Help Troubleshooting an Electric Scooter

Discussion in 'The Projects Forum' started by joshzstuff, Apr 24, 2012.

  1. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    My Dad had his well used Scooter (Circa early 90's) suddenly stall on him.
    He is disabled and uses it to get around, so if there is anything you know that will help my trouble shoot it it would be greatly appreciated.

    He tells me that after unloading it and briefly moving it he got on and after a 2 second acceleration, something gave out and the front drive wheel would only barely turn when it was raised off the ground (the motor had no torque)

    What I've tried so far:
    Batteries and Motor:
    When directly connecting the battery voltage to the motor it confirms that both the batteries and motor work
    [both batteries read good voltage (~12.4v) ]
    [The batteries are connected in series to power the 24v motor. ]

    This leads me to believe that there is a problem in the PCB or Drive control

    Speed Pot:
    I shorted the Speed control pot and looked for a dead spot, neither diagnostic worked so I'm forced to go to the PCB for the problem.

    The voltage reading from the scooter seems to be from 1.2volts to ~17volts from low to high speed pot setting, (or if I short the POT)

    The PCB:

    High Res pic available: Here

    This board has 3 relays:
    1 for ON/OFF
    1 for Forward
    1 for Reverse

    Since both forward and reverse exhibit the same lack of torque motor problem, I do not believe the problem to be a relay.

    I can provide more info and pictures if needed, but I don't really know where to start with the PCB trouble shooting.

    Thank you for any advice you may have.
  2. wayneh


    Sep 9, 2010
    Can you clarify what you mean by that? Did you actually measure those values, and where?

    A schematic would obviously be very helpful. Have you tried to find one? Maybe call the company?
  3. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Hello wayneh,
    I measured those values in from the point of the motor connection as the scooter was trying to turn the drive motor.

    There is a potentiometer that varies the speed of the scooter (pic below)

    If you look at the red harness in the original post, the two black wires go to this speed control.
    I shorted the pot during my testing to see if it was the cause of the problem, it was not.

    My manual has no schematics, the company is Ortho-Kinetics the brand is "Sierra" Model 441
    The search for the manufacturer lead me to this site:

    If they call me back with any schematic details I will post it here.
  4. wayneh


    Sep 9, 2010
    I'm still hung up on trying to understand that point. Is the motor seeing these voltages and not responding with a speed change? Or are these the voltages on the motor supply wires, but with the wires not connected to the motor terminal, ie. no load?

    Either way, I'm no expert on motor controllers, so we'll need other expertise here. I'm just trying to help such a person better understand your situation and findings.
  5. shortbus

    AAC Fanatic!

    Sep 30, 2009
    Have you checked the condition of the motor brushes? And the motor commutator? This is always the first place to look with motors in service for this long, around 15 to 20 years is a long time for brushes to last on something running a lot.
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
    Depending on the reversing scheme, motor current could be flowing through both relays in both directions.
  7. K7GUH


    Jan 28, 2011
    I have a similar scooter of different brand name. Called up one of the dealers advertised on the 'net, they weren't interested in giving me any info on repairing the scooter, wanted only to sell me a new one. Will have to fall back on my own resources, eh?
  8. debe

    AAC Fanatic!

    Sep 21, 2010
    Having had to repair a scooter recently with int speed control. I would be checking for poor/dry solder joints on the relays & the speed control Mosfets on the PCB. Especialy when the unit is old.

    AAC Fanatic!

    Jul 1, 2008
    Have you performed a rap tap test on it?
  10. wayneh


    Sep 9, 2010
    I prefer rock and blues. :D
    shortbus likes this.
  11. #12


    Nov 30, 2010
    I repaired one of these...once. It was corrosion in a connector from the control panel to the brain board. It got crusty because it was routed under the scooter and got water in it.

    That's my 2 cents worth.
  12. joshzstuff

    Thread Starter Member

    Sep 22, 2010
    Direct power from the Batteries to the Motor proves that the problem lies in the PCB somewhere (see "Batteries and Motor" in original post)

    No we won't! :)

    There was a great guy at the new company who returned my call and sent me a schematic, see below:


    High Res photo Available Here

    I'm going to look more closely at the connectors and the solder joints, a reflow of some of the components would be a quick fix indeed!

    Keep in mind that the nature of the failure was immediate (vs. gradually slowing down)
    Although some voltage and an undetermined amount of current is passing to the motor

    (enough to make it lightly 'buzz' and turn ever so slightly)

    I've done a fair bit of jostling with the effected components to un-case them and have plugged and unplugged the connectors to the motor and battery several times so far.
    Although I have not applied the direct 'rap' to the relays.

    Thanks everyone for your suggestions!
  13. myroona

    New Member

    Mar 28, 2012
    I had the same issue with my scooter bought back in '90s. Desoite i struugle so much to repair it, i was not able to do it. Indeed i'm not too good at mechanical works, and maybe this is the reason i was not able to do it. Whereas after reading this thread here it seems quite simple...:confused:
  14. MrChips


    Oct 2, 2009
    Wow! A schematic. Now see if that great guy at the new company will send a schematic of the PCB.
  15. MrChips


    Oct 2, 2009
    There are two motors shown in the schematic. Do you know what L and D stand for?
    Are these standard DC motors which can run by connecting it to the battery?

    Edit: I see it now - Lift and Drive. What does Lift do?