Hi, new member trying to repair a Jazfit T45 treadmill that I picked up for free. I am somewhat experienced at troubleshooting and repairing some electronics, but nowhere near being an engineer. Thanks to anyone who can help.

Fault description: no belt movement. When the start button for belt movement is pressed, the relay on the power control board clicks. Manually moving the belt at this time doesn't help it get going. The belt moves freely manually, and the motor runs the belt fine using an external DC source. Control console and motorized incline both work fine.

Output to motor reads ~3VDC when the start button is pressed. The LED near the large capacitor glows at around half brightness whenever the main power is turned on.

I haven't been able to locate the manufacturer, and a replacement board seems to be unavailable. Schematic is also unavailable, but I will draw one out from the board if I have to.

Aside from replacing the large capacitor, I've targeted the output components first ... advice is welcome though if other components are known to cause problems.

Referring to the pictures below, my biggest problem is identifying and sourcing some of the components attached to the heat sink (edit: the middle one was unsoldered in the picture if you're wondering). The one on the left shouldn't be too hard; information seemed fairly easy to find for it, but comments about it are of course welcome.

I ~think~ the G80N60 in the middle is the same as this. If so, then I have a source for that one. If there might be issues, please let me know. The one in the link is an IGBT, which I don't believe I have the tools to test, but it's only $11 so I'm willing to spend that anyway.

The last one on the right is the sticky one. Nobody here in Australia seems to be able to reference it. The datasheets seem to match(?) but I don't know how to find any equivalents, other than perusing data sheets for compatible specs. If that's what I need to do then I might have to do it, but does anyone here have any better ideas?

Thanks again for any help. I'll aim to stick around and offer the community any help I can after this.

nice work man..............

 

Where has everyone gone??

The treadmill went to the kerbside cleanup but I salvaged the motor, power electronics and gas struts. Now I have had a chance to have a close look at the main board and the miniboard. I took some macro pics of the mini board with a view to tracing it out but when I zoomed in on the PC I found the surface mount resistor R27, 100 ohms, adjacent to pin 9 was obviously fried. Someone has tried to erase the IC labels but I can just make out that U1 is LM339 but I cannot read anything useful from U4 or U2.

Pokethebear, what do you see if you look closely at that R27 on your miniboard?? Can you help with the labels of U2 or U4??

I have cleaned everything and replaced R27 and now I have to work out how to test it without the console.

A bit more tracing around the connector to the console shows that pin 7 is the tacho feedback, pin 9 is not connected and pin 10 is the incline angle sensor signal. So the only connection from the console to the motor control is from pin 5 of the console connector through the opto U6 and the delay/filter network to pin 4 of the miniboard. As the signal is heavily filtered it seems that it should be possible to control the motor with a variable DC voltage, the console probably outputs a PWM signal but this is reduced to an average DC by the delay/filter network. The actual PWM for the motor must be generated by the miniboard.

I think that I have been wasting time trying to test without the motor connected. I am hoping that connecting the motor will overcome my problem of how the U1 opto is turned on. Without the motor when I turn RY1 on and apply 240VAC to the big bridge rectifier all I get is a faint glow from LED1. There is 7V at the motor + terminal so about 0.1mA through the LED. My theory is that with the motor connected this is enough to turn on Q4 and this will turn on U1 and I will get the full 300VDC on the motor + terminal and I should see LED1 light up brightly with 300V / 68k = 4.4 mA. Then I will try a pot between pins 4 and 3 of U6 and see if the motor runs.

Any comments??

R27 not well.jpg

 

Interesting. Reading the fine print I noticed that U1 has a zero-crossing detector built in. I was trying to trigger it by putting 1k across Q4 C to E after I had energised RY1. No result. When I put the 1k across Q4 first, then turned on RY1, bright LED!! Will try with the motor connected tomorrow.

 

More component values:
R24, 0.056 ohms, 5W current sense resistor
C12, 470 uF, 400V

 

Feel like I am talking to myself here.

Switching on RY1 and putting a 1M resistor across pins 5 and 6 of the console connector I can see PWM pulses on pin 1 of the miniboard at 16kHz, duty cycle varies slowly from low duty cycle to high allowing for the inversion through U9, MC33153.

I have had the motor running but only with fooling it by shorting Q4 C to E briefly to turn on the SCR Q2 via opto U1. Once on it latches and I can start and stop the motor with a signal on pin 5 of the console connector.

What do I have to do to get the SCR to turn on by sending a signal on pin5 of the console connector???

 

Are u still trying to fix the board ?

 

Still working on it. I can only make it run by shorting Q4 C-E. After that everything works fine.

More information. I used the ask a friend option and he has worked on servicing DC motor controllers a long time ago. He mentioned that some of the points I had been measuring with a meter would probably have pulses on them. I got out the scope but without an isolation transformer I can only use it without the GND lead making it AC coupled. Have ordered an isolation transformer, will arrive in the next couple of days.

Sure enough, Pin 6 of the miniboard has very brief pulses at 16 kHz on it! Present theory is that Q4 is protection against the IGBT switch Q3 latching or failing as a short circuit. If there are no positive pulses on Motor_- then Q4 turns off and disconnects the HV by turning off SCR Q2 through opto U1. To get the thing started pulses are provided from miniboard Pin 6 but these are very low duty cycle so even with Q3 latched they will not provide significant output. Will get details of the level and timing of these pulses after I get my new isolation transformer. These pulses are not turning Q4 on, have checked Q4.

I now think the zero-crossing of opto U1 is not an issue.

 

There is a sequence issue! You have to turn on RY1 before applying a speed signal to Console connector Pin5. Of all things I found R28 was open circuit with no visible sign of damage?? Replaced it and turned the speed signal off and I get bright LED1 when I turn RY1 on, at last. All this is on the bench in my office, will try with the motor connected next.

 

Same friend who used to work with motor controllers now designs and manufactures electric fence equipment. He has seen metal film resistors fail by going open circuit when subject to medium level pulses even when they are well within their rating.

It would be great to hear if any of this helps Pokethebear get his treadmill working. As my kids would say "He started it"

 

It works fine with the motor!! There does not seem to be a sequence required, if I don't turn the speed signal down and turn the relay on and off, the motor gives a kick as it tries to accelerate hard. Normal accel and decel are very slow, guessing they are limited on the miniboard.