Hitachi M12V Speed Control- Help
#11
I bought a used Hitachi M12V a year or so ago.  Never used it until several months later.  The speed won't stay constant at anything except max.  At any lower setting it starts out at lower speed but the minute you engage the bit into wood it surges to max. speed and stays there whether the bit is in wood or not.  Turn it off, turn it back on, repeat.  It's useless to me as it is as I bought it so I could run large diameter bits which require lower speed. 

So I assume something is wrong with the speed controller, yes?  Anyone know how to cure it?  Thanks.

John
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#12
I expect there is a bad capacitor on the speed control board.  No experience, but that's what I would look for.  Is this one of the big, old ones, or one of the ones that look like they got abducted by aliens?
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#13
Thanks.  It's one of the big old ones in plain green.  Like this.
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#14
that's what I have too.  The controller is available at a price that probably makes it not worth it.  I didn't see a schematic anywhere. Well, actually there are way too many schematics that don't really apply.

Someone suggested bypassing the controller and using one of the $15 HF speed controls. That might be the best idea

eta: I saw your other post, and I believe the person that posted and said it was a potted module. That would mean it's really hard to repair. If you can get one, that would be great, but personally I think I could live with the HF speed control.
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#15
If it works on max, do as suggested and leave it there and get an external speed control if you need it.

That speed control dial is probably a variable resistor so I would think that could be bad as well.  Usually if they go bad you can change behavior by pushing or tapping on it.
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#16
Thanks guys.  Those are the answers I expected but was hoping for a better option.  I have a router speed controller I bought from somewhere back when.  It is a poor substitute for the modern electronic controllers, although maybe as good as the M21V had when new.  With no electronic compensation for load, the bit slows down and even stalls if you take much of a bite.  But I suppose it's better than throwing the machine away - or maybe not.  For sure I'm not buying a new Hitachi speed controller as they cost over $100.  I'd be better off putting that money towards a new, modern router. 

The moral of the story is:  I shouldn't have bought a used router.  Used stationary machines, yes.  Used power tools.  No.

John
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#17
mine is 25 years old at this point.  I don't use it much.  I don't remember when they stopped making this model. I remember it being pretty expensive for me at the time, $250?

 I would be curious if it's really potted solid with epoxy or just in a sealed module that can be cut apart with a dremel.  I guess people just give up before they try to fix the module.  The soft start is really nice, and I know what you mean about the speed regulation, it must have some kind of feedback.  I don't think that would go bad, would be a hall effect sensor.  I expect they are feeding that into a cap which is what has gone bad.  

I don't know if the potentiometer is accessible, but I suppose it's worth a try to hit it with some pot cleaner.  I don't know where you get that nowadays though.  

Someone on the other board said he might be able to give you a module, did you follow up on that?
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#18
So here's the end of the story.  I decided to buy one of the HF router speed controllers are reading from a few others that it works well.  Sure enough, it does.  To make it work with the Hitachi I bypassed the on board speed controller so that the router runs at full speed when the on/off switch is turned on.  For those that are curious, the on board controller is indeed potted in it's housing and cannot be opened. 

The router runs nice and smooth now across the speed range the HF controls to.  Full speed seems about the same with or without the controller.  The lowest speed seems higher than what my Bosch electronic router runs at, but it's still low enough that I can use fairly large bits with it.  Best of all, the speed stays pretty constant when I engage the bit into wood. 

I have another router. 

And I threw out the Grizzly router speed controller that doesn't work.  FYI, the HF controller will not work with soft start motors, nor with brushless ones.  But for old routers like the Hitachi it seems to work very well.  It cost $20 - a 25% off coupon yesterday.  

John
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#19
Yup the speed controller is too expensive.

Could you use a rheostat?
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#20
(01-03-2017, 10:44 AM)jteneyck Wrote: [snip]
And I threw out the Grizzly router speed controller that doesn't work.  FYI, the HF controller will not work with soft start motors, nor with brushless ones.  But for old routers like the Hitachi it seems to work very well.  It cost $20 - a 25% off coupon yesterday.  

John

I'm not certain but I think if you bypass the speed controller, you also bypass the soft start function as well. I had to do the same thing with a Porter Cable 8529 plunger router. The external speed controller is less convenient on a hand held machine than on a table mounted one but it works. I threw out the old speed controller and of course a couple months later read that some speed controller problems were caused by the same crappy capacitors that killed a lot of PC components. There was a fix for bad caps costing a few bucks.
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