Introduction
Anyone with a Precor knows what excellent machines Precor manufacturers.
My Precor has been around the world distance wise, and all that travel
finally took its toll. The user manual states that there are no user
serviceable parts inside. However, from my point of view, I find nothing
but user serviceable parts inside.
If you rebuild automobile engines for pleasure, wouldn’t consider taking
your car in for ‘service’ for any reason, repair all of your household
appliances including HVAC, and deal with fried computers with an
oscilloscope, you may be able to make good headway in repairing these
exercise devices.
Safety
These exercise machines are loaded with potentially lethal high voltage
circuits, delicate logic components, and sharp, massive rotational
structures and lever actions that can snap your fingers off effortlessly
while roasting you with wall current and permanently frying your
electronics. Decide for yourself if your background, experience, and
available tools permit you to work in such environment before venturing
any further.
Disclaimer
I have never worked on a Precor or any other type of exercise device until
now, so do not take any of this article as ‘expert’ or ‘authoritative’
advice or official procedure. It is anything but. This article is a record
of my repair of a rather abused Precor EFX-5.21S for the benefit of
interested, technically qualified parties. Use at your own risk.
Problem Description and Solutions Overview
This article describes three (3) failures clearly attributable to being on
the road too long with my trusty Precor, summarized as follows-
Shipping my Precor across the Pacific (twice) and completely across the
continental USA (twice) and other manhandling finally initiated a failure
that compounded into multiple failures. Specifically, upon reassembly of
the handlebars to the main body and applying power, the unit came up
properly. However, when I patted the handlebars welcoming the machine back
from the road, the incline motor suddenly initialized and began an
uncommanded descent that crashed the assembly before I could unplug
power.
This failure was due to a wire slipping out of a wire nut and lodging into
another, completing the descent AC path (PROBLEM 1). The resultant
over-travel of the uncommanded descent also cracked a drive gear in the
lift-motor transmission case, discovered only later when that gear finally
disintegrated (PROBLEM 2).
In addition, the stresses of shipping the Precor as much as I did finally
worked a ground strap loose, which caused excessive electrical noise
(visible with an oscilloscope) on the logic signals of the LED display
area, rendering the display partially usable. Specifically, the power-on
message banner would transit perhaps half the display length and then
disappear (PROBLEM 3). This failure mode repeated, and manifested itself
after problems 1 and 2 were resolved.
The following photos and diagrams illustrate these failures and their
resolutions.
Figure-1. Precor EFX-5.21S with covers removed.
A well-designed, well-built machine that with covers off is just waiting to
severely pinch, shock, or outright chop your fingers off. As always, restrict
access to your work area and immobilize the mechanicals.
Figure-2. Rear assembly of the EFX-5.21S. Note the scissor
lever action coupled with the heavy rotational mass at right. These normally
shielded parts are designed to be in motion and happily comply at the slightest
provocation. For safety’s sake, jam this mechanism while working with the shields
removed, least you loose your fingers.
Figure-3. PROBLEM 1 resolution: reset the DC sensor and AC
drive wires into their proper arrangement. Here I solder for security and then seal
with heat shrink tubing. The migration of a wire from one wire nut to another is a
rare occurrence, apparently caused in this case by the wire pulling out from its wire
nut when it interacted with the lift gears. I found the wire pulled into the gearbox,
despite an internal metal shield designed to segregate gearing and wiring. This was
thus likely an assembly error on the part of the lift motor manufacturer, aggravated
by shipping stresses.
Figure-4. Soldered control and sensor wires sealed with heat
shrink tubing, shown (obviously) with the protective plastic cap of the motor assembly
removed.
Figure-5. (Future) PROBLEM 2: the red gear shown here in the
exposed lift motor transmission case is cracked from the uncommanded descent described
in the text. I did not see the crack and the gear failed about two years later in normal
use. This is resolved beginning with Figure 7. Take the time to redistribute the grease,
especially when replacing a broken gear. The new gear and its axle must be coated, and
redistribution also helps uncover small fragments of the shattered gear. Be sure to grease
the base of the lift bearing.
Figure-6. Another view of the lift motor transmission case and gear
arrangement. The white gear at left all by itself is connected directly to the potentiometer,
which sends lift-position telemetry to the logic board located in the aft section of the EFX.
That gear is friction-fitted, despite what appears to be a screw attachment. If you replace the
pot (I did, later), get a precision 1K center tap pot. You might have to cut out the black covering
cap a little bit to accomadate larger pots. This is not an issue, with the way the motor sits in
the EFX (plenty of clearance). BTW, if you connect the +5v and GND backwards from the way the EFX
expectes it, it will complain with an Err42 (Error 42). So, don't final solder and shrink tube
the pot connections until the EFX's computer is happy with it. Click here for
Precor Error Codes (PDF).
Figure-7. Shattered drive gear in degreasing fluid.
This is the red gear of Figure 5 which lasted 2 years before disintegrating.
Figure-8. Reassembled gear, suitable for mold-making.
Figure-9. PROBLEM 2 resolution: casting new gears for the
lift-motor transmission case. Mold at top contains rapidly solidifying liquid plastic.
Gear at bottom is of a prior casting. There are few spare parts available for this
machine, so sometimes you have to make your own like this. You could probably use epoxy
resin but that stuff is usually so thick you might need a strong vacuum chamber
to get all the air bubbles out. Either that or be careful pouring the resin.
Figure-10. Empty mold and cast gear. The mold itself was created
from the shattered gear super-glued together to create the master form. Make several
casts for spares and testing.
Figure-11. Very poor close-up of a finished gear cast. The gear
itself is characterized as a helical type (28 teeth) with integrated spur gear
(the smaller toothed crown, with 22 teeth). I drilled the axle hole with a
Drill Press Plus
purchased for this particular job, with an attached Dremel moto-tool.
Figure-12. Replaced gear (near screwdriver tip).
I'm also replacing the original pot (with cut wires, foreground) with a
precision 1K pot (installed, not yet wired) since I had the hood up
on this assembly. The new gear and its receiving axle must be dunked
in grease. Be sure to stress test the gear, minding motor duty cycle
(very short due to operational heating). Example: run motor from level
1 to 7 and then back to 1 again, repeat, and then let motor cool to touch.
Repeat several times, disassemble transmission, and inspect replaced
gear for damage / wear. Note-polarity matters on the pot; reverse polarity if
you get an error code on the EFX's LED display. Motor assembly requires
calibration with lift mechanism during re-installation; run lift motor
to lowest lift level (1) and then spin-on lift T-bar by hand until
contacting motor case, then back off (up) 3 or 4 turns. Reassemble to
EFX frame, along with motor assembly ground strap and test lift for
unrestricted travel within the lift bezel.
Figure-13. PROBLEM 3 resolution: note the unattached, rebuilt
ground strap (at arrow). The original had worked loose its attachment nuts and even the strap
itself from its eyelets. Here I have replaced the original eyelets with new ones
soldered onto the ground strap cable for security and later bolted to the grounding
studs visible here adjacent to the strap. This resolved the display problem and I
was able to remove my custom grounding cable I had attached to the display in an
earlier fix.
Figure-14. The repaired EFX-5.21S ready to go.
Appendix
Lift motor wiring diagrams-
These, like ALL of the information in this article, are unofficial.
Figure 15. Wiring diagram I generated for my particular EFX.
The pot turns about 220 degrees and stops, after which gear motion will result in
gear (and maybe pot) destruction. Lack of changing DC voltage on the pot’s center
tap causes the Precor to shutdown the lift and report an error, a very good design.
Accordingly, running this assembly outside of computer control is guaranteed to
destroy the sensor transmission gears and maybe even the pot itself. You will find
many such motors available for sale on the Internet as ‘new’ or ‘tested, like new’
having this damage.
Figure 16. Cable from EFX frame to motor assembly for my
particular EFX. Shorting the orange or frame ground to the black wire causes the
lift to ascend. Doing likewise to the red wire descends the lift. Use this for
diagnostic measures but mind the connected sensor potentiometer’s limited range
of motion.
Figure 17. Motor connector for my particular EFX.
Mark Qu