Treadmill motor control board testing

[(*steve*)]

With power disconnected, use your multimeter on the ohms range to trace where the track connecting to pin 4 goes. Almost certainly it leads to a connector.

From there we need to look at the "small PCB"

 

[vocal]

pin 4 goes trough connector pin one and goes to small pcb with SMD components. then it goes to smd resistor 102. the other end or resistor goes to smd capacitor, goes back to connector pin 5 and goes to lm494c chip. other end of capacitor goes back to connector pin 3. connection between resistor and capacitor goes to pin 8, 11 and 12 of LM494c. Should I start drawing schematics for small pcb?

 

[vocal]

here you are. schematic for little pcb

 

[(*steve*)]

It would be interesting to know what is happening at pin 10 of the LM339 and pin 8 of the LM494

 

[vocal]

How do I check it? Pin 10 of the LM339 is negative input and pin 13 is output. However pin 13 of LM 339 goes to pin 2 of boards connector and is not connected to anythind on mcb

 

[(*steve*)]

Measure them with respect to the ground pin of the TL494

Essentially measure pins 8 and 9 of the TL494 with respect to pin 7. Oh, pin 12 would be useful too.

 

[vocal]

That will be difficult as mcb is mounted in not accessable place but I will try and post results in few hours

 

[vocal]

Pin 8 is connected to pin 12

Pin 8 and 7 of the LM949 shows 8.7vdc

Pin 7 and 9 shows 110mV

 

[(*steve*)]

That's interesting because pin 8 seems to be connected (via a 1k resistor) to the IGBT driver.

On the mosfet sriver's input you were seeing a low voltage, but you see a high voltage at the TL494.

Can you confirm:

1) this was while the motor was commanded "on"
2) the input pin of the IGBT driver was at a low voltage
3) there is a voltage drop (the difference between these 2) across the 1k resistor between pin 8 of the TL494 and the connector?

 

[vocal]

On motor on or off I have same readings
Pin 4 and 3 of mc33153p shows 7.9vdc
Pin 7 and 8 of lm494c shows 8.2vdc

 

[(*steve*)]

OK, so the LM494 doesn't seem to be pulling the level low.

It would be useful if you can find *any* signal on that interface to the small board which changes either when you tell it to start the motor, or alternatively when the error is asserted.

 

[vocal]

Only one visible thing happening, when motor switches on, is LED on mcb turning on. Also I can hear relay switching each time motor goes on or off. I will do some checks and post later on

 

[(*steve*)]

At this stage, we've traced back through the circuit some way and we still can't find the signal to turn the motor on and off.

We need to find something that is signalling the motor to be turned on and try to trace forward.

Clearly the signal stops somewhere!

 

[vocal]

What I spotted so far is that if I unplug 15vac the symptoms are exactly the same. All works but motor does not start. Will keep testing

 

[vocal]

If you have a look on drawings I have drawn in red, I found something really weird. Resistor R28. When I measure it it shows 1.7Mohm one way and whe I swap leads it shows 150kOhm dropping slowly to 42kOhm then jums up tu 70 and drops again. Also D2 and D7. They are N4004. On diode mode they show nothing even if I swap leads. I bought diodes and replace them but having same readings. I got 20 of them and even brsnd new have same problem. I was using amprobe multimeter and I thought it might be faulty so I tested same componentswith fluke 123 and having same results. It is really weird.
I tested also other components. I draw cap U4 on my drawings but that is actually voltage regulator 7815ct. It has 22vac input and 15vdc output so seems to be ok. From there I decided to test mc33153p ones again. Results are as follows
Pin 1 and 6 15vdc
Pin 1 and 5 0.3vdc
Pin 1 and 4 8.05vdc
Pins 1, 2, 3 and 8 are joined together

Will keep testing but I am running out of ideas.


Also talking about signal switching the motor on and off. I mensioned that if I switch motor on the LED switches on but I cannot find any connectin regarding this. I also checked voltage of tlp561g on pins 1 and 2 and getting 1.3vdc on motor on or off. I was wandering about pc817 but have no idea how to test it

And next weird thing. I said before that there is no voltage on motor pinouts on mcb when I switch motor on. Whe I disconnect the motor and switch it on, I am getting 300vdc on motor pinouts. I decided to check it again and put the probes to M- and R28 where R28 joints with C16 and Q4. I had 325vdc readings. That was measured with motor connected to mcb and pressed start button

 

[(*steve*)]

If you have a look on drawings I have drawn in red, I found something really weird. Resistor R28. When I measure it it shows 1.7Mohm one way and whe I swap leads it shows 150kOhm dropping slowly to 42kOhm then jums up tu 70 and drops again.

Readings below a resistor's value are nothing to be surprised about. It sounds like there's a capacitor nearby and you're seeing that charge up. Perhaps there is some active part of the circuit which turns on as the voltage rises to some point.

The resistance of 1.7M is only significant if the resistor is less than 1.7M. If the resistor is less than 1.7M, replace it.

Also D2 and D7. They are N4004. On diode mode they show nothing even if I swap leads. I bought diodes and replace them but having same readings. I got 20 of them and even brsnd new have same problem. I was using amprobe multimeter and I thought it might be faulty so I tested same componentswith fluke 123 and having same results. It is really weird.

sounds like you're doing something wrong.

Try reading the (new) diodes both ways on the resistance range. Do you have the meter leads in the correct sockets?

[/quote]I tested also other components. I draw cap U4 on my drawings but that is actually voltage regulator 7815ct. It has 22vac input and 15vdc output so seems to be ok. From there I decided to test mc33153p ones again. Results are as follows
Pin 1 and 6 15vdc
Pin 1 and 5 0.3vdc
Pin 1 and 4 8.05vdc
Pins 1, 2, 3 and 8 are joined together

Will keep testing but I am running out of ideas.[/quote]

All we're interested in at the moment are the signals running between the 2 boards. Do any of them change when you push the button (or whatever) to start the motor, or when the error shows up on the display?

Also talking about signal switching the motor on and off. I mensioned that if I switch motor on the LED switches on but I cannot find any connectin regarding this. I also checked voltage of tlp561g on pins 1 and 2 and getting 1.3vdc on motor on or off. I was wandering about pc817 but have no idea how to test it

And next weird thing. I said before that there is no voltage on motor pinouts on mcb when I switch motor on. Whe I disconnect the motor and switch it on, I am getting 300vdc on motor pinouts. I decided to check it again and put the probes to M- and R28 where R28 joints with C16 and Q4. I had 325vdc readings. That was measured with motor connected to mcb and pressed start button

I'm not particularly interested in this at the moment. It looks like power is switched to the motor circuit independent of the motor IGBT being turned on. It seems like you're seeing leakage across the IGBT. This matches the "I see voltage without the motor but not with the motor" symptom.

 

[vocal]

I was examinig mcb and have no idea what could cause the problem. So far I can say that there is 3 different power sources powering whole machine. 12Vdc - powers upper pcb with buttons and display, 15Vdc powers mcb part responsible for motor control, 240Vdc - powering motor.
There is only two common parts between two sections of mcb. First one is relay which turnes BR3510L on and powers motor with 300vdc. - that was the click I could hear when I was pressing start button. Second component is optocoupler PC817 but no idea what it does. I was wandering how come you can set/control the speed of the motor?
I think I will draw remaining schematics for mcb. Maybe that will explain a little bit more

 

[vocal]

Here you have drawings for whole mcb. I think that optocoupler PC817 is causing the problem or something what drives optocoupler but I do not know how to trace it. What do you think guys?
I unsoldered PC817 and wandering if I can connect mcb and test machine but I am afraid I will blow something without having PC817 in
...
Tested voltage regulator 78L05. I have 4.2vdc between ground and input. When I switch motor on it drops to 3.5vdc. Output shows 6mV and it jumps up to 60mV when I switch the motor on
I am a little bit confused between input and output, which one is which one, as different websites show different data.


...
Just found PC817 on upper board used for heartbeat rate and swapped it. No change. Heartbeat monitor works and motor is still dead so opto isolator is ok. I thought that maybe PC817 has short.


.....

ok, finally I found something I think
First of all my lack of electronic knowledge lead me to think that all of the little black components were transistors and I was wrong. So, I had to change drawings a bit.
Second thing is that I was testing transistor instead of voltage regulator.
Resuming, 78L05 kicks out 5Vdc so everything seems to be ok on that side.
I found another 'transistor' 78L12 and that seems to kick out 7.2Vdc.
If you have a look on the schematics, does it makes sens now or not really?

 

[(*steve*)]

78L05 is a 5 volt regulator and 78L12 is a 12 volt regulator. The outputs should be 5 and 12 volts respectively and the inputs need to be significantly higher (preferably at least 2V higher).

A 78L12 should have 12V on the output and it has 7.2. What is the voltage on the input? If it's above 14V, the regulator is perhaps failed. But is it hot? These regulator will shut down if they get too hot (generally caused by the circuit following it drawing too much current)

Some of your circuit diagram makes no sense at all, and clearly you've failed to see some connections and shown others incorrectly. As an example, the emitter of the IGBT *MUST* be connected to the high voltage power supply somewhere, and whilst you sometimes see an SCR across a power supply, I very much doubt that it would be in this case. (in fact I have been working on the assumption that the cathode of the SCR connects to the Emitter of the IGBT.

Your diagram doesn't show the inputs or outputs of the regulators, but it appears that the 78L12 is fed from the 78L15. So the input voltage of the 78L12 should be 15 volts. If it is not, you need to go back and look at the 78L15.

 

[vocal]

I posted results earlier when tested 78L15 it has 22Vac inpu and 15Vdc output so 78L12 has 15Vdc input but kicks out 7.2V. Is it faulty?

Regarding IGBT I did not missed any connections ans all pinouts seem to be correct as checked on alldata website