KT LCD5 turns on and then straight off

[roques]

I've had an electric bike for around a year and a half now. It's an Urban Drivestyle Uni Micro and it's been great.

I've just started having an issue with the KT-LCD5 controller however. When I go to turn the bike on (batteries all charged) I press the power on button and the display comes on. However as soon as I remove my finger it goes straight off again.

This happened last week and there seemed to be an issue with the battery connectors which is fixed now and it worked fine for a few days, but now it's just stopped working again.

I've got some relatively decent knowledge of fixing electronics so I've checked battery voltage and opened the controller up and it looks visibly fine.

Nas anyone got any ideas what could be causing this and how to fix it short of buying a new display? I'm reluctant to buy a new display because I don't know if that's the issue or if it could be the controller.

 

[Nealh]

Check for battery voltage on the wire supply to the display, if you get a good reading then the display may be faulty. One wants the Gnd & V+ wires/contacts.

 

[roques]

Check for battery voltage on the wire supply to the display, if you get a good reading then the display may be faulty. One wants the Gnd & V+ wires/contacts.

Checked those and it's showing the same voltage as the battery...

 

[Nealh]

A fault within likely then, a broken off wire from a solder pad or a broken wire in the cable ?
Or may be just a faulty button switch.

 

[roques]

A fault within likely then, a broken off wire from a solder pad or a broken wire in the cable ?
Or may be just a faulty button switch.

The solder pads are okay and the PCB looks intact and not damaged.

I'm trying to work out which wire it could be that's damaged - as clearly the power wires are okay because the display does turn on just not stay on.

I can't imagine Rx and Tx would be causing it. I can't find what the blue wire (labelled 'control' in the manual) does to work out if it could be this (or indeed where this should be attached to).

 

[Nealh]

The blue wire sends a 5v signal back to the controller so if compromised one assumes the controller shuts everything down, once the 5v is confirmed then rx /tx comm's as we know send the correct protocols for the parameters to work.
One assumes a switch/mosfet is used on the blue line.

 

[Nealh]

Are using julet or sm connector for the display ?

 

[roques]

The blue wire sends a 5v signal back to the controller so if compromised one assumes the controller shuts everything down, once the 5v is confirmed then rx /tx comm's as we know send the correct protocols for the parameters to work.
One assumes a switch/mosfet is used on the blue line.

So I've now tried the blue wire with a voltmeter and it's not got any voltage. So I'm guessing there is something wrong elsewhere.

Any ideas where to begin to look?

 

[roques]

Are using julet or sm connector for the display ?

Its a waterproof type one, not sure of the name. It's not an SM connector though

 

[Nealh]

The blue wire voltage is a return switched voltage via the display, this voltage powers the 5v rail for PAS/throttle etc.

 

[Bikes4two]

.......... I press the power on button and the display comes on. However as soon as I remove my finger it goes straight off again........

• I'm new to ebikes but not electronics and from your description above, my first thoughts are that the problem lays within the controller.
• I say this without any specific knowledge of the circuits involved here, but however it works, the power is not staying latched on when you press the on/off button.
• Assuming the latching function is electronic of some sort, the question is where is the latching circuit - in the display or the controller? I'd think most likely in the controller but that is just an intuitive guess.

Happy to be corrected

 

[Nealh]

The latching occurs in the display and is what the on of button does, the 5v line is then route back to the controller once the display sees the correct battery value in the voltage range

 

[Bikes4two]

The latching occurs in the display and is what the on of button does, the 5v line is then route back to the controller once the display sees the correct battery value in the voltage range

Ah right - every day's a school day - subsequent to my post I found the diagram below - maybe @roques you could temporarily wire up as per the pic to eliminate/determine the display as the problem?

 

[Nealh]

Yep the kt short for use without a display one won't get throttle but will get PAS 1 only for low power.
If one hasn't an end cap simply buy a julet 5 pin green with wire tails and short the desired wires together and heat shrink them, then shrink the whole lot afterwards.
Once confirmed all is working buy anew kt display, the lcd4 is a neat small solution over the LCD3 but has not watts or clock to show. Other lcd4 does have PAS levels, speed, trip, odo, back light walk assist & critically voltage readouts as well as all the P & C settings.

 

[Bikes4two]

• I'm new to ebikes but not electronics and from your description above, my first thoughts are that the problem lays within the controller.
• I say this without any specific knowledge of the circuits involved here, but however it works, the power is not staying latched on when you press the on/off button.
• Assuming the latching function is electronic of some sort, the question is where is the latching circuit - in the display or the controller? I'd think most likely in the controller but that is just an intuitive guess.

Happy to be corrected

So an update along with some diagnosis on my own 36v 250w TSDZ2 with VLCD6 display: -

• this motor is a couple of months old and has 1440Km on the clock, is ridden mostly in ECO mode with the assist speed set to 25kmh - so it's had a gentle life.
• after a few intermittent cases of the display not switching on at first attempt, I am now unable to switch on at all.
• It is fortunate that I have two bikes with identical setups and am therefore able to swap out difference components - so a WORKING ebike and a NON-WORKING ebike
• the first suspect was the VLCD6 display but the display on the non-working bike worked fine on the other bike, whilst the display from the working bike did not power up the non-working bike
• I took the front covers of both displays and could see four coloured wires soldered to a circuit board.
• Assuming that BLACK was the 0v line, I measured the voltages on each wire on both bikes and the results are tabulated below.
• The first thing to note is that full voltage (36v nominal) is fed to the display where clearly when switching on, a 5v (nominal) signal is passed back down one (or more) of the other wires (the RED and BLUE). I do not know the function of these connections - any guidance out there?
• To me these findings indicate a probable controller issue. I have emailed PSW Power, (the supplier) with my findings and received a response the next working day asking for photos of the external motor label and the one on the controller (accessible after removing a cover - just 4 screws). PSW Power have a reasonable record for customer service, but clearly they need to be careful about what end users say about their problems, but for me, so far so good.
• It might be a broken or dry joint but I'm not doing a stripdown until PSW Power tell me what their next action is - if it is indeed a controller problem, I doubt that I'm the first with this symptom and I hope therefore that they will send out a replacment. I will update this thread as necessary.
  (EDIT/UPDATE - as per today's email (21Dec21)PSW Power are sending a replacement controller )
• All contributions/comments are welcome.
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