I think you want a manual not a schematic. :-)
Force is usually controlled mechanically.
You should try the Sear's Web site and see if you can find a
downloadable owners or installation or repair manual there.
I don't have a copy of the schematic for your unit, but I do have one
for the 139.53200 Craftsman openers I installed in our home about 20
From what I can see, the "up force" and "down force" controls are
potentiometers used as rheostats to set the dc current fed into two pins
of a control IC.
There is also a photoelectric motor shaft "RPM Sensor" which feeds
pulses into another pin on the same IC.
The IC has two outputs which (through transistor buffering) energize the
coils of two relays (UP and DOWN). Normally open contacts on those
relays applies line voltage across one of two separate windings in the
drive motor. The "other" motor winding gets a phase shifted voltage fed
to it through a single capacitor connected between the "hot" ends of the
two windings. The other ends of the windings are both tied to neutral.
There's a third output from the IC which drives a relay controlling the
light bulb on the front of the opener.
The IC also has a pair of inputs for the "up limit" and "down limit"
switches and a "Command" input from the radio receiver. There's also a
"clock" input which gets a low voltage 60 Hz signal fed to it.
So, I'll make an informed guess that the "force" adjustments control how
much the motor speed is allowed to slow down before the IC decides it's
time to call it quits and unpowers a relay to remove power from the motor.
thanks a lot for your explanation that makes much sense for me. I have
bought my opener in the U.S. but i use it in France, on 120 V 50 Hz and
I had to turn the force controls all the way up for it to operate. I
was suspecting it had to do with some kind of speed sensing, and i was
about to fall short of force. If I could find the schematic, I could
tune up the resistors so that the force detection circuit matches the
reduced speed at 50 Hz.
I innocently did this for 15 years ago I did the same with a 60 Hz
opener (a Genie with a lead screw) and it worked perftectly until it
died a few weeks ago. But the force sensing at that time was an
adjustable friction clutch, so no problem with the frequency.
Jeff Wisnia wrote:
Well, the schematic to mine is in the Sears Owners Manual, but I've no
idea whether they still put them in those manuals.
Per www.sears.com the manual number for your opener is 114A2843.
Good luck "reverse engineering" your unit. From what I recall seeing in
the manual for my unit last nite the two rheostat connected force
potentiometers had their hot ends fed from a +8 volt dc source through a
single series resistor.
If you unit is anything like mine and uses an unpotted PC board, it
shouldn't take the CIA to trace out the circuits around those pots,
measure the voltage at their (common) hot ends and try putting some ohms
in parallel with that series feed resistor I mentioned above.
Good luck, nothing succeeds like success!
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