Hand Router teardown and diagnosis


The mastercraft hand router has been broken (not turning on) for a while now so I thought I’d take a look as it is probably our most useful router and has the router table too.

I got a good bit of diagnostics done but could probably use a bit of input on the next steps.

Here’s what I did (not plugged in obviously):

  1. Checked the power cord for continuity using a multimeter and undoing the wires from the switch. - FINE

  2. Checked the switch for continuity using a multimeter. - There seems to be a short on one of the switch connections.

  3. Checked the router for continuity (again with a multimeter) - There was no current so I had to look a bit further.

  4. Opened the top of the casing and tested all the wire connections for continuity. FINE

  5. Isolated the problem to the speed control board. There only seemed to be current at speed 7, so there is a problem there but it should at least work at 1 speed. Reassembled and had continuity throughout the router.

  6. The brushes are in a pretty bad way but don’t seem to be the cause of the issue.

So I guess the question is, would it be worth getting a replacement switch (pics below) and where on earth do you get one of those?


(also whoever took it apart previously, forgot to put back some of the screws and the depth setter)


Can we open the switch and fix the innards? Thanks for troubleshooting and for the excellent write up!

p.s. we also may be able to find the part on reliableparts.ca or some similiar service.


@Janet the switch has springs clips, which look like they were designed not to be reopened. The case may break, or just the clips but nothing a bit of super glue wouldn’t fix. Just didn’t want to go to that step until there was an idea of how cheap or easy to get a replacement might be.


Thanks @hughl87 for that thorough investigation!

Looking at the diagram on the switch, it seems to be a DPST switch, so basically two switches in one. From the second picture, it seems that the switch is between the cable and the board, so one of the two poles is probably used to switch the phase. I’m curious, what is the other pole used for? Switching neutral maybe?

Also, which of the two is shortend?


Looking at the pics again, it seems that the switch is indeed connected to both phase and neutral.
If one of the poles is permanently closed, the router should still work, as the current can get through. Not sure if it is still up to code, though.

I guess there is another problem somewhere.

Looking at the board, this seems to be a simple TRIAC based circuit. Like the one described at the end of this article: http://www.electronics-tutorials.ws/power/triac.html. The little blue component beside the label is probably the DIAC. The TO-220 is the TRIAC.

I guess the TRIAC is burned out, since it should really have a heat sink:

The label on the router says it uses 7 A under full load. From datasheets of some randomly selected TRIACs that would fit the specs, all have a 7 W loss at 7 A. They also all have a junction to ambient thermal resistance of about 50 C°/W, and a maximal junction temperature of 125 C°. So, under full load the junction will heat up to about 350 C° over ambient temperature, about three times over the limit. Probably worse, since there isn’t much airflow. Basically, if this thing is run at more than 20-30% load for long enough, the TRIAC will burn out. Seems a likely scenario for what might have happened.

Replacing the TRIAC should be fairly simple. If there is some space for a heat sink, that would be a great improvement of this tool. Would be nice if someone would know a way to verify my theory first, though.


Thanks Stefan,

I believe 3-4 is not working. On the other stuff you’ve stepped outside my comfort zone so I’m going to smile and nod :slight_smile: and run off and read that tutorial. I thought of a good way to open the switch with minimal damage so will check that next.


Sorry, I geeked out a bit :smiley:

What I wanted to say is that the switch might not be the only thing that is broken. One of the other things that might be broken is this component:

which can easily break because the manufacturer saved the 50c for a heat sink.

I could be wrong though. It’s just a guess. Maybe make some close up pictures of this thing when you have the router open anyways.

I’m curious what you find in the switch!



So I opened the switch to have a look… it did not look good

After clearing out the crap you can see lots of nice burn marks and the connectors are almost completely wrecked, also I have a lot of respect for the person who first assembled that cos it is a nightmare to put back together. So now I think we’re definitely looking at a new switch.

Any suggestions on how we might get one? As its mastercraft there doesn’t seem to be a vast support network and its an old model too.


This switch is just a simple on/off right? I wonder if we could could find a similar component if we can’t find an exact replacement part? Are there any part numbers on the switch? If I can make it down on Thursday I’ll have a look. Also thanks for cracking that sucka open!


From the images,

250V~ 4A


Side B
7A 120V~



It has to be in here somewhere. :smiley:

Hey @packetbob you’re good with this stuff. Any idea?


Is it possible to jumper across the switch, make sure that’s the only issue?


Good point. You were thinking might be a variac issue right?


Yeah I guess we could just solder the connector across the top section of the switch. Although if someone with more wiring and electrical knowledge than me would be willing to supervise that it would be appreciated. A good outcome would be a working router, a sort of minimum outcome would be me not managing to electrocute myself with some dodgy wiring :slight_smile:



We also have some toggle switches in the components, probably one that matches or exceeds the specs of the switch. If we can make one fit (possibly with some clever dremeling) we could just call that a day.