MC-66 Speed Controller

Discussion in 'General Electronics Chat' started by Rutts55, Feb 20, 2016.

  1. Rutts55

    Thread Starter New Member

    Feb 10, 2016
    4
    2
    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
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,967
    744
    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.
     
  3. Rutts55

    Thread Starter New Member

    Feb 10, 2016
    4
    2
    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.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,500
    2,366
    Most of the MC6x series were similar, here is the mc-60.
    Max.
     
  5. Rutts55

    Thread Starter New Member

    Feb 10, 2016
    4
    2
    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.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,500
    2,366
    This is a little more on the MC-60 incl a mod but the first part is from the manual.
    Max.
     
  7. Rutts55

    Thread Starter New Member

    Feb 10, 2016
    4
    2
    Hi,
    Just a quick report back. I just received and fitted the resistors I ordered. Tried it and the tread mill lives again. Thanks for all your help. Appreciated.:D:D:cool:
     
    Dodgydave and MaxHeadRoom like this.
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