Dremel 358-5

[peak4Participant @peak4]

Hello, Does anyone have an older Dremel Moto-Tool Model 358-5 variable speed, and who is able to have a look inside to confirm a component number please .

I do but the variable speed no longer works, just the Off/On on the pot, so it is still usable.
I just had a look inside and the only semiconductor is labelled as a voltage regulator L7805CV
My own experience of this device is as a low voltage regulator, so I don't know if it has previously been replaced with the wrong item.
I have tried swapping it for a direct number replacement, but still no vari speed.

Cheers
Bill

[peak4Participant @peak4]

[Grindstone CowboyParticipant @grindstonecowboy]

Sorry, just checked and mine is Mod 395 Type 5, but happy to have a look if it might help?

Rob

[peak4Participant @peak4]

Posted by Grindstone Cowboy on 25/11/2020 17:49:55:

Sorry, just checked and mine is Mod 395 Type 5, but happy to have a look if it might help?

Rob

Many thanks, but it looks to work a different way.
Mine has a rotary pot on the opposite end to the chuck, which incorporates a 240V off-on switch.
I've not mapped the circuit out, but some sort of voltage divider and a 3 pin IC of some kind.
I know what's fitted, (and labelled as an L7805CV) but not convinced it's correct.

Bill

[Grindstone CowboyParticipant @grindstonecowboy]

Yep, probably no use at all, but I took it apart anyway so I could brush the dust out. There is something in there marked BT134W, with three legs and a heatsink/mounting tab. Surface mounted device, Googled it and it's a triac.

Surprisingly it still works after re-assembly

Rob

Edit – Maybe in a circuit similar to this?

Edited By Grindstone Cowboy on 25/11/2020 22:09:02

[peak4Participant @peak4]

Posted by Grindstone Cowboy on 25/11/2020 21:55:28:

…………………………… Googled it and it's a triac.

………………………..

Edited By Grindstone Cowboy on 25/11/2020 22:09:02

Cheers, and I'm glad you didn't break it.
I was expecting to find a triac in mine, which is why I suspect the device in there when I bought it second hand has previously been replaced with the wrong item.

Thanks for looking.
I might just try bunging a diac and triac in there and see what happens.
I'll have to draw out the existing circuit first though
Bill

 

Edited By peak4 on 25/11/2020 22:38:23

[BazyleParticipant @bazyle]

Not related to your problem directly but on the subject of Dremels today on the SADMES zoom chat one of our members mentioned that the motor wires in some of these drills are connected by insulation displacement connectors which result in a nick in the wire that eventually then breaks the wire owing to vibraton. So a complete failure might be due to that. Be aware.

[Robert Atkinson 2Participant @robertatkinson2]

A l7805 is a 5V DC regulator. Most certainly the wrong device for a 240V universal motor.
Problem is you have no idea what the previous bodger did. A triac is much more likely. Have you tried contacting Dremel? you never know till you try.

Can you post a photo of what is there already?

Another option would be to use a basic light dimmer in series with the tool. (Use an earthed metal back box, proper strain relief on cables).

Robert G8RPI.

[peak4Participant @peak4]

Posted by Robert Atkinson 2 on 26/11/2020 07:51:40:

A l7805 is a 5V DC regulator. Most certainly the wrong device for a 240V universal motor.
Problem is you have no idea what the previous bodger did. A triac is much more likely. Have you tried contacting Dremel? you never know till you try.

Can you post a photo of what is there already?

Another option would be to use a basic light dimmer in series with the tool. (Use an earthed metal back box, proper strain relief on cables).

Robert G8RPI.

Yes, tried contacting Dremel UK, which seems to take you to Bosch

Hello,
Thanks for your query Sorry, we are unable to advise on component level repairs on Dremel products.

US Dremel takes you to an auto-chat, which doesn't recognise anything relevant that I type, and the email help option directs you back to the UK as I don't have a valid US address for it to check.

I've a Lidl light dimmer which does the varispeed quite well, but was just seeking to fettle the Dremel itself as the spare bedroom electronics workshop is warmer than the garage metalwork one.
I'll draw the circuit out later

Bill

[Grizzly bearParticipant @grizzlybear]

Hi peak4,

Please keep us posted.

Mine is a 300 series, willing to help, if required.

Bear..

[peak4Participant @peak4]

Thanks for the offer of assistance folks, a slight delay in the presentation.
I'm pretty sure that the incorrect device should be a Triac, though I'm not sure if the addition of the L7805CV, by a previous owner, has killed the other semiconductor, which I can't read.
I'll probably order a couple of BT136 Triacs and a couple of DB3 Diacs just in case.

Circuit diagram as far as I can tell is as below;

It all took slightly longer to draw than I'd planned.
Trace out and draw diagram on a bit of paper; Thinks I, this won't take long as it's nice and simple (except I can't read half the components)
First play with Visio 2007 on this PC in the hope of making a presentable diagram, only to find that this edition of Visio can't accept new shapes (components).
Fire up other PC with 2007 Pro, in the spare bedroom electronics shop, which does have a few suitable Visio shapes.
Try and make the upstairs PC see the network drives after the last W10 update……………………….
Draw Circuit and upload to NAS
Back downstairs, this PC has now lost all network drives again, (also post the last W10 update)
(Unfortunately this one loses the drives after every re-boot, so need to re-map every time to access; I'm still chasing this fault)
Plusnet router crashes yet again, so re-boot that to access the forum.
Open file downstair,s now that I can finally see it, and save as jpg for this forum.
Upload file and check it out in the forum album, only to find that you now can't see the lines after it's been auto resized by the software.
Edit diagram with bolder lines etc, and replace the album photo.
Reboot router again

I think I've finally got there, maybe I should just have gone to the garage and cut some metal.

Bill

Edited By peak4 on 26/11/2020 21:17:43

[peak4Participant @peak4]

Final update folks, Semiconductors now replaced with Diac and Triac and I now have a vari-speed Dremel again.

Bill

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Bill

Previous owner led you on a merry dance there !!

MichaelG.

[peak4Participant @peak4]

Posted by Michael Gilligan on 30/11/2020 14:39:27:

Well done, Bill

Previous owner led you on a merry dance there !!

MichaelG.

To be honest, trying to post the circuit diagram above was far more taxing than the repair.

Bill

[HOWARDTParticipant @howardt]

I have bought Dremel spares from a shop in Derby that comes up when I search for them in the UK. At the moment I run two, one of which I had to replace the bushes and the nylon tube spindle drive, I think that one dates back to the 90’s after my first one from the seventies gave out.

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