Dremel 400 Digital - Reassembly - Where does this black wire connect? - Page 1
Forum section: electronics / repair

author: ukrepair
author_rank: Newbie
timestamp: September 20, 2016, 10:33:51 pm
content: Hello EEVers,I took apart this Dremel 400 Digital to repair for a friend but I can't figure out where this black wire and contact slide in/connect. It just sort of popped out when I split the case open.I thought it might be a Ground wire to the case, but the case is plastic...The wire in question is the loose black wire in the attached picture.Has anyone disassembled one of these previously and could direct me?Everything is cleaned and ready to go, just this damned wire got me stumped!Thanks for looking!

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 10:56:12 pm
content: Cant give you a direct answer but does the black wire connect to earth in your mains plug? If so, its obviously an earth and probably does clamp to either the casing or the motor assembly. The casing could well be EMC shielded plastic that conducts. You could check the inside of the body with a meter for Kohms/Mohms continuity.

author: helius
author_rank: Super Contributor
timestamp: September 20, 2016, 11:39:11 pm
content: These are Class 2 devices, they don't have ground. The copper plate is part of the power switch.

author: voltz
author_rank: Frequent Contributor
timestamp: September 20, 2016, 11:44:34 pm
content: Class 2.

author: DimitriP
author_rank: Super Contributor
timestamp: September 21, 2016, 12:08:01 am
content: How about right there ?

author: DimitriP
author_rank: Super Contributor
timestamp: September 21, 2016, 12:22:15 am
content: After I posted I went looking at the manual and the wire ....doesn't exist! So it'll be interestinghttp://www.manualslib.com/manual/40842/Dremel-400-Series-Digital-398-49.html?page=22#manual

author: amyk
author_rank: Super Contributor
timestamp: September 21, 2016, 01:48:24 am
content: It looks like a part of a switch, but you should see what the other end connects to and figure out its function from that.http://www.homediystuff.com/wp-content/uploads/2013/09/switch_assembly_DIY_dremel_fix_rotary_drill_tool_homediystuff.jpg

author: silverlego3
author_rank: Contributor
timestamp: September 21, 2016, 10:06:49 pm
content: Quote from: helius on September 20, 2016, 11:39:11 pmI agree, it's part of the power switch.

author: ukrepair
author_rank: Newbie
timestamp: September 21, 2016, 10:57:37 pm
content: Thank you all so much for the interest and ideas!I include some extra pics to further illustrate the issue.@Voltz and Helius You are correct, only live and neutral are arriving at the PCB from the plug, no earth involved.@DimitriP That's a rubber seal surrounding a bearing and the copper contact doesn't seem to fit there or in the opposite housing - it just prevents the case from closing at all. Thanks for the idea though. The manual not showing it has me stumped too! As you can see from the pics, it does exist and is connected to the PCB near what I believe are a blue capacitor and a large white heatsink/resistor. The red brush contact wire also sources from this area.Wilfred's suggestion about being part of the brush contact assembly was my first instinct in fact but there is no visible gap in the assembly for it to slide into without permanently blocking the ports for brush ingress/egress. Also, the curvature (correctly described as larger radius than the motor) suggests something different.Silverlego3 and Amyk - What could I check with multimeter? Continuity to another part of the PCB? It seems to be associated with the capacitor and ceramic heatsink, if that gives you any clues?I'll post some more close-up pics of the brush assembly when the opportunity arises tomorrow or later if I can.Thanks again for the help. Great site you savvy fellows inhabit! I hope to contribute where I can, if I can and I certainly have a few other on-hold projects... for another day, perhaps.

author: tronde
author_rank: Frequent Contributor
timestamp: September 22, 2016, 12:00:35 am
content: Place the speed controller where it belongs in the shell together with the motor and connect the positive and negative wires to the motor. Then it can be easier to see where it is possible to connect the unknown wire. Take a few pictures from different angles.

author: helius
author_rank: Super Contributor
timestamp: September 22, 2016, 04:25:57 am
content: Well, if it doesn't fit under the power switch, there is another possibility. See here:Not the same model, but could give you some ideas.

author: Theobald
author_rank: Contributor
timestamp: September 22, 2016, 08:57:01 am
content: If the blue cap is connected to the black wire and something like 2n2Y2, it can be the EMC filter. Then connect the clip to the motor's stator.RegardsTheo

author: ukrepair
author_rank: Newbie
timestamp: September 22, 2016, 08:19:35 pm
content: I may be making some progress!Here is a pic of the assembly... but assembled in the other half of the casing. The clue should have been the fact that the power lead had to be screwed into this side of the casing when I first started. Also, the rotor locking button was fiddly to say the least during my first efforts!When the power switch and wiring is attached this other way around, the unknown black wire hangs fairly naturally toward the central part of the casing near the stator as correctly predicted by Theobald with guidance to reassemble and look again from Tronde and Helius - many thanks for the ideas!The curve still makes me wonder but having placed it there, tried it and it worked, i'm not complaining. So, EMC, some sort of noise filter (the white block ceramic?) for the circuit?Now that it is clean and reassembled, hopefully correctly, and at least trying to turn when switched on - I have another problem.So, it kind of wants to turn but needs a push to get it started and then starts sparking quite a lot inside near the brush ports.When I push harder on the brush retainers, it seems to lessen the sparking a bit but I have to turn it off after a few seconds because the smell isn't great.Before I turn it on again and break it, do you guys/gals think changing the brushes would be a wise next move or does it seem worse than I fear?There seems to be plenty of depth to the brushes but I know they have less than optimal design. What is the spec length for 398/400 brushes, I wonder?Anyway, wanted to keep you all updated as to progress.Maybe some other noob will benefit from my lack of experience with electric motors."I tried it the other way and it worked!". Not universally the best advice* at all times but on this occasion, at least, it holds true!*e.g. Specific Polarity Devices, Wives, Motorways - the blacklist is endless.If this is indeed the solution to my original problem, I can only apologise for the simplicity of the solution and the simple-mindedness of the problem's author.

author: voltz
author_rank: Frequent Contributor
timestamp: September 22, 2016, 08:59:26 pm
content: That looks convincing. The copper tag seems to fit perfectly in the plastic moulding. It also explains why the copper contact is curved to get a better contact to the motor body. If the other end is to a "blue cap" or "white block", that sounds like a capacitor or emc type filter. Makes sense.In a way, this IS an earth contact, but not used for safety in the classic sense, rather for EMC reduction.The brushes may well need replacing. Looking at the motor, those contacts look quite black, a sign of brush wear. Give those a clean too with a tooth brush and IPA. Hopefully the motor contacts are not damaged from pitting.

author: DimitriP
author_rank: Super Contributor
timestamp: September 22, 2016, 10:51:22 pm
content: Replacing the brushes will probably do the trick as well but in the meantime, sand them down juuuust a bit to take some of the curvature off. Worse case you need new brushes, best case you bought some more time.

author: Theobald
author_rank: Contributor
timestamp: September 23, 2016, 07:19:44 am
content: "If this is indeed the solution to my original problem, I can only apologise for the simplicity of the solution and the simple-mindedness of the problem's author."Connect a wire to a metallic part when you don't have a primary earth (yellow/green wire) is not obvious .... even for some EE. But you're right, safety 1st: if you don't know, don't try it on 230VAC ! Always check the insulation between conductive parts and mains after reassembling keeps you alive. A low cost multimeter will do the job.RegardsPS you can read 2n2/Y2 written on the blue capacitor on the 2 last pictures, it is the EMC 'filter', (for EE only: returns the common mode noise to the neutral wire via the X2 capacitor, EDIT: may be the white block).Theo