Troubleshooting shorted throttle controller

I'm attempting to troubleshoot a shorted throttle controller cable. The throttle unit was severed and I believe one of the data lines was shorted to +. The bike is a Wave 1.0, the controller is marked KT-LCD800 link: http://www.szktdz.com/upload/file/20140724/20140724012355_80760.pdf

Amazon link:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.amazon.com/Electric-Bicycle-Control-Display-Controller/dp/B07MH1LGP8&ved=2ahUKEwjI89bx_93jAhUPnOAKHSReAnEQFjAAegQIARAB&usg=AOvVaw0qpRLAbdld6JHs35HfLGjT

I'm seeing no voltage on the lines to the throttle and I think it was shorted. Are the 2 data lines typically protected?

I have a hot air rework soldering station and I'm comfortable w SMD soldering but I just don't know much about motor controllers. Anyone know where I should start looking or if it's worth the trouble or have any insight?

When repairing cables, the general MO is to unplug the cable, carfully remove insulation as needed, slip shrink tube over the wire to be repaired, (it can not be heated while soldering or it will shrink in the wrong spot), solder the wires together, slide the shrink tubing over the solder repair and heat until it shrinks-to-fit.

My suggestion is this: Take some pictures of the damage so we can see what you are doing. Make sure they are in focus and under 512k per picture so you can post them on ES.

It will be easier for us to talk you through it if we can see what yo are doing.

That's not the throttle you linked, it's a display.
So I not sure which you are asking about. I'm guessing you are talking about the display and if you are trying to find the pos. and neg. feeds, I don't know what to tell you. Pretty sure both the display and the controller need to be hooked up before they power-up.
The wires aren't color coded?

NStone775 said:

I'm attempting to troubleshoot a shorted throttle controller cable. The throttle unit was severed and I believe one of the data lines was shorted to +. The bike is a Wave 1.0, the controller is marked KT-LCD800 link: http://www.szktdz.com/upload/file/20140724/20140724012355_80760.pdf

Amazon link:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.amazon.com/Electric-Bicycle-Control-Display-Controller/dp/B07MH1LGP8&ved=2ahUKEwjI89bx_93jAhUPnOAKHSReAnEQFjAAegQIARAB&usg=AOvVaw0qpRLAbdld6JHs35HfLGjT

I'm seeing no voltage on the lines to the throttle and I think it was shorted. Are the 2 data lines typically protected?

I have a hot air rework soldering station and I'm comfortable w SMD soldering but I just don't know much about motor controllers. Anyone know where I should start looking or if it's worth the trouble or have any insight?

Click to expand...

Just to ensure we're using the same nomenclature, looking at pictures of your bike online, the controller is located behind the seat tube, the display is located near the left grip of the handlebar, and per the specs, it looks like the throttle is located near the right grip. Given that, was it the throttle or display that was damaged?

So I'm referring to the display mounted on the handlebars not the motor controller.
The 5 conductor wire was severed right at the display box & I believe the data line(s) were shorted to the +V.
I fixed the severed wire using a 5pin JST connector & some cat5 cable soldered to the board of the display. I'm certain the lines are wired correct but I'm seeing no voltage on the lines coming from the motor controller to the display box and the bike will not respond power on & the display shows no signs of life. Battery had 52v going into the motor controller & the fuse was good, but I don't know where to go from here & if it's worth trying to open the controller & trouble shoot. Could shorting the wires running to the display blow the whole controller? I'd imagine it's only running something like 5v to the display box but not 100% sure. Here are some pics,







Just to be clear, I believe I have the severed wire issue is fixed (well enough) but there appears to be something else wrong.

Is it possible to test the display or controller in isolation?

It may not be worth it to try and troubleshoot it.

Was it you, or someone else who cut all the wires at once?

So it boils down to what do you do now?
How much is your time worth to you?

See if the bike works without the display, and use a new throttle.

Thanks for clarifying. Looking at the manual for the display, you have full battery voltage going in, not 5V (makes sense since the display shows the charge level), so yes, there is a possibility of frying both the display and controller.

Depending on your controller, you may be able to turn it on without the display if you can locate the wire to apply battery voltage to (one of the wires the display is attached to), and use the throttle to see if the controller is fried or just the display.


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Generally the wires from a controller to it's display include a ground, battery positive, battery return (ignition, keyswitch, etc), serial out, and serial in.

If there is no battery voltage on any of the wires coming from the controller, with only battery connected to the controller, then you'd have to check inside tthe controller to be sure it actually has battery voltage reaching it.

If it does, then something inside the controller has failed open, but there should only be wires or traces on the board between the battery positive into the controller, and battery positive out to the display. You can use the ohms setting on your multimeter, with battery disconnected from controller, to measure between battery positive output wire and battery positive input, to verify continuity.

Same thing for ground.


If there is battery positive out, but no return from the display, check the display for battery voltage inside it. If it doesn't have any, the connection is broken to the controller.

If there is battery positive inside the display, but the display will not power on, then the display is dead, most likley killed by battery power being shorted to serial data lines and going directly into the MCU. That would also probably kill the controlelr MCU at teh same moment.

You can test for this by shorting the battery positive output on the controller to the battery positive return from the LCD. The controller will turn on and then respond probably at it's default power-on levels.

It is very easy to fry the controller’s 5v circuit, then the controller doesn’t respond to e-brakes, throttle, hall sensors, and any other accessory that is on the control circuit. So it is easy to diagnose too. Some controllers require a display unit that serves as control interface, some you can program with a computer or cell phone, some are preset at factory and can’t be set. As mentioned previously, some controllers are very cheap, thus not worth the time and trouble to fix.

Wow thanks for all the excellent responses. I've never ridden the bike, this repair is pro-bono work for an older guy on fixed income and it's his only mode of transportation. So I'm working on almost zero budget.... And quickly getting in over my head. But this gives me a couple of directions to go.

The motor controller passing full voltage to the display does make sense. I'm presuming the b in Vb+ as seen in the display manual refers to the battery, as in full battery voltage. It sounds like I may be able to supply it w Vb+ & ground directly off the battery which, if the display is working, might show the battery level.

Also didn't realize the throttle is totally separate. As mentioned, if I can supply whatever signal the display sends back to the controller I might be able to get it to turn on. Now the thing I'm unsure about it's how does the display tell the controller to turn on? If it's a digital signal over the serial lines it's probably hopeless. But if it's just a matter of sending vb+ down the line marked "control" in the manual, that's easy enough to try. The manual shows 5 lines going to the display marked vb+, control, gnd, data1, & data2. Anyone have any experience w how that control line is used? My gut feeling is it's just gnd=off & high=on, but I may be way off. And is there any way to check that w out just trying it, like maybe checking the resistance between control & gnd (I'm presuming it'd be pulled low when nothing is connected)?

NStone775 said:

Now the thing I'm unsure about it's how does the display tell the controller to turn on? If it's a digital signal over the serial lines it's probably hopeless. But if it's just a matter of sending vb+ down the line marked "control" in the manual, that's easy enough to try. The manual shows 5 lines going to the display marked vb+, control, gnd, data1, & data2. Anyone have any experience w how that control line is used? My gut feeling is it's just gnd=off & high=on, but I may be way off.

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Almost certainly the "control" line is just the "keyswitch / ignition" line, which returns battery voltage to the controller to give it power into it's low-voltage-power-supply (LVPS) that supplies 5v and 12v to all the brain bits inside. (MCU, gate drivers, etc).

Just short Vb+ to Control, with the display left disconnected completely, and the controller will turn on if it's not destroyed. It will only operate in basic power-on mode without the display to tell it to change levels, etc., but it'll do whatever it would normally do when first powered up.

If you get smoke out of the controller, then either something in it was already fried by the original problem (which is pretty likely anyway), or Control is not the battery positive return line. (but I don't see another one it could be).

And is there any way to check that w out just trying it, like maybe checking the resistance between control & gnd (I'm presuming it'd be pulled low when nothing is connected)?

Click to expand...

Not really. You'd have to open the controlelr to see where it goes. Almost certainly, it goes to the input side of the LVPS (often a big power resistor on the input pin of an LM317, but sometimes they use an SMPS for the LVPS).




Realistically you're probably going to have to replace the controller *and* display with new set that do the same job (but make sure you get them as a matched kit, as the display or controller from a different brand or model isn't likely to work without it's counterpart).

When repairing the cable, you obviously matched the wire colors. SInce you supplied the PDF, this is the likely definitions,

Red VB: battery voltage, Has to be battery voltage if display can show battery status.
Blue Control: The 880 probably connects blue to red to start controller.
GND Black: battery and system ground
Data1 Green: serial data
Data2 Yellow: serial data

You should measure battery voltage between VB and GND. The 880 will generate its own onboard voltage from VB. Often, a controller can be run w/o these displays by jumpering VB to Control, and DATA1 to DATA2.

If you don't have power between VB and GND. I think amber is correct. Controller could be toasted if you have battery power going into it.