Heater board troubleshooting

1
Heater board troubleshooting

• Measurement adjustment of heater board
  parameters
• MJC 2010.05.13

2
Heater voltages

• 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
• 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)
3
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

4
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

5
Troubleshooting heater power failure

1. Base of the large transistor 2N3055 (point 1)
   should be at 12V referenced to the black pin of
   the heater plug
2. 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
3. The base of transistor Q1 (central pin, point 3
   on photo) should be at 5V referenced to TP-GND

1
2

1. 5V regulator at point 4 should be at 5V ref. to
   TP-GND
2. Circuit 5V at point 5 should be at 5V ref. to the
   black pin of the heater plug

3
5
4
6
Verifying potentiometer board power

• The pot board should have 5V over the test points