Help Troubleshooting an Electric Scooter

[joshzstuff]

Hello
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.

 

[Harald Kapp]

Below that "golden" heat sink there seem to be 4 MOSFETs This could be a so called H-bridge or simply a PWM control for the motor. Probably one or more of these transistors gave out. You could measure the voltaeg across Drain-Source of these transistors at different speed settings (Drain is marked "D", Source is marked "S" on the transistor case). Do you see any difference that relates to the speed setting?
The same goes for the Gate-Source Voltage.
If you hace access to an oscilloscope and can observe waveforms? The voltages on these transistors most likely are switched, so a multimeter will be of limited help.

If you see an active Gate-Source Voltage (likely positive) but no decrease in Drain-Source voltage when you increase the speed setting, the corresponding transistor is most likely defect.

I think I can see part of a Siemens Logo on one of the transistors.Can you identify the type? You will have to detach the heat sink for that. If you do, have some thermally conductive paste at hand and put a drop of that paste on each transistor before re-mounting the heat sink.

Harald