Teledyne 9110TH - Nitrogen Oxides Analyzer - Manual (Page 271)

Troubleshooting & Repair Model 9110TH NOx Analyzer
Teledyne Analytical Instruments 251
9. Discard the plastic screws and replace with new screws at the end of this procedure
(the threads get stripped easily and it is recommended to use new screws).
a) Carefully remove the assembly consisting of the HVPS, the gasket and the PMT.
Both may be coated with a white, thermal conducting paste.
b) Do not contaminate the inside of the housing with this grease, as it may
contaminate the PMT glass tube on re-assembly.
10. Change the PMT or the HVPS or both, clean the PMT glass tube with a clean, anti-
static wipe and do not touch it after cleaning.
11. If the cold block or TEC is to be changed:
1. Disconnect the TEC driver board from the preamplifier board, remove the cooler
fan duct (4 screws on its side) including the driver board.
2. Disconnect the driver board from the TEC and set the sub-assembly aside.
12. Remove the end plate with the cooling fins (4 screws) and slide out the PMT cold
block assembly, which contains the TEC.
13. Unscrew the TEC from the cooling fins and the cold block and replace it with a new
unit.
14. Re-assemble this TEC subassembly in reverse order.
Make sure to use thermal grease between TEC and cooling fins as well as between
TEC and cold block and that the side opening in the cold block will face the reaction
cell when assembled.
15. Evenly tighten the long mounting screws for good thermal conductivity.
Note The thermo-electric cooler needs to be mounted flat to the heat sink. If
there is any significant gap, the TEC might burn out. Make sure to
apply the thermal pads before mounting it and tighten the screws
evenly and cross-wise..
16. Re-insert the TEC subassembly in reverse order.
Make sure that the O-ring is placed properly and the assembly is tightened evenly.
17. Re-insert the PMT/HVPS subassembly in reverse order and don’t forget the gasket
between HVPS and PMT.
a) Use new plastic screws to mount the PMT assembly on the PMT cold block.
b) Improperly placed O-rings will cause leaks, which – in turn – cause moisture to
condense on the inside of the cooler and likely cause a short in the HVPS.
18. Reconnect the cables and the reaction cell (evenly tighten these screws).
19. Replace the sensor assembly into the chassis and fasten with four screws and
washers.
20. Reconnect all electrical and pneumatic connections.
21. Leak check the system.
22. Power up the analyzer.
23. Verify the basic operation of the analyzer using the ETEST and OTEST features or
zero and span gases, then carry out a hardware calibration of the analyzer
(Section 13) followed by a software calibration.