Treadmill motor control board keeps blowing fuse

Discussion in 'Technical Repair' started by zariq, Apr 4, 2016.

  1. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Hello every one.

    I am hoping to get some advice about a treadmill motor control board which blows the internal 10 amp fuse
    as soon as it's turned on. The display console and incline is working but the belt doesn't move when increasing
    the speed.

    After the first time, I replaced the fuse and it too blew. I checked the board and noticed that the 3 ohm
    current limiter(NTC 3D-20) had a crack and it's resistance was 6 ohms. I replaced the fuse and disconnected
    the motor and all plugs going out of the board. This time the fuse didn't blow, but the circuit breaker tripped.
    The current limiter had a small chunk of casing blown off and the resistance has gone up to 9 ohms. On the
    bridge rectifier(KBPC1510) two diodes are fine and two are coming up as shorted.

    I decided to desolder the mosfet(IRFP460C) to check it. Unfortunately the desoldering didn't go too well. After
    destroying two soldering bits and one hour of leaning over the board, frustration got the better of me and the
    board recieved a whack with pliers, with the intention of rendering it unserviceable, and leaving me free to move
    on. Just for good measure I also gave the rectifier(F10u60DN) a tug as well. After a visual inspection, there doesn't
    seem to be any physical damage. I am resigned to having to throw it away but couldn't without giving it one
    more try.

    What I would like to ask is:

    1. The mosfet is obsolete. Which properties are the most important to consider for the replacement?
    2. Would 2.5 ohms or 4 ohms be ok for the current limiter or does it have to be 3 ohms. Having trouble locating 3 ohms?
    3. According to listings on amazon the bridge rectifier is half wave. Is this the reason two diodes on the board are showing as
    shorted and there is nothing wrong with it?

    Thank you for reading.

    P.S.
    It would rightly appear to some as an overreaction on my part to a failed desoldering attempt. The failure to remove the mosfet
    was just the last straw. Electronics has been a love of mine since the age of ten. Now in my early forties and after countless
    hours spent in libraries, lots of money spent on buying books and all those hours on Youtube has not resulted in much understanding
    of the subject. I can tell from experience that not understanding something you like is very frustrating.

    Sorry for the long post.
     
  2. Deamon73

    New Member

    Apr 22, 2016
    2
    0
    Hi did you have any joy repairing this I've the same board and looking for a schematic my mosfet blew and took out R2 and don't know what value resistor to fit
    I sourced a mosfet on eBay
     
  3. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Hi Deamon73,

    I believe that is 62ohm 1/2watt. This is the Gate-Drive limiting resistor for the PWM drive signal coming from the small board hidden inside that metal housing. If the current thru this resistor fried it up, I would suspect there may be trouble inside that metal shielded box which holds the PWM logic controls.

    So, if you were to replace that MosFet/HexFet and resistor, and be sure to check that kickback diode next to it, you may find the very same result at power-up or Start. When I find the gate resistor smoked, I usually also find a push-pull transistor set ripped further upstream ;o)

    Good Luck
     
  4. dacflyer

    Member

    Nov 19, 2010
    13
    0
    the bridge rectifier you speak of is actually a full wave rectifier, if your reading any shorts on that part then it is BAD.

    good luck
     
  5. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Correct....the bridge is FULL WAVE ;o) Any Bridge you find with four leads can be assumed to be full wave or contain 4 diodes.

    Looking at the pics and reading a bit more, the IRFP460 tells me this is a 220vAC treadmill. This control board is used in Trimline units and that Thermistor can be replaced with any thermistor capable of 30A constant like the SL32 as long a the cold resistance stay below 4ohms or so. The thermistor will reduce it's resistance when it warms up, but must also pass all motor current which is a set back. The original bridge is quite beefy I thought, maybe 35 or 50A device?

    ;o)
     
    Last edited: Apr 22, 2016
  6. Deamon73

    New Member

    Apr 22, 2016
    2
    0
    A big thank you to everyone I will be having a attempt tomorrow with this and will post back just a quick question does anybody know what is the correct fuse rating for this board
    Tia
     
  7. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    I have a slightly different model by that same manufacturer made for 120vac with a "Main" fuse of 18A Slo.
    If you are running a 220vac unit, that "main" fuse may be lower due to the higher voltage, say more like 10A-15A.
    Careful....
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    The OP shows he is from the UK so 230v , @Deamon73 does not indicate his CoO so anyone guess?
    In N.A. 15amp is the basic outlet capacity for residential equipment.
    Max.
     
  9. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Hi All.

    Thanks to everyone who has replied. After a few weeks of nothing, I wasn't expecting any posts now.
    In reply to to Deamon73, yes I did somehow manage to get it working with what you might call brute force.
    I replaced the the bridge, the current limiter, the mosfet and the F10U60DN diode. The fuse on the board is a 10 amp slow blow(U.K.).

    The thing that confused me about the bridge is that a lot of listings on Amazon mention that the KBPC1510 is half wave rectifier.
    The bridge on the board is 15 amps 1000 volts and is tiny. I replaced it with a 25 amp and it's twice as long and twice as wide, and was pain to solder on the board. Put 4 ohm 9.5 amp current limiter which is same physical size as the original. The diode seemed fine with the multimeter test, but I replaced it just to be sure. I checked the mosfet after watching some videos on Youtube. It seemed fine apart from one test which on the video he was getting 0.002 volts but I was getting 0.2 volts so that too got thrown in the bin. So not the best of experiences but I did learn some things.
     
  10. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Nice Work! Bravo to you for a safe and successful fix!
     
  11. Bohn1

    New Member

    Nov 2, 2016
    5
    1
    did you find a replacement for the obsolete f10u60dn ?
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    Shouldn't be too hard Ultra fast 600v 10amp dual with common cathode?
    Max.
     
  13. Bohn1

    New Member

    Nov 2, 2016
    5
    1
    Thanks maxheadro,
    Being a amateur, I was hoping for a semiconductor number. However, I appreciate your info and will try to muddle through.
     
  14. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Yes I did by doing what Max suggests above. I got it from Farnell/Element14.

    FFAF60UA60DN
    Dual rectifier diode, 600V, 60A, TO3PF
     
  15. Bohn1

    New Member

    Nov 2, 2016
    5
    1
    Thanks Zariq.
    Just as an aside, this board is in my Smooth Fitness5.4 treadmill. Paid over $ 800.00. For that price I assumed I could find a schematic for the machine. Oh....how wrong I was.
    I'm hoping I can repair by 'flying blind'. Otherwise the treadmill gets thrown out. Lesson learned: Don't buy Smooth Fitnees.
    R/
    Franz
     
  16. zariq

    Thread Starter New Member

    Apr 3, 2016
    13
    1
    Don't throw it out. Since you have registered, you might as well give the board a try first.
    You wont find many schematics online, and as I found out, the companies are reluctant to provide them.

    If you are thinking of ordering the diode I mentioned previously, be warned that it is twice as tall and
    twice as wide as the original. Because the legs are further apart, they have to be bent inwards to fit the
    board. You might be able to find a smaller one for lower current.
     
  17. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Hi All, this needs to be a 30A Ultra-Fast, not dual cathode, a 10A device will RIP instantly....I will edit this post in a few minutes with a drop in replacement.....
    The first device that torched was a thermistor, which is taken OUT of the circuit after the motor rail pre-charge time, so in order for it to Blow apart, there needs to be a directly shorted motor rail....do NOT re-energize until replacing the FET, Diode, check bridge mounted to metal frame, and be sure to isolate any mounted parts from that frame of metal which gets screwed to treadmill frame ground, or an AC-Hot source to a DC circuit, and all h#ll breaks loose electrically ;o) back in a sec....
    Here is a datasheet for an engineering change (ECO) for this board say back in 2009, upgrading the original 15A to the 30A device...
    http://www.digikey.com/product-deta...onductor/FFPF30U60STU/FFPF30U60STU-ND/1055012
     
    Last edited: Nov 2, 2016
  18. Bohn1

    New Member

    Nov 2, 2016
    5
    1
    Thanks Zariq, good advice!
    I will replace all the semiconductors and hope for the best. They are affordable so no big deal.
    What would be a lower acceptable current level for that diode?
    I know my console is ok, but again, a schematic would make life so much simpler.
    Your & Maxheadroom suggestions are so welcome....
     
  19. IamJatinah

    Member

    Oct 22, 2014
    70
    14
    Hi Everyone... I found the replacement we currently use, but this now requires that we add a thermal/Mica/Isolation "pad" to the rear of this part, AND an isolating mounting washer, You must the check the mounting after you have things in place to assure you are NOT shorted to this metal frame at any point on that 2-Lead To-220ac Ultra-Fast HiperFRED "kickback" diode. This part is a critical link!
    http://www.digikey.com/product-detail/en/ixys/DSEP29-06A/DSEP29-06A-ND/1651340
    The main drive HexFet should be an IRFP260p at the least, and we are currently using a 75A Ultra-fast switch for the few cents more than the IRFP260n or IRFP260p.
    If either of these parts are shorted, you should beware of that small stand-up daughter board at the end of the circuit board! This "Daughter Board" you didn't see mentioned in these posts, but that is where the PWM generation takes place, along with some feedback and isolation paths from the "HOT" grounded side of the motor rail to the dc control power and circuits that interface with the console and the on-board control power/watchdogs. "IF" the reverse-current travels from a destroyed HexFET, at the time of melt-down of that Die, huge potentials can literally melt-over opened bond wires, sending +165vdc into the push-pull surface-mount NPN/PNP pair that provide the drive signal shaping for the IRFP260...... These little SMT transistors can blow, and they could be covered in a black potting material that you cannot get off. If you try to remove this type of potting with force, you will pull SMT parts off of their pads, pull traces, and kill that Daughter Board. You will most likely not be able to rework blown SMT transistors on this board either.....

    There is one way to see if the board is providing the 20khz or so main motor drive switching frequency to the HexFet, and that requires an oscilloscope, an isolation transformer for that said oscilloscope to plug into, probes and a tech with knowledge of "hot" grounded motor drives, inverters, converters, phasing, "Isolated Grounds", no-ground crossing and other rules to catch the pulses, and they will only appear for about 5-seconds, with the HexFet removed from the circuit, the isolated o-scope probe ground to the "hot" motor rail ground, and probe the "Gate" hole with the probe. The console would need to be connected, which also provides an "Enable" logic signal to this board for motor drive, and without the HexFet, there will be no motor movement when you press "Start" with things powered and wired up, and watch the o-Scope for the couple-second 20khz, at about +15v to the Gate of the HexFet, when the feedback pin will see no motor turning and shut off the PWM signal, leaving no signals. If you see no 20khz switching gate drive at this point after all this work, that usually means you will see a "High" level of near +15vdc to that HexFet instead of a sliced/switched frequency, and destroy itself again.
    We could go deeper as to what and how this Push/Pull surface mount pre-driver circuit works but that is getting frustratingly deep for beginners.
    Let me know if you'd like me to take a look at it or I may have one around to save a treadmill from the grave? ;o)
     
    Last edited: Nov 2, 2016
  20. Bohn1

    New Member

    Nov 2, 2016
    5
    1
    Wow
    Wow Jatinah, I am overwhelmed by your generous discussion, and will not pretend to comprehend it all. My inclination is to replace the semiconductors, one for one, and hope for the best.
    I will digest your input for possible incorporation,
    It is somewhat intimidating with ample opportunity for things to go wrong.
    Thanks to all, I am very grateful !
     
    IamJatinah likes this.
Loading...