Thermo Scientific SGD-O, User Manual

Page: 45 / 73

Troubleshooting & Service
The FSU Pre-Amp Board
Thermo Fisher Scientific SGD-O User Guide
9-5
If the output voltage is very low and using the R35 pot will only adjust
the output approximately 0.5 to 1.0 Vdc, check the R5 resistor on the
pre-amp board. If it is a 49.9 kohm resistor, replace it with an 8 kohm
resistor. Doing this should raise the gain enough to obtain the 9.6 Vdc
output with air in the pipe. If it does not, it is like the pre-amp requires
repair or replacement.
5. If you suspect the pre-amp board is bad, check the factory settings on
the board. Continue to the next section.
Note
If you purchased a pre-amp board (p/n 885623) by itself as a spare
part, the R1 and R28 pots have not been set. In this case, it is necessary to
follow the procedure in the next section so the pre-amp board will operate
properly.

6. With power applied to the pre-amp board, connect a wire jumper from
the center conductor coaxial cable to test point 6. Measure the voltage
at test point 6 and use the R28 pot to set this voltage to -80 mV.
Measure the Vdc on test point 1 and use the R1 pot to set this voltage
to +5 mV.
This section provides a procedure for troubleshooting the SGD-O FSU
pre-amp board (p/n 885623). The procedure will aid technical personnel in
determining if suspected problems with the pre-amp board are simple
calibration issues that can be resolved with adjustment of the
potentiometers on the board or actual component failures that require the
board be replaced or returned to the factory for repair.
Two Hi-Meg resistors are required. They are listed below with the Thermo
Fisher Scientific part numbers.
●
4.7 x 109 ohm resistor, p/n 351760
●
4.7 x 1010 ohm resistor, p/n 351810
Note
If you purchased a pre-amp board (p/n 885623) by itself as a spare
part, the R1 and R28 pots have not been set. In this case, it is necessary to
follow this procedure so the pre-amp board will operate properly.

The locations of the components and jumpers referenced in this procedure
are shown in Figure 9–2 and Figure 9–3 .
The FSU Pre-
Amp Board