SCP SCIENCE DigiPREP, Service Manual

Page: 30 / 88

SCP SCIENCE
30
KeyPad
Version 1.0
Q2 SWITCH (NPN BIPOLAR TRANSISTOR)
VERIFICATION
• If the signal on TP8 coming from the CPU is
on, the problem could be the bipolar
transistor Q2.
•Measure with a multimeter the voltage
between Q2 collector pin 3 and GND. If the
signal on TP8 is pulsing, Q2 should switch
between 0.3V and a maximum of 4.7V. If
TP8 is high, Q2 should be steady at 0.3V. If
Q2 is OK in either case, the problem is
probably the triac (see below)
• If the signal on TP8 is low and the LED is ON,
then Q2 is defective.
D9 LED verifi cation
If Q2 is good and the signal on TP8 is high or
pulsing and the LED lights up or pulsing, the
LED is OK. If not, D9 is defective.
TRIAC T1 verifi cation
•
The only way to see if the Triac is behaving
correctly is by measuring between " HEATER
connector" pin and "NEUTRAL" ( see fi gure
19). Make sure that there is 120V/230V AC
(toggling or not). Also refer to fi gure 20 for
an example of what an be seen on a scope if
the control is toggling.
• Make sure that the heating block
temperature is lower than the set point
temperature if you want the Triac to toggle.
• If the triac output remains low while it should
toggle as shown in fi gure 20, replace the
triac.
If you're using a scope, it must be
isolated from the wall outlet.
FIGURE 19: HEATER DRIVE TEST PINS AND
COMPONENTS LOCATION
Legend
1. Q2 pin 3 (collector)
2. HEATER pin (Hot)
3. NEUTRAL pin
4. T1, Triac
FIGURE 20: TRIAC OUTPUT WHEN HEATING
SECTION IS FIRING
If all of those tests are correct, please
refer to the Digi
PREP
block service
page 62 for more details.
A/D CONVERTER
The analog to Digi tal conversion is the feed back
information coming from the block temperature
sensor or from a
Digi
PROBE
. The CPU section
handles this information in order to monitor and con-
trol the block temperature.
NOTE