Bafang display not turning on

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Sketch89   10 µW

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Bafang display not turning on

Post by Sketch89 » Jun 19 2022 9:50am

Recently we bought an electric Vogue 2 carry bike. The bike has a Bafang m400 motor and i believe an Bafang C7 display. We used the bike a couple of times and was really nice. However, after using it last wednesday without any problem we noticed the diplay didn't start today. The battery is fully charged. We cant seem to turn on the display again. I checked most wires and everything looks fine. Disconnected and connected the battery again as wel as disconnecting and connecting the cable of the display.
Hope you guys can help me to troubleshoot.

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fechter   100 GW

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Re: Bafang display not turning on

Post by fechter » Jun 19 2022 10:18am

The power goes from the battery through the controller, then to the display and back to the controller when turned on. You did what I would try first, unplug all connections, inspect the pins and plug them back in.

If a wire breaks inside a cable somewhere, it can be challenging to troubleshoot because the connectors are shrouded and you can't probe them with a meter easily.

If you have a voltmeter, you want to check the battery voltage going to the motor first. One common failure is the battery BMS detects a fault and cuts off the output.

If the battery voltage is OK, then you want to see if the voltage is getting to the display but there is no handy way to do this. If you unplug the display, you can use small, solid strand wire to poke into the sockets and go to your meter.
Bafang 5 pin display connector.png
Bafang 5 pin display connector.png (26.73 KiB) Viewed 224 times
Measure voltage between pin 1 and pin 3 and you should see pack voltage. Be super careful not to let the pins short to each other.
If you have pack voltage, then it would indicate a display problem. If no pack voltage, the problem is in the controller or controller cables.
"One test is worth a thousand opinions"

Sketch89   10 µW

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Re: Bafang display not turning on

Post by Sketch89 » Jun 19 2022 12:42pm

Thanks @fechter, that was real helpful! I didn't know how to measure at the battery so went straight for the green connector. I got like a really cheap aliexpress multimeter with shitty probes and it measures around 42V. I think this is good news, at least i hope, that the problem is only with the display. At least some electricity is coming through. I used below settings on the multi-meter to measure. Dont mind the value, i couldn't measure AND make a photo at the same time :wink:
20220619_193542.jpg
20220619_193542.jpg (935.57 KiB) Viewed 218 times
Maybe i should go to the bikestore and ask if I may try one of their displays. What do you think?

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fechter   100 GW

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Re: Bafang display not turning on

Post by fechter » Jun 19 2022 6:09pm

Yes, if your battery is nominal 36v, then that is a good reading.

Testing with a known good display would be a great test, but if I was a bike store I wouldn't let somebody borrow mine.
You could also try disconnecting any brake switch wires and throttle and see if the display will come on.
Another test I've seen people try is to place a small jumper wire from pin 3 to pin 5 and see if the motor will run.
"One test is worth a thousand opinions"

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E-HP   1.21 GW

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Re: Bafang display not turning on

Post by E-HP » Jun 19 2022 9:53pm

Sketch89 wrote:
Jun 19 2022 9:50am
However, after using it last wednesday without any problem we noticed the diplay didn't start today. The battery is fully charged.
Is the bike working otherwise, or is nothing turning on?

Sketch89   10 µW

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Re: Bafang display not turning on

Post by Sketch89 » Jun 21 2022 4:03am

It was indeed the display that just stopped working al lof a sudden. New display and it works again.

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fechter   100 GW

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Re: Bafang display not turning on

Post by fechter » Jun 21 2022 9:35am

Thanks for reporting back.

Unfortunately, the displays are pretty hard to take apart without breaking them since they are all sealed.
But since you have a bad one, there isn't much to lose by attempting to take it apart. If you take it apart, you can test the cable from the plug to where the wires attach to the display board and see if any of the wires are broken. Sometimes there could just be a bad solder connection that can be fixed. If the wires broke inside the cable, you can buy a display extension cable and cut one end off to make a replacement cable.
"One test is worth a thousand opinions"

Sketch89   10 µW

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Re: Bafang display not turning on

Post by Sketch89 » Jun 22 2022 1:53pm

fechter wrote:
Jun 21 2022 9:35am
Thanks for reporting back.

Unfortunately, the displays are pretty hard to take apart without breaking them since they are all sealed.
But since you have a bad one, there isn't much to lose by attempting to take it apart. If you take it apart, you can test the cable from the plug to where the wires attach to the display board and see if any of the wires are broken. Sometimes there could just be a bad solder connection that can be fixed. If the wires broke inside the cable, you can buy a display extension cable and cut one end off to make a replacement cable.
That would be a good test indeed, maybe i will have a spare. As it was pretty expensive (175 Euro). Not sure how to test the cables though. I already managed to open the display to see how it was done.

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fechter   100 GW

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Re: Bafang display not turning on

Post by fechter » Jun 22 2022 6:42pm

I would just check continuity from the cable connector to the end of each wire inside the display just to make sure none of the wires are broken inside the cable (measure ohms). If the continuity checks out OK, then the problem is on the display board.
"One test is worth a thousand opinions"

Sketch89   10 µW

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Re: Bafang display not turning on

Post by Sketch89 » Jun 23 2022 2:53am

Can i do that with the same multimeter? sorry, bit of a noob here.

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fechter   100 GW

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Re: Bafang display not turning on

Post by fechter » Jun 23 2022 9:25am

Most multimeters have an ohms or continuity function. In this mode, touch the meter probes together and you should see the ohms drop to near zero. Then you put one probe on a connector pin and the other probe on the wire where it attaches to the display board and see if the meter reads near zero. Do this for all wires. If any of the wires are broken, the meter will not change. It's probably sort of a long shot that a wire broke unless the cable was damaged.
"One test is worth a thousand opinions"

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