shorts, it will often take out the diode which is critical to the switching scheme. Also check Gate Drive resistor to that FET to make sure it hasn't fried. That FET should have a pull-down resistor on the Gate-to-Ground leg of 1k ohm or higher, and a Series Gate limiting resistor of say 22 ohm up to 470 ohm but not much higher. If gate resistor is toast, there is more trouble upstream to check for.

Looking at the photo, the leftside lead is the Gate, center lead is (+) Drain, right lead is (-) Source. While you are in there with a soldering iron, consider replacing the 5 electrolytic capacitors in the onboard power supply to shore things up there, and the main storage capacitor appears to be ok, with no doming, swelling or heated/shrunk plastic jacket.

Take your time reworking, and remember, RHoS or Lead-Free solder has a high melting point, over 750f and electrical grade rosin flux is your friend during rework, after it can be cleaned with 99% alcohol and dabbed off.

Good Luck!

 

Thank you for the detailed reply! I will definitely try that when it is possible for me.
My solder though is quite old, so I don't believe it is Lead-Free. I also have an old brown paste that is called "soldering paste with kleentin" and was used at the time by professionals for better soldering, not for surface mounted components and with no other "flux". I see no tin balls inside and I'm not sure if it's an old name for flux. Do I still need flux? Do I need to replace any of them? How do I know which to purchase? - I don't need much and don't wish to invest too much in something that would not be used. I only do a small solder repair about once a year or less.

 

Hi There,

For your own repairs, regular Tin/Lead(63/37) solder with a rosin core would work fine. The flux you talk of doesn't ring a bell with me for electronics work, but may be good for pipe sweating and soldering, but that is not the same flux material. I use the Radio Shack flux that comes in a white plastic jar, and there are small tubes available for hobby folks, try a search on electronics soldering flux, rework flux, "Tacky Flux" and you should find the flux around. Solder is also cheap if you grab a small coil while getting flux, and try to keep the solder gauge thin, I tend to steer towards .015" Diameter solder.
Soldering techniques should be careful as to not keep any Lead/Point/Trace heated for longer than 10-seconds, and remember the "3-Second" Rule...if the solder hasn't flowed nice and smooth in 3-seconds(with "wetting" to both pad surface and lead), there is something wrong, remove heat and try pre-heating the PCB with a hair dryer right before rework to start with warm fiberglass PCB. Good Luck!