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Old 08-21-2018, 10:19 AM   #21
R_J
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Default Re: Treadmill DC Circuit no motor start

The speed control should vary the voltage on LG2 from 0 - 5 volts, If it is connected to pin 3 of U2 I would expect more than 0 volts on that pin. You need to check the resistance between LG2 and pin 3, (buzzed has no value) is it 0Ω
Do you still have 5 volts on LG1 if you do, you should have ie: 2.5 volts on LG2 with the speed control set to the middle.

You said you shorted pin 3 & 4 and the motor ran full, that tells me if there is a higer voltage on pin 3 the circuit should work. That slipp of the probe may have also damaged the speed pot, so check its resistance through its full range
R5 is should be a minimum or maximum speed set, likely sets motor stop when speed control is at minimum.

Now with the new voltages and the top of the ic not looking like it is damaged, the ic could be ok.
From post #13
Quote:
Originally Posted by davg View Post
RJ the voltage between LG3 & LG2 do vary as the speed control is turned and it is in the 0 - 5 range.
Where is the speed control set when you are checking these voltages?

Last edited by R_J; 08-21-2018 at 10:47 AM..
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Old 08-21-2018, 01:14 PM   #22
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Default Re: Treadmill DC Circuit no motor start

[QUOTE=R_J;846052]The speed control should vary the voltage on LG2 from 0 - 5 volts, If it is connected to pin 3 of U2 I would expect more than 0 volts on that pin. You need to check the resistance between LG2 and pin 3, (buzzed has no value) is it 0Ω
Do you still have 5 volts on LG1 if you do, you should have ie: 2.5 volts on LG2 with the speed control set to the middle.
You said you shorted pin 3 & 4 and the motor ran full, that tells me if there is a higer voltage on pin 3 the circuit should work. That slipp of the probe may have also damaged the speed pot, so check its resistance through its full range
R5 is should be a minimum or maximum speed set, likely sets motor stop when speed control is at minimum.
Now with the new voltages and the top of the ic not looking like it is damaged, the ic could be ok.
From post #13
Where is the speed control set when you are checking these voltages?

[QUOTE=R_J;846052]The speed control should vary the voltage on LG2 from 0 - 5 volts, If it is connected to pin 3 of U2 I would expect more than 0 volts on that pin. You need to check the resistance between LG2 and pin 3, (buzzed has no value) is it 0Ω
It is 0Ω

Do you still have 5 volts on LG1 if you do, you should have ie: 2.5 volts on LG2 with the speed control set to the middle.
Still have 5V on lG1 and yes 2.5V on LG2 set to middle

You said you shorted pin 3 & 4 and the motor ran full, that tells me if there is a higer voltage on pin 3 the circuit should work. That slipp of the probe may have also damaged the speed pot, so check its resistance through its full range

From soft start (Reset 0) to Full using Red and White wires 10.7K to 1K

R5 is should be a minimum or maximum speed set, likely sets motor stop when speed control is at minimum.
Yes I can vary the voltage on LG2 Higher than 5V lower than 5V with R5

Where is the speed control set when you are checking these voltages?
The Speed Control was set at 0.
Halfway the voltages on pins 1-7 change as follows
1-10.1
2 -0.5
3 -2.32
4 -11.3
5 -4.5
6 -1.0
7 -10.1
Pins 8-14 no change

Last edited by davg; 08-21-2018 at 01:20 PM..
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Old 08-21-2018, 02:09 PM   #23
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Default Re: Treadmill DC Circuit no motor start

When you vary the control I suspect that pin 1 and pin 7 of U2 also change.
There is a point marked LD2 (SCR Trig) is there any voltage on that point? and does it vary with the control? This may or may not be a dc voltage but might actually be a pulse.
Pins 12-14 of U2 may not be used, pins 8-10 seem to set the 5 volt level.
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Old 08-21-2018, 08:17 PM   #24
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Default Re: Treadmill DC Circuit no motor start

0.0V on LR2 and does not vary with the control but 11.3V on one side LR1. I'm seeing 54V on one side of D9 & D10 but 0.0V on either side of D-8 is that normal. It appears that the board is working but what is stoping the circuit from starting the motor?
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Old 08-21-2018, 09:00 PM   #25
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Default Re: Treadmill DC Circuit no motor start

You lost me, I don't see LR1 or LR2.
LD2 test point is what turns on the led inside of U3, but like I said it is likely a pulse but there should be some dc on it I would think (or try measuring a/c volts on that point and vary the speed control and see if there is a change)
When you measure voltage from ground to either of those diodes you are measuring aprox 1/2 the (120v) line voltage
The diodes and the scr's form a bridge circuit that will change the 120v a/c into a pulsed aprox 90vdc for the motor
U3 Is the scr gate driver, it is an opto isolated device, It has an internal led that is pulsed by a signal that likely comes from U1.
U2 is used to control that pulse which controls the motor speed.

The 2 diodes D3 & D4 rectify the a/c and feed R2 which drops the voltage down to 12 volts which is regulated by a zener diode ( 1n4742A)
Quote:
6) If I jumper center leg and right leg of Q4 motor will run?
doing this may have damaged U3
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File Type: pdf S_110_MOC3052 SERIES-337181.pdf (453.3 KB, 2 views)

Last edited by R_J; 08-21-2018 at 09:41 PM..
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Old 08-22-2018, 06:40 AM   #26
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Default Re: Treadmill DC Circuit no motor start

Quote:
Originally Posted by R_J View Post
You lost me, I don't see LR1 or LR2.
LD2 test point is what turns on the led inside of U3, but like I said it is likely a pulse but there should be some dc on it I would think (or try measuring a/c volts on that point and vary the speed control and see if there is a change)
When you measure voltage from ground to either of those diodes you are measuring aprox 1/2 the (120v) line voltage
The diodes and the scr's form a bridge circuit that will change the 120v a/c into a pulsed aprox 90vdc for the motor
U3 Is the scr gate driver, it is an opto isolated device, It has an internal led that is pulsed by a signal that likely comes from U1.
U2 is used to control that pulse which controls the motor speed.

The 2 diodes D3 & D4 rectify the a/c and feed R2 which drops the voltage down to 12 volts which is regulated by a zener diode ( 1n4742A)
doing this may have damaged U3
Tks R_J sorry that should have read LD 1 & LD 2 and I appreciate the theory. My big draw back is I don't understand the theory?
If U3 was damaged through testing Q4 or Q3 it wouldn't be a new problem as it occurred after the initial break down but it do sound like a point of concern since it looks like the board is not getting that signal to turn on that side of the circuit to U2?
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Old 08-22-2018, 10:16 AM   #27
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Default Re: Treadmill DC Circuit no motor start

Looks like there is 67VAC on LD2 measuring from LG5 or chaise ground
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Old 08-22-2018, 11:10 AM   #28
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Default Re: Treadmill DC Circuit no motor start

LG5 is not chassis ground. LG5 is 120 volt A/C input. The only ground point to check voltages on points like ld2, u1 u2 etc. is LG3, this is ground.
The way to check this circuit is with a oscilloscope, there are pulses created by the circuit that control the optocoupler, these pulses can not be measured using a multimeter.

When you removed these parts from the treadmill and tried them on the bench, did you use the cables etc. from the treadmill (the cables from the control panel to the speed control board) or did you make up cables?
Something must have been connected improperly and damaged something.

Last edited by R_J; 08-22-2018 at 11:30 AM..
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Old 08-22-2018, 07:19 PM   #29
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Default Re: Treadmill DC Circuit no motor start

Quote:
Originally Posted by R_J View Post
LG5 is not chassis ground. LG5 is 120 volt A/C input. The only ground point to check voltages on points like ld2, u1 u2 etc. is LG3, this is ground.
The way to check this circuit is with a oscilloscope, there are pulses created by the circuit that control the optocoupler, these pulses can not be measured using a multimeter.

When you removed these parts from the treadmill and tried them on the bench, did you use the cables etc. from the treadmill (the cables from the control panel to the speed control board) or did you make up cables?
Something must have been connected improperly and damaged something.
Tks again RJ. Using LG3 as ground there is no voltage AC or DC on LD2

Yes all original wires were used on the bench test just as it came off the treadmill.

Some DC voltage checks on U3 using LG3 as ground are as follows;
Pin 1- 0.003
Pin 2 -0.005
Pin 3 -0.007
Pin 4 -164.4
Pin 5 -153.0
Pin 6 -0.00
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Old 08-22-2018, 08:29 PM   #30
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Default Re: Treadmill DC Circuit no motor start

You can only measure pins 1 & 2 with reference to LG3 ground, pin 3 is not used,
pins 4 connects to D5 cathode, so I suspect it would measure 160vdc. pin 6 connects to the scr gates, pin 5 is connected to the ic substrate.
Remember U3 is an optocoupler, pins 1,2 are isolated from 4,6.
Basically U1 produces pulses that turn the led in U3 on and off. those pulses are transfered internally to the optical divice connected to pins 4&6 which in turn pulse the scr gates, the scr's then supply pulsed dc to the motor
U2 controls the duration of the pulses and that changes the speed.
LD2 connects to R21 and goes to U1 (pin14 maybe?)

This I believe is the output part of the circuit, pin 1 pf U3 goes to LD2 and the rest of the circuit (I am not tracing it out)

When you measure the voltage on U2 pin 1 and vary the speed slider, does that voltage also vary ?
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File Type: pdf MC-02_output.pdf (66.1 KB, 1 views)

Last edited by R_J; 08-22-2018 at 08:54 PM..
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Old 08-22-2018, 08:46 PM   #31
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Default Re: Treadmill DC Circuit no motor start

Tks R_J truly appreciate your help. I will have to take it to a Tech Shop that has some proper equipment or (cheapest option) just look around more yard sales for another unit
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Old 08-23-2018, 06:13 AM   #32
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Default Re: Treadmill DC Circuit no motor start

Quote:
Originally Posted by R_J View Post
You can only measure pins 1 & 2 with reference to LG3 ground, pin 3 is not used,
pins 4 connects to D5 cathode, so I suspect it would measure 160vdc. pin 6 connects to the scr gates, pin 5 is connected to the ic substrate.
Remember U3 is an optocoupler, pins 1,2 are isolated from 4,6.
Basically U1 produces pulses that turn the led in U3 on and off. those pulses are transfered internally to the optical divice connected to pins 4&6 which in turn pulse the scr gates, the scr's then supply pulsed dc to the motor
U2 controls the duration of the pulses and that changes the speed.
LD2 connects to R21 and goes to U1 (pin14 maybe?)

This I believe is the output part of the circuit, pin 1 pf U3 goes to LD2 and the rest of the circuit (I am not tracing it out)

When you measure the voltage on U2 pin 1 and vary the speed slider, does that voltage also vary ?
When you measure the voltage on U2 pin 1 and vary the speed slider, does that voltage also vary ? Yes with slide halfway reading about 10 VDC
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Old 08-23-2018, 09:19 PM   #33
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Default Re: Treadmill DC Circuit no motor start

Ok, so the voltage does't vary with the control it just stays at 10v.
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Old 08-23-2018, 09:46 PM   #34
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Default Re: Treadmill DC Circuit no motor start

Disconnect all power, and remove the three leads going up to the pot. Check the pot.

From black to red, I'd guesstimate 1-10k for the element, maybe as high as 25-50k.
From white-black, 0 full CCW, increasing towards CW.
From white-red, full resistance (the element) CCW and decreasing towards CW.

None of these should be open. If so, check leads especially at the pot. And/or soldering if leads/pot terminated on a PCB.

Give trimpot R5 a shot of control cleaner and rack it a few times. Put it back where it was afterwards.

There's probably a resistive divider pulling the wiper pin on the control PCB up to 10V; this not changing does not condemn the control until the pot is ruled out first.

You can also substitute another pot with a direct connection to the control PCB. This, or you, need to be isolated while adjusting to see if the motor runs- "common" on that PCB floats at 1/2 line voltage via the rectifier. The main hazard is not shock; it's backfeeding and damaging components if you make connection between any of them and a grounded object. There is ~60VAC present in common mode between anything on that board and grounded objects. At the non-isolated TRIAC side, full line voltage is present.
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Old 08-24-2018, 06:16 AM   #35
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Default Re: Treadmill DC Circuit no motor start

Quote:
Originally Posted by R_J View Post
Ok, so the voltage does't vary with the control it just stays at 10v.
As indicated in post 32 the voltage do vary with the control. It varies from 0 - 10 to the halfway position.
The pot checks out OK I swapped it out to another unit with a MC 60 board which has the same connections and it works?? The motor also checks OK when connected to this MC-60 board?? so the fault is diffidently with the MC-02 board.

Last edited by davg; 08-24-2018 at 06:33 AM..
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Old 08-24-2018, 11:23 AM   #36
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Default Re: Treadmill DC Circuit no motor start

Ok, so the voltage on U2 pin 7 does it also vary? Pin 7 connects to R27 which then connects to Q2. Check U1 pin 12, What is the voltage here and does it vary with the speed control?
Can you provide the numbers on Q1 & Q2?
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Old 08-24-2018, 02:34 PM   #37
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Default Re: Treadmill DC Circuit no motor start

U2 pin 7 do vary just a small bit from 0.002 to 0.014 full across. U1 pin12 reads .002 to 0.43 full across?
The numbers on Q1 2N4406-310 and Q2 is 2N4401-011
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