Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediately.

smhoff2019

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Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediately.

Hi All, My 10 yr old and I just took apart the control box of our CM 1936, Black and Decker cordless 36V. We were trying to figure out why the "kill bar" isn't working. Usually you have to push an orange button and pull down the "kill bar"/lever to start this mower. We just changed out the battery, and when we did, this new issue happened. You put in the key and the mower starts up immediately. No more orange push button, no more hand lever needed. To stop the mower you have to take the key out. The "kill bar", or hand lever, no longer works. So we took the control box apart and adjusted the springs attached to the hand lever and orange push button. Looked at the wires, couldn't see any obvious issue. The mower's about 4 yrs old, been pretty much problem free. Once it had an issue that, apparently, riding in our car fixed (jiggling it?). My son was mowing when the last battery died -- not sure why it died after just a year (the seller replaced it gratis). I wonder if he hit a rock and blew a circuit. There's something that my kid thinks looks like a relay in the wire box. Maybe it blew when the battery died. Also, just after the battery died, my son shook the mower around some, (though he's 10 and not that big/strong), thinking that might be the issue (like what happened when the jiggling of a car ride seemed to fix a problem). I wonder if he shook something loose this time. Anyone have any ideas? I'll post a picture next time we open the control box. Thanks very much in advance.:biggrin:
 

MowerMike

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

When you insert the key, you are enabling the start switch by closing the circuit from the battery. The start switch on the handle is closed when you press the start button and then pull the bail bar back. When you release the bail bar, the start switch is supposed to open, shutting the mower motor off. If, however, the switch is faulty and does not open as it should, then the motor will continue to run until you open the circuit by removing the key. Either the switch is stuck closed or the contacts have fused together due to a short circuit. Disconnect the battery ground cable, then check the switch wire connecting points with an ohmmeter. If the ohmmeter reads zero Ohms, then the switch is closed in which case it is faulty and needs to be replaced.
 

smhoff2019

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

When you insert the key, you are enabling the start switch by closing the circuit from the battery. The start switch on the handle is closed when you press the start button and then pull the bail bar back. When you release the bail bar, the start switch is supposed to open, shutting the mower motor off. If, however, the switch is faulty and does not open as it should, then the motor will continue to run until you open the circuit by removing the key. Either the switch is stuck closed or the contacts have fused together due to a short circuit. Disconnect the battery ground cable, then check the switch wire connecting points with an ohmmeter. If the ohmmeter reads zero Ohms, then the switch is closed in which case it is faulty and needs to be replaced.
Thank you, Mike, that is very helpful. It raises a couple more questions. I wonder what the "start switch" looks like on this mower. I'm going to take a photo of the inside of the control box if you've never seen it, and maybe you can help us figure out what/where the "start switch" is. When you open the control box on the mower a thick metal spring falls out. My kid figured out how to get it all back together. I think we did it right, but not sure. At least it fits right and the mower still works, even if the switch doesn't work right. The thick spring looks to be controlled by the bail bar. It may contact a plastic piece that is attached to a flimsier spring that is attached to the orange button. So you push the start button and spring in, maybe the black plastic piece turns when you do that. When the black plastic piece turns (if I"m right), and the bail bar is depressed, somehow (like you say), the circuit is completed. If everything's working right. It looks like the bail bar moves the thicker spring, and... presto. Somehow. Yet I don't remember seeing any wires attached to the bail bar or in that area -- not sure yet exactly how the bail bar completes the circuit. We might take a video of what happens and post it on YouTube. Would be helpful for others with the same mower. Something tells me we're not the only ones who've ever had this issue. One more thing : I forgot my high school physics -- if the switch is closed, there is current running through the wires, and so the ohmmeter will read 0 ohms, or no resistance? And, if the switch is open, and there's no current, the ohmmeter will pick that up and have a reading of resistance? We'll have to figure out where the switch wire connecting points are... Thank you again. You've taken us further. I'll look for an exploded diagram of the insides, but I don't think Black and Decker has a repair manual for this unit. Probably a lot of electric mowers have no repair manual or instructions, etc.:wink:
 

MowerMike

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Here is a link to the parts list for your mower.

https://www.ereplacementparts.com/black-and-decker-cm1936-type-36v-19in-mower-parts-c-4167_9514_173260.html

I don't know if you have a CM1936 Type 1 or Type 2 (shown), but they should be pretty much the same. The electrical switch I am referring to is part number 2 in the diagram, and there should be three wires connected to it. It is most likely the part that your son thought was a relay. The single red wire probably goes to the positive terminal on your battery, and the two other wires with a single connector probably go to the motor. One of the motor wires should be black, and that wire goes to ground. The other wire will be either red or white, and it is the hot wire to the motor. To test the switch you must first disconnect the battery negative (black) ground cable to prevent an accidental short circuit or startup. Next, disconnect the wires from the switch, set your meter to read resistance in Ohms, touch one meter probe to the switch terminal that was connected to the single red battery wire, and the other to the switch terminal that was connected to the red or white motor wire. The meter should read OL (overload), indicating infinite resistance, because the switch should be open. If the meter reads zero Ohms, it means that the switch is closed, and the switch is faulty requiring replacement. If the meter reads OL as it should, then your problem lies elsewhere.

As a clarification, resistance is measured in Ohms and current is measured in Amps. The resistance across the contacts of a closed switch will be zero regardless of whether or not there is any current flowing in the circuit. The bail bar and button are part of a safety startup mechanism, that prevents accidental startup if either is moved individually. When depressed and held, the button pushes the bail bar into a mechanism that actuates the switch when the bail bar is pulled back. Once the bail bar is pulled back, the button can be released. When the bail bar is released, the mower is supposed to shut off, preventing the operator from walking away from the mower while it is still operating.
 
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smhoff2019

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Here is a link to the parts list for your mower.

https://www.ereplacementparts.com/black-and-decker-cm1936-type-36v-19in-mower-parts-c-4167_9514_173260.html

I don't know if you have a CM1936 Type 1 or Type 2 (shown), but they should be pretty much the same. The electrical switch I am referring to is part number 2 in the diagram, and there should be three wires connected to it. It is most likely the part that your son thought was a relay. The single red wire probably goes to the positive terminal on your battery, and the two other wires with a single connector probably go to the motor. One of the motor wires should be black, and that wire goes to ground. The other wire will be either red or white, and it is the hot wire to the motor. To test the switch you must first disconnect the battery negative (black) ground cable to prevent an accidental short circuit or startup. Next, disconnect the wires from the switch, set your meter to read resistance in Ohms, touch one meter probe to the switch terminal that was connected to the single red battery wire, and the other to the switch terminal that was connected to the red or white motor wire. The meter should read OL (overload), indicating infinite resistance, because the switch should be open. If the meter reads zero Ohms, it means that the switch is closed, and the switch is faulty requiring replacement. If the meter reads OL as it should, then your problem lies elsewhere.

As a clarification, resistance is measured in Ohms and current is measured in Amps. The resistance across the contacts of a closed switch will be zero regardless of whether or not there is any current flowing in the circuit. The bail bar and button are part of a safety startup mechanism, that prevents accidental startup if either is moved individually. When depressed and held, the button pushes the bail bar into a mechanism that actuates the switch when the bail bar is pulled back. Once the bail bar is pulled back, the button can be released. When the bail bar is released, the mower is supposed to shut off, preventing the operator from walking away from the mower while it is still operating.
Thank you very much, Mike! This gives us vital info. Like "what is the switch". And how to test the switch. If the switch is good, it's going to need more sleuthing, but we'll cross that bridge. Come next weekend we're going to give it a whirl. Really appreciate your help. By the way, my son was wondering if the way it's working now hurts the battery/mower at all -- it's like you're completing the circuit when it's at full speed. But that reminds me of the way I've seen a Tesla go from 0 to 60, or the way this lawn mower, even, goes from 0 to "full throttle" fast.

Also, we were wondering if there's a way to know exactly how the torsion spring (part 23) and crank (part 7) are oriented when you put it back together. I think we got them back in the right position, but I'm not 100% sure, and I wonder if this could be the issue. If jiggling shook something loose, then maybe. Sounds like maybe it's not the issue.
 

MowerMike

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Thank you very much, Mike! This gives us vital info. Like "what is the switch". And how to test the switch. If the switch is good, it's going to need more sleuthing, but we'll cross that bridge. Come next weekend we're going to give it a whirl. Really appreciate your help. By the way, my son was wondering if the way it's working now hurts the battery/mower at all -- it's like you're completing the circuit when it's at full speed. But that reminds me of the way I've seen a Tesla go from 0 to 60, or the way this lawn mower, even, goes from 0 to "full throttle" fast.

Also, we were wondering if there's a way to know exactly how the torsion spring (part 23) and crank (part 7) are oriented when you put it back together. I think we got them back in the right position, but I'm not 100% sure, and I wonder if this could be the issue. If jiggling shook something loose, then maybe. Sounds like maybe it's not the issue.
I don’t think that using this mower by starting it directly with the key will damage the battery or motor, however, you may damage/burn to key contacts by doing so. More importantly, you should NOT attempt to charge the battery while the motor is live, and should wait until this problem is fixed. As to the possibility that you somehow reassembled the switch box incorrectly, I think this is unlikely, since the problem occurred before you opened it up.
 

smhoff2019

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Thank you again. Unfortunately, I already did charge the battery. Just went out and unplugged it, when I read your message. (As you know, the mfr. recommends leaving it plugged in [when everything is working normally]). Now I'm wondering if (a) the battery will be OK after having been left plugged in for a couple days; (b) what exactly the problem is with plugging it in to charge while the motor is live; (c) whether a problem with the switch or a short circuit caused the battery to drain before it should have. The mower/battery died, at first, while my son was mowing. It just suddenly died. At that moment, the bail bar was working properly. I guess that's a clue. I've got to think about this. But I'm glad you're recommending fixing the switch/short issue before we go on.
 

MowerMike

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Thank you again. Unfortunately, I already did charge the battery. Just went out and unplugged it, when I read your message. (As you know, the mfr. recommends leaving it plugged in [when everything is working normally]). Now I'm wondering if (a) the battery will be OK after having been left plugged in for a couple days; (b) what exactly the problem is with plugging it in to charge while the motor is live; (c) whether a problem with the switch or a short circuit caused the battery to drain before it should have. The mower/battery died, at first, while my son was mowing. It just suddenly died. At that moment, the bail bar was working properly. I guess that's a clue. I've got to think about this. But I'm glad you're recommending fixing the switch/short issue before we go on.
The reason I said not to charge the battery with the motor switch closed is that the charger for your mower plugs into the same circuit that the key uses to enable the motor circuit. Depending on how the mower is wired, this could possibly damage the charger. You might want check the battery with a voltmeter to see if it actually was being charged.
 

smhoff2019

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

The reason I said not to charge the battery with the motor switch closed is that the charger for your mower plugs into the same circuit that the key uses to enable the motor circuit. Depending on how the mower is wired, this could possibly damage the charger. You might want check the battery with a voltmeter to see if it actually was being charged.
Thank you again. We'll be working on this over the weekend. Really appreciate your insights.:smile:
 

smhoff2019

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Re: Black & Decker CM 1936 -- "kill bar" doesn't work. Put key in starts up immediat

Hi Mike, Wanted to update you. We finally got a chance to take the thing apart again. Should have taken a photo of how my kid fit the springs back together. Can do that later if needed. Anyway, this is what the situation was. I have to admit my 10 yr old kid is better at figuring out how it all fits together than I am. I took a photo of the switch. It should be attached to this. As you predicted, there was a red wire, a white wire, and a black wire connected to the switch. The white wire was in the lower left corner. The black wire was in the upper right corner. The red wire was in the lower right corner. When we held our multimeter probes (reading ohms) to the red and white wires' connection points, we got basically no reading, it seemed -- it was a reading of constant one with no movement. When we held the probes to the red and black connector areas, we got a reading like between 1.2 and 2.1 or so. We never got OL. We had the multimeter on the lowest range, like 20. My kid also noticed that the metal connection piece that is screwed on across the front of the switch looks like it might be "split" or "broken". It is pictured in the attached JPEG. Does that seem normal? If so, going by your previous post, it seems our problem might NOT be the switch. But I'll let you judge, based on the above. Also, like I said, I'm not sure we have the bigger, more rigid spring (torsion spring?) on 100% correct. Maybe that is an issue. Awaiting your insight. Thanks a million.
 

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