DeWalt DW433 Belt Sander runs intermittently

[Stephen Tashiro]

Who can tell me something about simple tests that can be done on the electrical circuits of the DeWalt DW433 Variable Belt Sander?

I bought one "refurbished" from etools via Amazon. It ran for about 5 minutes of on-and-off work and then then the motor would not run. I took off the plastic side panel over the belts and took apart the handle. I tested for continuity between the prongs of the powercord and the wires into the switch. That was OK. I tried testing for continuity across the terminals of the switch when the switch is pressed and that seemed OK, however I am not sure of what's in that circuit.

I put the sander back together and it ran! It ran for about 5 minutes again and then quit running. I let it sit unplugged for several hours and tried it again and it didn' t run. I've taken apart the handle again, but what simple things should I test?

In addition to this sander, I have a new DW433K that works fine. So my main interest is learning how to repair the used sander. I'm not in a hurry to use it and I don't plan to send it back for exchange.

[qdea]

Stephen,theres a little black electronic module that controls the speed tru the selector on the side of the handle,that may be the part that is malfunctioning,however this is located in the main body near the top of the handle,for you to get to it you'll have to basically take the machine apart.first take the handle off,(turn it on the side wit the belt facing you).then remove the 3 longest screws on the side,also the 2 near the bottom of the handle.turn the side lever to where you remove the sanding belt for slack and then take the 2 halves apart,you shuold see the black module screwed to one side,

additional to that you might only need new brushes,which are located on the other side of the machine.

Good luck

Quincy
Guyana
South America

[Stephen Tashiro]

Thanks for those directions. Before I remove the control module, I'd like know if it is bad. I've taken the handle apart. I can see the connector to the control module. I can see the male side (4 pins). Are their any simple tests (like measuring the resistance between certain pins) that I can do to determine if the module is bad? Or is there a way to bypass the module to see if the sander runs?

One interesting question is how does this module work?

[Stephen Tashiro]

I did further disassembly. Took off the belts, the blower. The metal halves came apart after removing two long bolts. (The nuts are captured in holes on the opposite side of the planer, so you must watch that they don't fall out and get lost . I had already removed a short bolt that was involved near the "tail" of the planer when I removed some of the plastic parts.)

The speed control module is indeed in the metal part of the handle. It has no mechanical connection to anything. The only electrical connection it has is the connector that was visible before I took the handle apart. It says :
615050-00
MADE IN CHINA

I asked about my problem on the dutchforce electronics forum in the analog electronics general section. A poster said that the control module is probably based on a thyristor. Maybe it is like figure 1003.9 in the document: http://www.littelfuse.com/data/en/Ap...tes/AN1003.pdf
I don't see a non-destructive way to take this module apart.

I removed the plastic cover of the motor (looks like this could have been done without any of the previous disassembly). It says:

P/N 393742-00
PA6/G33

which isn't very informative. It has a commutator and two brushes. I assume it is an AC motor. So I'll try to bypass the speed control and see if the motor runs, as the poster on dutchforce suggested.

[Stephen Tashiro]

I verified that the speed control can be bypassed by jumpering together two metal female connectors on the assembly that plugs into it. The motor runs when this is done. But the motor also runs when I undo the bypass and reconnect the speed control. Darn!

The speed control module has a copper colored bottom and I think I see heat sink grease inside the module. So perhaps it quits working when it gets hot. I suppose I'll have to contrive a way to run the motor "under load" for awhile.

There is quite a diversity of opinion on the web about this particular model of belt sander. Perhaps the praise vs condemnation is due to to fact that there is poor quality control in the speed control module. It would make me happiest, if I could find a replacement for the module with a different brand of part whose properties are documented. Is there some brand that is known to be top notch? I would be happy to modify and re-do all the all the connections if I could find a quality part.

[Stephen Tashiro]

I finally returned to testing this belt sander. I drilled a 1/8 inch diameter hole in the side of the metal body so I could put a temperature probe from my Fluke multimeter on the speed control module. I ran the sander at speed setting '1' with and 80 grit belt and sanded some pine lumber. The sander got hot and quit working after about 20 minutes. I measured the temperature of the speed control module and it was 111 F. After cooling down for an hour, the sander ran again. Since there is only a DeWalt part number associated to the module, you can't look up the electrical data sheet for it as you can with parts in a normal electronic device. So I don't know if the module is supposed to continue to work at that temperature or whether it is not supposed to get that hot.

Most of the heat is coming from that module, not from the motor or the sanding rollers. Now what should I do - install a fan to cool the module !?