1. Heater board troubleshooting
Measurement & adjustment of heater board parameters
MJC

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 1 2

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
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 1 2
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 3 5 4

6. Verifying potentiometer board power
The pot board should have 5V over the test points