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How do i test a Triac? or find why the ESC of my dremel is stuck at max?

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jpoopdog

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hello

Recently my ozito rotary tool stopped working properly. right now its speed is stuck at the maximum, which causes all my drill bits and such to deform due to centrifugual force. only a few bits a meant to work at maximum speed.

The speed controller it seems is not working and as a result is stuck in the "ON" state or something, i suspect it is because of the broken triac, its the only real transistor in the whole thing. i dont know how a triac works, or how to test it. Can someone please tell me how to test if a triac is working or not so i know wether or not to replace it? otherwise, can someone explain what might cause the speed controller to do this?

later ill open it up again and get the part number i forgot to write down last time. when i did last time all i got from it was that it was a triac, and thats it.
 
Something has to generate the pulses to the triac, probably a 555 or similar circuit for PWM, or something slightly more complicated for phase angle power control, more information about the actual circuit you have is important. Ozito is a NZ brand, some members may be familiar with it, but others live in the states and may have never even seen one.

If no one else has experience with it some good quality pictures of the control board and how it's connected to the drive components would help.
 
I would bet on the Triac being shorted causing the motor to run flat out. Thats what ive found on most faulty speed controlers that run contiously.
 
This test works for most triacs I have tested, but maybe not all (depends on the trigger current).

If you use a digital multimeter, connect the meter either way around to the left most pin (heatsink face down), and the tab (or the middle pin), you should get a high resistance, 10's of kohms at least, then use a short piece of wire to connect the red meter probe (+) briefly to the rightmost pin, the resistance should drop to a few ohms and stay there even with the wire removed, after this reverse the meter probes and do the same again (red probe connected briefly to rightmost pin with test wire), you should get the same result.
If the tab of the triac is covered with plastic, or its a bta type triac with insulated tab then use the middle pin instead.

A dead triac is most often dead short giving full speed (or brightness), this sounds like your problem you could just replace it and see.
 
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Btdt

I burned 2 Dremel variable speed controllers before realizing they're under designed. Let it run wide open on its' own, but put a standard 600W dimmer as power feed to it. Since brush type AC motors are DC equivalent, a standard dimmer works ok from ~50%->100%. Been running mine 2+ years, all ok.

Not to fault Dremel, being confined to that form factor really hurts them. I've burned 2 armatures too, treating them like slender RotoZips beats Hell out of them. Note RotoZips run great on a dimmer too, just get one with high enough wattage. Wish one of them would build a unit halfway between. Flying a RotoZip make me think of a 10 yr old running a floor polisher... G.H <<<)))
 
I would fault Dremel.... Their hardware in the last 10 years is such... I actually feel better about buying generic chinese junk... oh wait that's what the bulk of Dremel hardware is made up of now!
 
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The Dremel I have uses a small ceramic stripline with printed resistors and slider taper on it. It also has a small Diac and a Triac on it. Mine was intermittent for ages, and I was (incorrectly) blaming the speed control and re-soldered it, cleaned all the connections time and time again etc. I even replaced the Brushes and the Brush Caps in desperation, all to no avail. It would work great after the service and then play me up the next time I needed it. I eventually soldered all the pluggable connections together and finally cured the problem. The mains input filter board plugs into the speed control block which in turn plugs into the motor, all with small pins and sprung Brass sockets. It's a silly design in my opinion, and one which will almost guarantee problems up the line. I have no idea if your Ozito thingy is built the same way or not, but if it is, you might want to perform a preventative modification after you fix the speed control issue :)
 
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I got desperate and went and used the tool again, and it once again was jammed in max, then i dropped it slightly, and that bump somehow brought the ESC back to life, another bumb killed it, and again, a slight whack gets it working again. annoyingly the vibrations from the motor is enough to turn the esc on and off, it seems either a soldering connection is loose, or the lead is broken inside the actual component, and out of sight, in any case, ill be going over all the parts, at least now i know nothings broken, its just a connections issue, very simple to fix!

Still, that drop which broke it in the first place, should not have been able to do so, it was like a 5cm drop, or less, and i think cheap components are to blame here. anyway, thanks for your help everyone!
 
The Dremel that broke for me was designed very poorly. Dremel offered to fix it and I said no. The design of the whole thing sucked.

I had to buy an entire kit instead of just the tool which also didn't make my day. A $10-15 external speed control would be the way to go if you wanted to keep it as a spare.
 
Nowhere in this thread did I find the model of Dremel given. They do vary. Some models are more problematic than others.

This thread is kind of old, and it seems the original problem just needed a bigger hammer or the magical drop. But, I am curious about the models involved. Here is my experience.

I have had Dremels for a very long time (about 60 years). Some of the hand tools are good, some not so good. My 380-6 is still working well, but doesn't fit any of the attachments that thread onto the front housing. The 395 Type 5 has given me good and bad (I have had 3). Recently, I got a 4000. It doesn't fit my plunge router (Bishop Cochran), but I do like the ON/OFF switch separate from the speed control. I have only had it for about 3 months, and in that short time, have had no problems.

John
 
I think the one I had trouble with was a 395. https://www.electro-tech-online.com/custompdfs/2012/09/dremel_moto-tool.pdf The issues are:
1) The bearing support - There really isn't any
2) The way the parts "drop into place" is designed very poorly. The electrical connections are not firm at all. Thus, anything that might compromise the connection such as starting and stopping or a loose connection will eventually kill the triac.
3) The speed control was a bit wimpy too. They did use a deposited resistor, but the slider isn't designed to last. HP X-Y recorder sliders were really designed well.

It seems like in the UK, you can get parts, but not in the US.

I already had a kit and lots of attachments and I had to buy them over again when all I wanted was the 4000 rotary tool. I had no reason to take the 4000 apart, but it wasn't worth me getting the Dremel repaired for free either. I had to have the Dremel ASAP and could not wait for a repair, so I had to buy the 4000.

There are lots of articles that show when drilling PCB boards shows that the Dremel has problems with runnout. It's not designed for precision in mind. One recommended replacement is Proxxon.

I also already had a storage case. I think I'm using one of these: **broken link removed**

The same guys that design the storage cases design packaging. You can't add stuff.

I have a Dewalt angle grinder where the rubber strain relief on the cord next to the body has to be bent everytime you put it into the case. It's very difficult to add blades or even a wrench into the case. I use it primarily for an unconventional purpose, the grass in the cracks in the sidewalk.
After I kill the grass I use something like this brush: **broken link removed** to remove the dead grass from the crack.

In an aside, I got a Dewalt DWD460 drill **broken link removed** for a song like $150 and I use it to drill 2" holes in the ground. It should also work well when using those 4' long flex drill bits A battery powdered 3/8" VSR works most of the time. I have a Bosch Demolition hammer, but it doesn't have a drill mode. It's great for digging in the ground with a spade. I got this http://www.toolup.com/bosch_11316evs_sds-max-demolition-hammer.aspx for a good price. I rebuilt it for $100 and it needed a few parts that were not in the standard kit. It's a useful too though.
 
Interesting. I also "had" to buy the Dremel 4000. Details are irrelevant.

Maybe there should be a thread on hand rotary tools? I was a Milwaukee guy and still have my old (1983) 4" angle grinder. More recently, I have switched to Bosch. I can't imagine a scroll saw that would offer more.

John
 
FWIW: Bosch has Service manuals for their tools which are separate from the parts breakdown manuals. I have a Bosch Jigsaw, finishing sander and demo hammer. I have a Skill belt sander and a Fein Multimaster.

I really hate when you have to "buy" a replacement because your in the middle of a job.
 
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