Re: Diagnosing reversing trigger switch on drill

From: jbclem (jbclem1_at_charter.net)
Date: 01/09/05 

Date: Sun, 9 Jan 2005 01:33:29 -0800

Kim,

Thanks for laying it out for me. I actually have the same schematic(s) that you found
at Acetoolrepair, but I hadn't noticed the part that was the reversing switch on top of
the trigger switch, and wouldn't have been too sure which wires to test. I'll test for
continuity, and I expect it'll show what we already suspect...bad switch.

Since this is a borrowed tool I don't have the option of going without reverse, I found
a web site with the switch for $32 and the Sears price will be a good backup.

Regards,

John

"Kim Clay" <kimclay@myrealbox.com> wrote in message
news:j34ut057rvv5taudukq4gsr217snaipm2a@4ax.com...
> On Thu, 6 Jan 2005 17:36:18 -0800, "jbclem" <jbclem1@charter.net> wrote:
>
> >I have a Porter Cable hammer drill (#7750) and the reverse isn't working. I have
opened
> >up the handle and accessed the trigger switch, but there are a few too many wires
going
> >into it for me to figure out where to test. I see the main current wires(one white
and
> >one black) coming into it, and the two wires(one black and one red) going to the two
> >brushes. But I don't understand how the reversing action occurs. Is it a simple
> >reversing of the polarity going to the brushes?
> Yes
> >If so, how to test? Do I have to test
> >it live, or energize the wires with a small battery? I'd like to ask for some ideas
on
> >this.
>
> I went to Google - typed in -
> "Porter Cable" 7750
> & the third result was this page:
> http://www.acetoolrepair.com/PorterCableHTML/7750.htm
> which contains a picture type schematic better viewed as:
> http://www.acetoolrepair.com/PorterCableImages/7750pg2.gif
>
> The above gif has two versions with the reversing switch wired the same
> in both. From the drawing reversing is done on the armature leads (the
> black & red leads to the brushes).
>
> The reversing switch is the rectangle on top of the switch - with the
> armature connected to the "A" & "D" terminals.
>
> In one direction:
> "A" connects to "B" and "D" connects to "C"
> In the other direction:
> "A" connects to "C" and "D" connects to "B"
>
> If you want to test it independently then disconnect the wires & test
> with any continuity tester. Test for continuity between terminals
> mentioned above. One set of contacts will be open if it is defective.
>
> From your description the trouble is almost certainly in the reversing
> switch. If the drill runs in one direction & not the other the trouble
> must be in this switch. Maybe something you can see is preventing full
> movement of the reversing switch lever? A replacement may be
> available.....
> Hmmm... Looking at the exploded diagram the switch/triac is item #4 &
> the parts list shows it as "switch/triac" assembly. It seems the switch
> assembly is not available separately. Also two different styles of
> switch/triac assemblies were shipped for this model & only the later
> design is available as a replacement (per drawing note).
>
> A hammer drill puts _lots_ of extra stress on the whole switch
> assembly/wiring & can vibrate internal parts enough to break. As these
> switches are usually sealed replacement is required.
>
> The "switch/triac" part number seems to be 873498. Going to Sears parts
> http://www3.sears.com/ & inputting this p/n it seems they have it for
> $41.75. It is described as a "Switch".
>
> Or just don't use reverse :)
>
> No guarantees - Double check everything I say - Please be safe!
>
> Kim
>

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