DW788 blowing fuses

[Byron Wells]

Hey all

Bought a new in the box DW788 off a guy that bought it and never got around to using it about 6 months ago. Needless to say no warranty. Today I'm scrolling along and it just quits. First I figured maybe the foot peddle. Plugged in direct and no go. Discovered the 3 amp fuse had blown. Got a new package of them and they blow soon as I hit the switch. Any thoughts? Possible burned up motor already? Picture for attention..

Thanks in advance!

[Byronw999]

Update. Removed covers. unplugged the motor from the control board. doesn't pop fuse now but there is also no power at those terminals I unplugged when turned on

[OCtoolguy]

Have you tried rotating the motor with a screwdriver in the end of the motor? Remove the brushes and check them for excessive carbon powder. When new they do wear faster. Make sure the switch is clean of sawdust. They get dirty fast. Other than that, anything else I might suggest would require tearing it apart. 

[spirithorse]

Greetings,

If you are plugged into a long extension cord or plugged into an extension cord
that is too small for the amperage that can cause the fuse to blow prematurely.

Are you certain there is no moisture in the electrical circuit of the scroll saw?
That would also create a problem.

Let us know what you find out.

God Bless! Spirithorse

[spirithorse]

By the way, those are some fantastic ornaments!
Thanks for sharing and God Bless! Spirithorse

[OCtoolguy]

4 hours ago, Byronw999 said:

Update. Removed covers. unplugged the motor from the control board. doesn't pop fuse now but there is also no power at those terminals I unplugged when turned on

It sounds like the controller board has gone south. Just my guess based on what you just wrote. It's actually not all that uncommon. As mentioned, if you are using an extension cord that is too small, that could cause a problem.

 

[Byron Wells]

4 hours ago, spirithorse said:

Greetings,

If you are plugged into a long extension cord or plugged into an extension cord
that is too small for the amperage that can cause the fuse to blow prematurely.

Are you certain there is no moisture in the electrical circuit of the scroll saw?
That would also create a problem.

Let us know what you find out.

God Bless! Spirithorse

No extension cords at all. Plugged into foot pedal which is plugged directly into the outlet. Cant be moisture. Here in Florida it's humid all the time. I have a dehumidifier in the area of the scroll saw that runs 24/7

[dgman]

Have you tried disconnecting the foot switch?

[Byron Wells]

1 minute ago, dgman said:

Have you tried disconnecting the foot switch?

Yes, 1st thing I did when it quit. Still blew new fuses when I used the DW switch

[spirithorse]

Unfortunately, I think octoolguy Ray may be correct.
A new circuit board would probably be about 1/3 the price of a new saw
so, it's a difficult decision to make. Of course, you would definitely want to
be absolutely certain the circuit board is the problem before swapping out parts!

There are a lot of videos on YouTube about How To Test a Printed Circuit Board Assembly
(PCBA) but, I did not see one specific to the DW788.

This site DeWALT Scroll Saw | DW788 | eReplacementParts.com lists the board abt about
$94 and these images came up in my search engine for other suppliers.  dw788 scrollsaw circuit board - Bing

I have used the eReplacementParts.com site with good results and other forum members have recommended it
in the past also.

Good luck and God Bless! Spirithorse

[OCtoolguy]

42 minutes ago, spirithorse said:

Unfortunately, I think octoolguy Ray may be correct.
A new circuit board would probably be about 1/3 the price of a new saw
so, it's a difficult decision to make. Of course, you would definitely want to
be absolutely certain the circuit board is the problem before swapping out parts!

There are a lot of videos on YouTube about How To Test a Printed Circuit Board Assembly
(PCBA) but, I did not see one specific to the DW788.

This site DeWALT Scroll Saw | DW788 | eReplacementParts.com lists the board abt about
$94 and these images came up in my search engine for other suppliers.  dw788 scrollsaw circuit board - Bing

I have used the eReplacementParts.com site with good results and other forum members have recommended it
in the past also.

Good luck and God Bless! Spirithorse

I did the same research and found exactly the same thing. It's a pricey part but what are you gonna do? Gotta fix it. It's probably a ten cent part on the circuit board. Do you have any friends who are into electronics? If it blows a fuse that fast, it's probably a short somewhere but who knows where? Maybe you can take the board out and use a magnifying glass to inspect it. Possibly see the shorted part. Somebody must repair stuff like that.

 

[teachnlearn]

If you have opened it up, examine the wires closely, look for any that are bare, touching each other or to the frame. The build goes down a factory line so fast they could have over stripped wires or used a wire that was damaged.  Light the area with bright lights and examine with a magnifier. Check the board for loose wire. Blow the board and all parts with shop or canned air. Odd the board would be bad right off. There should have been a check at the end of the factory line to run it for a few seconds. There are other checks, but it would take a few electronic tools. RJF

[OCtoolguy]

1 hour ago, teachnlearn said:

If you have opened it up, examine the wires closely, look for any that are bare, touching each other or to the frame. The build goes down a factory line so fast they could have over stripped wires or used a wire that was damaged.  Light the area with bright lights and examine with a magnifier. Check the board for loose wire. Blow the board and all parts with shop or canned air. Odd the board would be bad right off. There should have been a check at the end of the factory line to run it for a few seconds. There are other checks, but it would take a few electronic tools. RJF

@teachlearn, he has been using the saw. He cut all those ornaments that he showed in the first post. It's been working and suddenly went bad. Gotta be something vibration related.

 

[Dan]

The last variable speed saw I had had the control board go out. The motor seemed to test good so I got the control board and replaced it. It ran fine for a few weeks then that one went out. After some research it was recommended to replace the board and motor at the same time as a bad motor can blow the board. The saw wasn't worth putting money into and I was wanting to upgrade so I bought my Delta P-20. No circuit board to go out. That was 15 years ago. 

[ike]

Ir could be that the motor armiture is cloged with the carbon  from thje brushes. Remove the brushes and take an air hose and blow the motor out. The proper  way is to take the motor apart and clean it. if you not carful you could rulen the motor. I , I worked with could do it because I worked with motor for 25 yeara.

IKE

 

[teachnlearn]

1 hour ago, octoolguy said:

@teachlearn, he has been using the saw. He cut all those ornaments that he showed in the first post. It's been working and suddenly went bad. Gotta be something vibration related.

 

Since its not on my bench with electronic test equipment, I recommended the simplest no equipment visual inspection. In my short life I covered a whole group of jobs including industry work. I've seen some strange things which most repair people can relate too. Uninsulated wires can be a pain to trace, ESPECIALLY with running machines and cars. All it takes is the wire to vibrate and touch, grounding out. Spent hours and hours going through cars trying to find the shorted, intermittent wire. After a visual inspection, its down to electrically troubleshooting, or start replacing parts til it works. Could be one of these other recommendations. Once there is a good look over, its down to self repair, send for repair, scrape and buy new.

As to tracing electrical wire in cars, I've seen recommendations to just buy a whole wiring harness and replace the whole thing.RJF

[OCtoolguy]

26 minutes ago, teachnlearn said:

Since its not on my bench with electronic test equipment, I recommended the simplest no equipment visual inspection. In my short life I covered a whole group of jobs including industry work. I've seen some strange things which most repair people can relate too. Uninsulated wires can be a pain to trace, ESPECIALLY with running machines and cars. All it takes is the wire to vibrate and touch, grounding out. Spent hours and hours going through cars trying to find the shorted, intermittent wire. After a visual inspection, its down to electrically troubleshooting, or start replacing parts til it works. Could be one of these other recommendations. Once there is a good look over, its down to self repair, send for repair, scrape and buy new.

As to tracing electrical wire in cars, I've seen recommendations to just buy a whole wiring harness and replace the whole thing.RJF

I used to sell a short circuit locator that worked well on cars. It had a 15 amp circuit breaker that would open/close every few seconds and all you had to do was follow the wire harness with an inductive ammeter and watch the needle fluctuate. When it stopped fluctuating, you had passed the spot of the short/open circuit. Not something that would work here but same idea. 

 

[Byron Wells]

Thanks all!! I'll open the top cover and check wiring going up to the switch and recheck all the other wires. I did pull the circuit board and nothing visibly scorched. 

Yes, I've been using saw about 7 months. and done a lot of scrolling trying to build up inventory. When it quit it kinda acted like it had no power and was struggling to stay running for a few seconds then popped the fuse. 

Question:::: How do you get the brushes out? I remove the caps and they don't want to come out. When I've replaced brushes in past tools they all had a spring attached and just popped out.

 

Motor does spin freely. I do have a circuit board ordered just in case. $85 wasn't bad. I've always been one to have spare parts on hand for things (ex wife said I was a hoarder, but whatever. LOL)

My quandary is this: I'm retired and trying to start a small glass and wood gift/souvenir business here in Florida because Social Security sucks. Lots of snowbirds and vacationers that love craft fairs etc. I could order a Pegas but waiting until April for it is kinda out of the question. Other alternative is to grab a Delta  for 381.07 off amazon and get the 4 year extended warrantee so at least I can get it fixed. I'm on a fixed income and dont have money for both. Last choice would be using my old tired 2 speed Dremel I've had for about 20 years.. Thinking NOOO! 

[teachnlearn]

Motor brushes do come with the springs slid on. If the spring comes out and the carbon brush doesn't its a game of retrieval. Long needle nose pliers, a small long screw driver, any tool in your collection that would fit to grab and pull it, good excuse to buy a few jeweler pliers. A last resort would be to drill a small hole in the center and go up sizes to fit a long screw. Screw in the hole and pull the brush. Have a replacement on hand which will give you an idea of what your chasing. The drilling could split the brush or just be better practice to put in new rather than have a set of brushes with holes. Double check there are no brush pieces left in the motor. RJF

[teachnlearn]

15 hours ago, octoolguy said:

I used to sell a short circuit locator that worked well on cars. It had a 15 amp circuit breaker that would open/close every few seconds and all you had to do was follow the wire harness with an inductive ammeter and watch the needle fluctuate. When it stopped fluctuating, you had passed the spot of the short/open circuit. Not something that would work here but same idea. 

 

Seen versions on those locators. Don't have any wire problems to justify the purchase. BUT I WANT THEM! RJF

[OCtoolguy]

5 hours ago, teachnlearn said:

Seen versions on those locators. Don't have any wire problems to justify the purchase. BUT I WANT THEM! RJF

They were a cheap tool that saved a ton of time. I think when I retired, they were still about $30 for the whole setup.

 

[Dan]

Toothpick with some gum (or any sticky substance) may help to retrieve the brushes. 

[OCtoolguy]

Knowing that you have stuck brushes makes me wonder whether it could be that the motor was becoming jammed by a broken brush and causing it to overload that fuse. 
Also, as another suggestion, since you live in Florida and so does @amazingkevinKevin, he always has a dozen or so Dewalts laying around that he uses for parts and rebuild saws. He might be in a position to sell you one of them and you could do a rebuild on it and have another Dewalt for your business. Having 2 of the same machine makes sense to me. 

 

Edited February 19, 2021 by octoolguy

[teachnlearn]

3 hours ago, octoolguy said:

They were a cheap tool that saved a ton of time. I think when I retired, they were still about $30 for the whole setup.

 

Models I saw had the fuse system, but also had a signal 'SOUND' injector. It could be put on a wire or sets of them and a detector could trace the signal down the wire to a ground or broken wire. The was around the 100 range plus accessories.

Also looking at a similar system that plugs into house outlets/ lights and a detector gives the specific breaker. Thinking of getting one if we ever find a dang house I have no idea what anyone has done to the electrical system, so I'll trace and label every system. RJF

[OCtoolguy]

4 minutes ago, teachnlearn said:

Models I saw had the fuse system, but also had a signal 'SOUND' injector. It could be put on a wire or sets of them and a detector could trace the signal down the wire to a ground or broken wire. The was around the 100 range plus accessories.

Also looking at a similar system that plugs into house outlets/ lights and a detector gives the specific breaker. Thinking of getting one if we ever find a dang house I have no idea what anyone has done to the electrical system, so I'll trace and label every system. RJF

I also sold that one you speak of. If I recall it ran about $100 or so. I sold some stuff from an out by the name of PowerProbe that was great for electrical troubleshooting on automotive stuff. I've not sold anything for AC.