MC-66 Speed Controller

Thread Starter

Rutts55

Joined Feb 10, 2016
4
Hi All,
first post so please be gentle. I have a treadmill. Proform 525EX manufactured by ICON. It was left in house I recently moved to. Non-running so I investigated as to why. Power gets to the treadmill fine. The safety key works as the incline works and then stops when the safety key is removed. However the belt won't run. On further investigation I found the speed controller shot. The board had a label which says MC-66 but the actual board is a MC-65. I trawled the net and found a few threads on these boards but they don't answer my questions. I've been trying to find a schematic with no luck. Although some of the construction is similar to the MC-60 which help me construct the part schematic I have attached of the power section.
There were a couple of components physically blown ( the S8020L, D8020L and one of the 470uf Caps) which I replaced. When I power the board now I don't get any LED's lit. I've tested the LED's and all appear OK apart from the SCR TRIG which fell apart when I was testing it. So questions are:
  • Where can I source a replacement LED as I don't know the value or part number?
  • When the board is connected I can't find 12v anywhere on the board. From the schematic should I be seeing 12v around Zener D3?
  • When testing for the 12v what should I be testing too? GRD or AC1/AC2?
When I test for 12v I'm getting around 120v but not sure if I'm testing correctly. I've tested all of the transistors and they seem fine as do the straight diodes I've tested.

It's a long time since my college days of working electronics so I'm a tad rusty but can remember a lot of the theory so any pointers would be massively helpful.

Thanks in advance

Paul
 

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Dodgydave

Joined Jun 22, 2012
9,457
Your drawing is wrong C16 C17,

i would use D13 Anode,C16,17-ve as the common 0V terminal, you will get the 12v across the zener if D2, R2,R3 are ok,

any 2mm red led will do as its in series with the scr opto.
 

Thread Starter

Rutts55

Joined Feb 10, 2016
4
Thanks DD. Thanks for pointing out the typo. I'll purchase myself some LED's and repair the circuit. As far as I've tested so far D2 and R2/3 are OK.. I'll reconnect it and see what results I get.
 

Thread Starter

Rutts55

Joined Feb 10, 2016
4
Thanks again for the replies. I went and re-tested. I had no voltage at coming out of D3. I have now tested R2 and R3 and found one of them blown. Hence my lack of 12volts. I'll order myself some resistors. All ready ordered the LED's. So hopefully with everything else I've renewed it'll be a goer.

The treadmill had been kept in damp conditions (the pulley on the belt drive is very rusty) so I'm guessing this either didn't help or was the cause.

If I replace them and I'm still stuck I'll tap you up for more assistance if that's OK?

Thanks again.
 

view63

Joined Feb 12, 2020
5
hello does anyone know what the value or kind is diode #11 , it seems open but there is no marking on it

the motor does not function at all

please help

thank you
 

view63

Joined Feb 12, 2020
5
Most of the MC6x series were similar, here is the mc-60.
Max.
hello sir

maybe you can help me - on the mc-65 \ 66 there is a diode #11 but there is no markings on it , i am not sure if it's a diac \ zener \ silicon diode \ Ntc.

the markings on the board is D11

thank you
 

view63

Joined Feb 12, 2020
5
the motor does not start .
all the leds are lit ok , the motor that move up and down does work.

the D11 has no markings , it does not have any reading of resistance or in diode mode.
like its open . but it looks like and NTC but the marking on the pcb is D11

the D11 go to a resistor that connect to pin #4 in the oprocoupler IL420.

thank you
 

MaxHeadRoom

Joined Jul 18, 2013
21,425
, it does not have any reading of resistance or in diode mode.
like its open .
You didn't happen to test it on resistance range by any chance?
A diode will only read as one correctly when forward biased, using the diode test range if your meter has one.
Max.
 
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