Fixing a Dremel® Hand Held Rotary Drill – A Step-by-Step Guide | Home, DIY & Stuff

Fixing a Dremel® Hand Held Rotary Drill – A Step-by-Step Guide

May 26, 2015


Dremel® Multipro (Model 395) Rotary Drill.

There comes a sad time when all great and trusty tools in the workshop begin to die from overuse.

Murphy’s Law states that this must occur at the most inopportune time. In the case of our ever faithful hand held Dremel® MultiPro rotary drill, this breakdown just happened to be in the middle of an important PCB shaping, drilling and cutting project.  Our rotary drilling tool was mounted as a router on top of a mini CNC machine at the time.

Dremel® Hand Rotary Drilling Tool - Exploded Parts Anterior View

Dremel® Hand Rotary Drilling Tool – Exploded Parts
(Click to see our step-by-step hand held rotary drill strip down guide.)

When the problem started, the tool motor suddenly became erratic and there were problems with the variable speed control (VSC) switch. Then, the sliding switch no longer provided any motor speed control what-so-ever.  It only provided power ON at full speed – a heat blasting 35,000rpm …. and a silent OFF.  This wasn’t at all ideal for our CNC cutting project where cutter heat control was important.

So what was our obvious DIY reaction to this? Find the cause and fix the tool ourselves of course!

You can find photos showing how the internals of our Dremel® MultiPro tool looked here.  We have also provided a step-by-step dialogue on how the tool was taken apart; how the faulty part was found and replaced AND importantly, how the hand held drill was successfully put back together again!

The problem was found to be due to a single faulty silicon chip which had failed after years of loyal service. The chip was a TRIAC (Triode for Alternating Current – Chip BT134W).  The chip was replaced in a matter of minutes and cost less than a couple of dollars. The entire DIY repair job was very quick and easy! And, it saved our aging rotary drill (come mini CNC cutter!) from the workshop graveyard.

We thought our step-by-step DIY repair diary and photos might be handy for anyone interested in the internals of rotary tools.

There are clear layouts of the tool’s internal arrangement and components, and the guide answers the question of why the tool failed on us in the first place. It also gives a few practical tips for anyone doing similar DIY maintenance and servicing on rotary tools in future.

Our DIY repair of the Dremel® MultiPro – Model 395 was a complete success. After the project, the variable speed motor control switch worked perfectly and the insides of the Dremel® tool also benefited greatly from a thorough clean and bearing lube.

 The tool now works like new!

Can you imagine the craziness of having to throw away the entire tool just because of one cheap and easily replaceable electronic component like a TRIAC chip?!

 Anyhow, with the DIY fix done, we can finally get the Dremel® back in our mini CNC milling machine and finish off the PCB cutting project we started!

Phew, another trusty workshop friend saved from flat lining…. 

(Our photos and guide to fixing the Dremel® internals is on our project page here.)


Disclaimer: We cannot guarantee the accuracy or fitness for purpose of this information for this or any other similar project.  Do not act on this information and d not attempt repairs on power tools unless you are competent in doing so. Otherwise seek a recognized and professional servicing agent. We cannot be held liable for any damage, injury, or any consequences associated with or as a result of using this information.

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