Dewalt 788 lost variable speed

Brian Downing

New member
Messages
3
Location
Philadelphia
I'm very new to scrolling and recently purchased an older Dewalt 788. Turns out the variable speed is no longer working.
I've been reading up on it and it seems like it can be a very expensive fix and probably not worth it for an older saw.
Everything else seems to be working ok and I was going to do a rehab based on a youtube video I watched.
My question is...would a foot pedal work to control the speed?
Any advice you can give would be greatly appreciated!!
 

Chuck Ellis

Member
Messages
5,407
Location
Tellico Plains, Tennessee
I can't give you any info on your saw... my scroll saws are both Dremels... one is a smaller that is single speed, the other is larger with a two speed control, fast and slow.... the slow is faster than the fast.... I talked to an electrician that does small electric motors... he said it likely was a capacitor that went out and was likely proprietary so it would be pricey to fix since I would have to order the cap from Dremel... not worth it to me, haven't used it in years, so it's now sitting on a shelf as a boat anchor.
 

Vaughn McMillan

Administrator
Staff member
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32,921
Location
ABQ NM
Welcome to the forum, Brian! :thumb: It looks like the Dewalt 788 is 1.3 amps, so I believe something like this 1.6 amp speed controller would work:

 

Charles Lent

Moderator
Staff member
Messages
316
Location
Central North Carolina
Frequently, the speed control potentiometer of the DeWalt 788 will fail. New ones can be found quite reasonably. If I remember correctly, they are 50K ohm linear taper. Some of the commonly available replacements have long shafts, but a hack saw fixes that.
There is a connector in the wiring between the speed control and the pc board, so just the speed control can be removed quite easily.
I lay the new and old side by side on the bench and move one wire at a time from old to new, soldering each in place as I go, then return it to the saw and test it. The pc board itself is in the bottom of the saw. Removing the screws from the non motor side will let you get to it. A good visual check might find the problem, if it's a component on there. It's easy to replace just one component, if you can solder and do electronic type work. NEVER use acid core solder or solder paste on an electronic circuit. Rosin core or rosin solder paste is the required material. I have repaired several of my woodworking club's Dewalt 788 scroll saws, but usually they have bearing wear problems long before speed control problems. The bigger bearings and the pivot bold for the rocking arm back by the motor and on the motor shaft are what usually require replacement long before the bearings in the front part of the saw wear out.

Foot control pedals that I have and have used are on-off switches and don't help with speed control. You also don't want two speed control units in the same motor control circuit. They won't like each other.

Charley
 
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