I have a PC Speed Bloc that was and has worked fine since 1989. Yesterday
while using it the motor sounded like it was slowing down to about half
speed and now runs at that speed always.
Does it sound like a brush problem? I pulled the brushes out and there was
a dull spot on one and the springs seem weak.
This is how I deal with this situation...
YMMV, IMHO, etc.
The brushes are generally designed to be a certain length, and this
combined with spring pressure determines the optimal contact pressure
on the commutator. But this requires knowing the 'new' length as
opposed to the 'now' length. If you can see the brush contact patch
from outside the device, for instance through a vent hole, look for
evidence of excessive sparking/trails. Heat also causes the springs
to lose tension.
You could opt to simply replace them, it's been a while. Clean the
commutator, but don't use emery cloth as is sometimes done. Embedded
particles will cause accelerated erosion of the copper blades. Their
surfaces are turned on a lathe, and the slots between blades are cut,
square bottomed. Keep this in mind when attempting to clean up the
armature. Check the bearings for smooth operation. Check for other
worn parts in need of replacement.
A short term solution, if the brushes are not cracked and burned, is:
First - order 2 new brushes sets and springs (commonly included)
Also order any bearings and misc. parts which seem worn.
Second - stretch the springs to 150% of their original length.
Reinstall and make sure the brushes maintain their original
contact pattern. Use until new brushes arrive and replace.
This is a short term repair at best...
The PC site indicates the brushes are 9/16" new. I'll yank them out and
Bearings seem fine but I'll stretch the springs as they do seem weak. I'll
clean the commutator with electrical cleaner and soft brush.
Thank you Greg. At least this will let me know if it is indeed the brushes.
I did now ever buy a new Speed Bloc Yesterday also. I am in the middle of a
job and could not wait. I'll just have a back up or spare parts if this
Leon (in G_%ff.22733$ firstname.lastname@example.org) said:
| I have a PC Speed Bloc that was and has worked fine since 1989.
| Yesterday while using it the motor sounded like it was slowing down
| to about half speed and now runs at that speed always.
| Does it sound like a brush problem? I pulled the brushes out and
| there was a dull spot on one and the springs seem weak.
Brushes could be a problem; but another possibility is the eccentric
drive. My speed bloc showed similar symptoms ( After only 30 years of
use! They just don't make tools like they usta :-) and my machine's
problem was with the eccentric rather than the motor itself.
I took it in to my local PC service guys this past spring and it cost
$15 to have the old part replaced. The old cord had become brittle and
cracked, so I had that replaced at the same time (for another $15).
Should be good for another 30 years...
DeSoto, Iowa USA
Hi Morris. I suspected something being out of balance as the sander shook
much more than usual. This is not unusual however because it has always
shook during start up and while coasting down to a stop. Even the new one
does this. I did remove the eccentric and the motor still runs slowly. I
had a part of the pad assembly fly apart a couple of years ago and with only
one small part missing the balance was thrown out enough that it shook
violently. I replaced the pad assembly and every thing was fine for 2
years. Greg suggested that excess sparking at the brushes might indicate
bad brushes and I do see what seems to be excess sparking when I had the
eccentric off and the sander was running.
I was shocked how pliable the new cord was on the new unit. LOL
Thanks for the suggestions.
If the bearings are free, I'm guessing you have an open winding in the
armature unless the sander has a defective variable speed switch. You can
check the armature with an ohm meter by connecting each lead of the meter to
each side of the sanders power cord (sander not plugged in). Turn the motor
by hand (be sure sander switch is on), the meter needle/ or reading if a
digital meter should stay constant as you turn the shaft by hand if the
armature is good. If it's bad (dips in readings) you would probably be
better off looking for new sander due to the costs of new armatures. RM~
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