Teledyne GC-Pro/FID - Gas Chromatograph - Manual (Page 104)

Maintenance GC-Pro FID
Teledyne Analytical Instruments 90
Whenever the flame guard and anode power supply printed circuit
board have been replaced the analyzer must be recalibrated.
If the instrument performs as outlined in this section, the problem is
not related to the measuring circuit electronics.
5.1.4 Collector Cable
Before reconnecting the collector cable, check the continuity of the
center wire of the cable with an ohmmeter by measuring between the
center pins at each plug on the lowest resistance scale of the meter. Flex
the cable while making this measurement to be sure that there is not an
intermittent open circuit. If there is, replace the cable. Do not attempt to
repair the cable, as special tooling is required to disassemble and
reassemble the cable plugs.
5.2 Temperature Control Electronic Check
If the heating circuit fails, the output of the analyzer will tend to drift
with changes in ambient temperature. Such a failure will be more
evident in the low range. If the temperature environment surrounding the
analyzer is closely regulated, failure in this circuit might go unnoticed
after the initial failure. If the environment follows day and night
temperature changes, the analyzer will show a diurnal, bi-directional
drift when operated on zero gas. The magnitude of the drift will be a
function of the temperature differential experienced by the analyzer. To
check the circuit, employ the following procedure:
Consult the GC-Pro FID schematic and assembly drawings, as well
as the temperature control PC board schematic and assembly drawings at
the rear of the manual for circuit details and component placement.
An indicator light behind the analyzer door cycles on and off with
the heating element; the light is on when the heater is on, and vice versa.
Failure of the light to come on at all when the cell compartment is cold
indicates a problem in the temperature sensing or control circuitry or the
wiring that interconnects the thermistor to the circuit. If the light stays
on constantly, but the compartment does not heat up, then a problem
with the heating element or connecting wiring is indicated.
1. Check the sensing thermistor by measuring the resistance
between its connecting wires. Disconnect one of the thermistor
wires from terminal strip on the temperature controller board,
P/N B30927, the wires out of the thermistor are yellow, and