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router variable speed stuck at slowest speed

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Forum topic by justbob posted 656 days ago 1560 views 0 times favorited 13 replies Add to Favorites Watch
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justbob

14 posts in 734 days


656 days ago

I have a Porter Cable 890 router the variable speed controller has stopped working and it only runs at the slowest speed. The replacement part costs $100 I only paid $200 for the whole package. Can I buy an after market speed controller to get it to run at top speed? I’m guessing no so can I safely bypass the one in the router if so I need to know how to do it. In other word which wires need to go where.


13 replies so far

View pintodeluxe's profile

pintodeluxe

3335 posts in 1449 days


#1 posted 656 days ago

It sounds like the armature assembly has failed. Usually it fails at full speed, but not always.
I wouldn’t guess a secondary speed controller would help. This is a known problem with the 890 model.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

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justbob

14 posts in 734 days


#2 posted 656 days ago

One thing I forgot to mention was that it will randomly go from low speed to high speed run for a few minutes and then go back to low speed.

View bondogaposis's profile

bondogaposis

2496 posts in 987 days


#3 posted 656 days ago

I’d go for a new router, stuff wears out.

-- Bondo Gaposis

View EEngineer's profile

EEngineer

890 posts in 2249 days


#4 posted 656 days ago

I don’t know whether I would blame the armature. To me this sounds like a speed controller failure. It it is the speed controller, there might be a simple solution.

A while back (thread here), I answered some questions about soft-start and a variable speed controller for a motor. His solution was to bypass the soft-start and add an external variable speed controller.

If you want to save the router and some money, your solution might be the same. You can pick up an external variable speed controller for routers for ~$20. If you bypass the speed controller in the router (the thread I mentioned above has a description of what he did to bypass the soft-start circuit), then you can use an external speed controller. This is also a quick way to test whether the speed controller or the armature is the problem. Bypassing the speed controller won’t hurt the router – it will just run at full speed anytime you switch it on. Routers worked like this for years before they starting adding speed control.

-- "Find out what you cannot do and then go do it!"

View wunderaa's profile

wunderaa

189 posts in 838 days


#5 posted 655 days ago

If you’re adventurous, you can try a few things.

Potential Failure Causes
- Dust Build Up Inside Top of Assembly Interfering with Feedback (Unlikely, but easy to check)
- Broken Speed Feedback Magnet
- Bad Speed Control Board

Take apart the top of the router revealing the top of the motor shaft and electronics (you may have another layer to remove below the control board before you get to the top of the shaft). Blow out the assembly with compressed air and see if that does the trick. Again, unlikely.

When you open the top of the assembly, you’ll see the control board and the top of the motor assembly. If you look at the top of the motor shaft you should see a magnet mounted to the shaft. Most likely, this magnet has broken. It’s this magnet that, when spinning, generates a current in a coil of wire that surrounds it (Faraday’s Law, anybody!?). That current is proportional to the shaft speed. That current is fed into the controller and utilized in a feedback loop. I’m guessing that they may have designed the unit to fail such that the tool can still be used, but we can find out for sure soon.

If the magnet is broken, you can either find a replacement (try www.ereplacementparts.com), or go about converting your router into a still-useful single-speed unit with an external speed control.

What I would try from there is to remove the magnet completely from the shaft. Put the unit back together and see if it still works. If it goes up to full speed, then they have engineered the unit to fail at full speed and you should be good to go. If it’s dead or runs at low speed, we can move on to the next step.

At this point, you can either junk the unit or grab a soldering iron and some shrink tubing. The fix from here-on is to bypass the control circuitry completely. In the safest manner possible, connect the two wires leading from the on/off switch to the two wires going to the brushes, disconnecting all power wires from the control board (although there may only be one power wire routed through the board). If you sent a picture of the control board itself, I may be able to tell you what two pins to solder together on the board to effectively accomplish the same thing, but that’s about the best I’ve got without seeing the unit. That may be as simple as wiring two pins from the triac together, but can’t tell without a picture.

Assuming that goes well, you should be able to run the unit at full speed. You can then purchase an external speed control unit from Rockler or elsewhere to control speed if needed.

Hopefully this helps or at least gets you headed in the right direction.

View HorizontalMike's profile

HorizontalMike

6928 posts in 1550 days


#6 posted 655 days ago

”...Blow out the assembly with compressed air and see if that does the trick….”

Well worth the effort to use compressed air. This worked on my old Dremel tool, kinda like a mini-me router ;-)

-- HorizontalMike -- "Woodpeckers understand..."

View 404 - Not Found's profile

404 - Not Found

2544 posts in 1605 days


#7 posted 655 days ago

When you open the top of the assembly, you’ll see the control board and the top of the motor assembly. If you look at the top of the motor shaft you should see a magnet mounted to the shaft. Most likely, this magnet has broken.

^ Worth checking – I have experienced this on a Dewalt DW621 Router, however, it was stuck on full speed.

View NiteWalker's profile

NiteWalker

2710 posts in 1213 days


#8 posted 655 days ago

Exactly; if the magnet broke the motor would be stuck on full speed, as is the case with both of my dewalt 618’s.

-- He who dies with the most tools... dies with the emptiest wallet.

View justbob's profile

justbob

14 posts in 734 days


#9 posted 655 days ago

thanks for the input I’ll try all of the suggestions tomorrow

View wunderaa's profile

wunderaa

189 posts in 838 days


#10 posted 654 days ago

curious to hear how this turns out!

View justbob's profile

justbob

14 posts in 734 days


#11 posted 649 days ago

just completed the bypass router runs at top speed since that is how I use it almost exclusively its not a big deal, if i ever need to raise a panel i can go buy an aftermarket speed control. the only feature I kind of miss is the soft start.

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wunderaa

189 posts in 838 days


#12 posted 649 days ago

Awesome!

View Howie's profile

Howie

2656 posts in 1559 days


#13 posted 649 days ago

I’ve been having the same problem with my Makita 1101. Been a good piece of equipment.Thanks to some of these suggestions I’m going to try and salvage it rather than buy a new one.

-- Life is good.

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