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 1 2 • 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 • 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