Download Heater board troubleshooting

Heater board troubleshooting
Measurement & adjustment of heater
board parameters
MJC 2010.05.13
Heater voltages
• The “heater power” voltage is that across
the black and red pins on the plug
• The LCD readout can be calibrated using
the process described on the following slide
• The “heater power” voltage should be ~10V
with the plug disconnected. If this is not
the case, the board needs troubleshooting
Test point GND
(two options)
• The reference voltage applied at the heater
is not at ground, but rather at a positive
value known as the “Heater Bias”
• The true bias voltage can be measured from
test-point-GND to the black pin of the
heater plug
• The value on the LCD screen can be
calibrated to the measured value using
potentiometer R10
Calibrating heater power voltage
•
•
•
•
•
Turn pot 1 until voltage measured across white pins matches front screen
Turn “Heater Power” pot on front to max (fully CW)
Turn pot 2 until reach 2A on front screen
Repeat step 1
Turn “Heater Power” down as appropriate
2
1
Heater bias is tied to ground
• This indicates a short somewhere in (probably) the
TOF
• Thermocouple wire touching anywhere on the
assembly would induce this problem
• Note that the HB voltage is also applied to the
thermocouple, owing to its placement at the
heater tip
Troubleshooting heater power failure
1.
2.
3.
4.
5.
Base of the large transistor 2N3055
(point 1) should be at 12V referenced
to the black pin of the heater plug
Pin 1 of the optical isolator (6-pin
chip) (point 2 on photo) should be at
5V referenced to TP-GND… when the
heater power switch in on
The base of transistor Q1 (central pin,
point 3 on photo) should be at 5V
referenced to TP-GND
5V regulator at
point 4 should
be at 5V ref. to
TP-GND
Circuit 5V at
point 5 should
be at 5V ref. to
the black pin of
the heater plug
1 2
3
4
5
Verifying potentiometer board power
• The pot board should have 5V over the test points