DSP222H_Manual_A
Page 7 of 17
Apply 24 ±1 volt power to the unit. Connect a loop test box with an inductance of
approximately 115 microhenries to the loop inputs pins D and E (channel 1) and pins J
and K (channel 2) to simulate the connection of loops.
NOTE: All of the following signal measurements are referenced to logic ground.
a) Unregulated power supply.
Voltage across capacitor C16 should be 24 ±1 volt. This voltage can also be measured
at the input of regulator U3 and/or U2.
Possible component faults are diode D6 or resistor R36.
b) Regulated 12 volt power supply.
Voltage at output of U3 (across capacitors C17) should be 12 ± .2 volts. Possible
component fault is the voltage regulator U3.
c) Regulated 5 volt (logic) power supply.
Voltage at output of U2 should be 5 ± .2 volts.
Possible component fault is the voltage regulator U2.
d) Regulated 5 volt (oscillator) power supply.
Voltage at output of U4 should be 5 ± 0.2 volts.
Possible component fault is the voltage regulator U4.
e) Microcontroller clock
Waveform at pin 10 of U1 should be a sine wave at 20 MHz with a peak to peak voltage
of 1 to 2 volts. Note: This value will vary with the type of oscilloscope probe used. The
value stated here is obtained using a Tektronix scope probe with a capacitance of 20
pF.
