Dewalt 788 problem

[Grumpy Old Bear]

Ever have one of those days where you just don't want to do anything? I had that last week. I had a blade tension issue with my Dewalt 788. I got that fixed and that's when I got hit by the Lazy Bug. Over the weekend I went to the shop and started cutting. I went to adjust the speed a little and it went crazy fast. I slowed it back down and barely touched the speed knob again and it went bonkers for a second and than stopped. I thought the foot switch may have died, but that was not the case. I thought one of the wires came off the switch, but that wasn't it either.

Has anyone had this type of problem? Please tell me it is a simple, AND CHEAP fix.

Thanks, Jim

[UncleApple]

When you say "stopped", it stopped running fast or stopped entirely?  If stopped entirely, it may be the DW788 fuse or the foot switch.  Have you tried plugging the saw directly into the outlet?

[JOE_M]

If you take the footswitch out of the equation and plug it directly into the wall does it start? If not, then as UncleApple says it could be the fuse. I blew one a couple of months ago doing something stupid.   You can buy a 5-pack at most auto supply stores for very cheap.

Edited May 22, 2017 by JOE_M

[CharleyL]

The speed control in the DeWalt scroll saws is not sawdust proof and can get dirty easily. One easy fix is to turn the saw off and then turn the speed control back and forth from stop to stop about 6 or more times. Then turn the saw back on and slowly increase the speed to see if the "bad spot" is now working properly.

A second way is to try blowing out the speed control using one of the "Canned Air" type computer cleaners or an air nozzle on your air compressor (but make certain that the air compressor isn't shooting any condensate water before doing this). You will need to remove the black cover housing the speed control and the power switch to do this. The side of the control near the wire connections has an open area where you need to use the air stream to blow the control out.

If these fail you will need to replace the speed control potentiometer. Unfortunately, DeWalt doesn't sell this part alone, They want you to buy the entire speed control electronics board that includes this part for about $68. But the speed control part alone can be purchased at electronics supply houses for just a couple of dollars. It's just a 10,000 ohm linear taper potentiometer with a flat on the shaft (the DeWalt speed control knob has a D shaped hole in it), and it sells for $2-4 or you can get a completely sealed version for about $10 and never have dust and dirt problems again. Some of these potentiometers come with long shafts that require a hack saw to cut off for the correct length. Just mark it and cut it off at the same length as the original part.

Installation requires soldering 3 wires. Be careful to only remove one wire at a time from the old potentiometer and solder it to the same terminal on the new potentiometer. They absolutely need to be placed on the correct positions for the control to work correctly.

 

Charley

 

[MrsN]

Charley, thanks for posting this! One of the saws at my schools is doing the same thing. I just kept blowing it out but would rather fix it for good. Thanks!!

[ike]

I don't know if you use a foot peddle. If you do when you get this fixed turn on the switch put some tape over the switch to seal out dust.go and buy a foot switch the cost is about $25 or you can sometimes find them at Harbor  Freight for about $15 ( I son't know how good they are0 I bought mine at wood supply for $25  3 years ago.

IKE

[Grumpy Old Bear]

I have used a foot switch for the last 8 or 9 years, I couldn't see myself cutting without one. I have tried plugging the saw directly into the outlet and I still get nothing, so I am hoping I blew a fuse.

I do one more favor to ask: does anyone know how to reattach the blower tube to these Dewalt saws? I have not been able to just snap the tube on. I have wrapped a bunch of electrical tape around the hose and than put a spring clamp on the tape to tighten everything up enough to keep the tube off the wood.  Any suggestions?

[JOE_M]

38 minutes ago, Stupid Donkey said:

does anyone know how to reattach the blower tube to these Dewalt saws?

Mine broke the one link where it connects to the saw. I threw that link out and heated the "new" end with a heat gun (like for shrink tubing) and it snapped on easily, stayed put when it cooled.

 

[Grumpy Old Bear]

Thanks Joe. I'm going to give that try, after I get the saw running again. I appreciate all the help I have gotten with these problems. 

[CharleyL]

It's best to heat those links in a cup of recently boiled water. This softens the plastic enough to push them on or together without cracking them. Heating them with a heat gun risks the possibility of over heating them. If you over heat them you will never be able to keep them attached. It's easy to crack one in use. If the linked hose won't stay where you want it, look closely at the link seeming to be too loose. You will likely find a small crack. Warm it and remove this cracked link, then while warm, push the good pieces together without the cracked link. Industrial Supply's like Grainger, McMaster Supply and similar carry lengths of these, so if your air hose gets too short, just buy some more and add to your existing line. They offer several sizes, so be sure to take at least on piece with you to match it..

Charley 

[amazingkevin]

13 hours ago, CharleyL said:

The speed control in the DeWalt scroll saws is not sawdust proof and can get dirty easily. One easy fix is to turn the saw off and then turn the speed control back and forth from stop to stop about 6 or more times. Then turn the saw back on and slowly increase the speed to see if the "bad spot" is now working properly.

A second way is to try blowing out the speed control using one of the "Canned Air" type computer cleaners or an air nozzle on your air compressor (but make certain that the air compressor isn't shooting any condensate water before doing this). You will need to remove the black cover housing the speed control and the power switch to do this. The side of the control near the wire connections has an open area where you need to use the air stream to blow the control out.

If these fail you will need to replace the speed control potentiometer. Unfortunately, DeWalt doesn't sell this part alone, They want you to buy the entire speed control electronics board that includes this part for about $68. But the speed control part alone can be purchased at electronics supply houses for just a couple of dollars. It's just a 10,000 ohm linear taper potentiometer with a flat on the shaft (the DeWalt speed control knob has a D shaped hole in it), and it sells for $2-4 or you can get a completely sealed version for about $10 and never have dust and dirt problems again. Some of these potentiometers come with long shafts that require a hack saw to cut off for the correct length. Just mark it and cut it off at the same length as the original part.

Installation requires soldering 3 wires. Be careful to only remove one wire at a time from the old potentiometer and solder it to the same terminal on the new potentiometer. They absolutely need to be placed on the correct positions for the control to work correctly.

 

Charley

 

 

You sure know a lot of things about dewalts and specs of them,Thanks for the info!

 

[hawkeye10]

6 hours ago, amazingkevin said:

 

You sure know a lot of things about dewalts and specs of them,Thanks for the info!

 

Kevin "CharleyL" has a great wealth of knowledge. He has helped me several times on the "Router Forum" as well as others. I really wish he was my next door neighbor.

[CharleyL]

Volume controls on old radios and TVs  are the same type of part, but have what they call an "audio taper" which is a kind of logarithmec rate of change of the resistance of the control as the knob is turned. The control used in the DeWalt 788 is the same kind of part, but it has a linear rate of change in resistance. In both parts there is a resistance material and a wiper that moves along it as the shaft is turned. Any dirt or corrosion of the wiper or the resistive surface will cause "bad spots". When the contact point of the wiper passes over this spot. A sudden change in the resistance will cause noise in the radio or TV sound when the volume knob is turned  and the speed control of your DeWalt 788 will suddenly speed up or slow down when the speed control has a bad spot in it. Turning the knob to run the wiper back and forth over this bad spot many times will sometimes wipe the dirt or corrosion off of the resistive material for the control to work properly again. Sometimes it needs more than just wiping. Thats where a contact cleaner solvent is needed to disolve and break down this bad spot. Sometimes even this doesn't work. Controls like this in a woodworking machine usually suffer from saw dust causing the bad spot, and a bladt of air will blow it away, but if the tool is in a damp location, the dampness can cause corrosion of the surface.  In any case, if these methods don't solve the problem, replacement of the control is the only remaining option.

Charley 

[Grumpy Old Bear]

2 hours ago, hawkeye10 said:

Kevin "CharleyL" has a great wealth of knowledge. He has helped me several times on the "Router Forum" as well as others. I really wish he was my next door neighbor.

Like Don (Hawkeye10) said, I wish you were my neighbor. You definitely have a great deal of knowledge stuffed in your head. I would like to thank each and every one of you who have offered tips and advice. I did find out that the fuse was blown. My assistant (wife) will pick up some fuses today for me. I will attempt to work on the blow tube tonight after I get the new fuse installed. 

Edited May 23, 2017 by Grumpy Old Bear

[UncleApple]

On 5/23/2017 at 8:40 AM, Stupid Donkey said:

Like Don (Hawkeye10) said, I wish you were my neighbor. You definitely have a great deal of knowledge stuffed in your head. I would like to thank each and every one of you who have offered tips and advice. I did find out that the fuse was blown. My assistant (wife) will pick up some fuses today for me. I will attempt to work on the blow tube tonight after I get the new fuse installed. 

Glad to hear that it was only a fuse & that you'll be operational again soon!

[CharleyL]

The beauty of this forum and the internet is that it allows all of us to be next door neighbors to each other, and to openly share information with each other rapidly, no matter where we live or happen to be. I have made several very close friends in many places across this country and around the World. I consider them to be some of my best friends and neighbors, but I have never even met them face to face. We are truly lucky to live in an age where we can freely share information instantly with each other no matter where we are located  in the World.. I hope I never have to relive the past in the time before the internet again.

I'm a member of a new form of woodworking club, "A Virtual Club" thanks to the internet. This club doesn't have any meetings or charge dues to be a member. They only have one formal fifteen minute meeting each year, to elect the new officers for the coming year, and it's held as part of the annual club picnic. A very profitable raffle has provided the funds to pay all of the club's website and  annual expenses, and there are well over 6,000 members in this club now. We share information with each other through the club website, much like we are sharing information with each other here. This club is about 10 years old now and growing every day.

A few years ago the club bought a trailer and filled it with woodworking tools all paid for from the raffle funds and donations.We now have an Outreach Program where Volunteer members go with the trailer to any group who would like to get started in woodworking, to community fairs, and other places, to promote woodworking and help people explore the fun of woodworking,. We also participate in the Wounded Warrior Program, taking the trailer and volunteer instructors to military bases in NC. All of this is provided by the club free.

If you are interested in seeing our club and learning more, go to " www.ncwoodworker,net" and look around. I've seen where our website sometimes has more visitors than members logged on.to it. We are being looked at from around the World.  With the internet and this Virtual Club format, being a club member is easy. You can be as active or as laid back as you want to be, and you can remain a member without it costing you any money at all, or you can donate both your time and/or money to help the club grow. We love to post pictures of our work and help each other solve problems with all kinds of woodworking, where here at this Forum we tend to do the same, but here we generally stick to just scroll saw related subjects. Here at Scroll Saw Village we are sort of a specialized version of this club, but we don't do the Outreach Training or other face to face get-togethers that we do in Nc Woodworkers. In the past 2 years small groups of us living near each other have begun getting together for monthly luncheons, where we meet each other face to face, talk woodworking, show off our latest project, or talk about whatever subject seems to be of interest that day. These lunches are open to all members, friends, wives or husbands, and even to anyone who shows up and wants to eat and join us in the subject being discussed. The annual club picnic is really just a big version of this, but with the culmination of the raffle, the annual election, and the raffle and door prize drawings.

My intent in posting this is to get other woodworkers started  in thinking about creating other clubs similar to ours around the World. Look at what we are and then begin a "Virtual" club of your own with other woodworkers in your general area. The internet makes clubs like this work much better than most local traditional clubs that I've ever belonged to. 

Charley