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? 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.

John

"jbclem" wrote in message
...
| 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? 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.

An AC/DC motor can be reversed by reversing the current flow to the armature
OR the field but not both (since it IS an AC motor).

N

On Thu, 6 Jan 2005 17:36:18 -0800, "jbclem" 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/PorterC...es/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

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" wrote in message
...
On Thu, 6 Jan 2005 17:36:18 -0800, "jbclem" 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/PorterC...es/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