Service manual

Revision D 4-15
Troubleshooting : Control PCB Theory
Series 2000 Treadmill
409110-004
Analog Outputs
Two analog outputs are derived from the two PWM (pulse-width
modulation) output channels. The 8-bit register for the PWM pulses are
used to control an analog switch which provides precise 1.235 V pulses
to an integrator. The output of the integrator is buffered through two op
amps (gain=4.17 ±2%).
Output voltage = (PWM-value) * 1.235 * 4.17 / 255
PWM Output
0 0.000 V ±20mV typical unadjusted offset
1 0.02020 V ~20mV resolution
255 5.15 V ±2% typical unadjusted gain error
These outputs are used to provide two treadmill analog outputs:
GRADE at 1 volt per 5% grade and SPEED at 1 volt per 5 MPH.
Analog Supplies
The +16.5 V and –7.5 V supplies for the analog output and RS-232
circuitry are supplied by the +5 V supply. Capacitor voltage doublers
and inverters are used to get these unregulated supplies from the
LT1133 and the 7660.
Supplies
The EMI filter inductor normally has about a 100 to 200 mV voltage drop
across it (load dependent). +5 VREF is typically at about 5.1 VDC. The
+5V supply is typically at about 4.9 to 5.0 VDC.
ESD and EMI
Compatibility
The one and only connector on this PCB has current limiting resistors
and filtering capacitors on almost every signal to prevent EMI from
escaping this board. These components also limit rise-time and voltages
which may come from ESD or other noise sources.
NOTE
These outputs are accessed through the
SERVICE connector and are referenced to
DIGITAL ground which is NOT connected to
CHASSIS ground. Analog isolation
amplifiers may be required to protect
externally connected equipment.