MODULE Replacement CMU
1100.4903.82 3.50 E-4
Replacing the Instrument Fan
(see chapter 5, spare part list, Current No. 80, and explosion drawing 1100.0008.01 D sheet 2)
The fan is fitted at the right side panel of the CMU in an air duct. For replacement proceed as follows:
Opening the instrument and removing the fan
½ Switch off the instrument, pull the mains plug and unscrew the rear-panel feet.
½ Place the instrument onto the front carrying handles, push the tube upwards and take off.
½ Place the instrument onto the left side and locate the fan connecting cable. Coming from the air duct,
the cable leads to connector X211 at MOTHERBOARD1 near the Option OCXO REFERENCE
OSC.. If this is installed, it can as well be removed in order to enable easier access to the fan
connector (see replacing the OPTION OCXO REFERENCE OSC.).
½ Pull off the connector from MOTHERBOARD1. To this end, press the locking lever at the top of the
connector towards the connector and lift off the cable.
½ Lever off the cover of the air duct and unscrew the four countersunk screws of the fan in the right
side panel of the CMU. Carefully take out the fan towards the top and pull the connecting cable
through the hole in the air duct (Take off the adhesive tapes of the cable entry and keep them for
later).
Installing the new fan and completing the instrument
½ Replace the new fan in the reverse order.
Note: Make sure that the air direction of the fan is such that air is sucked in from the right side of
the CMU and pressed through the air duct. Note the arrows on the fan casing.
½ Reconnect the fan connecting cable to MOTHERBOARD1 (Fix again the adhesive tapes of the cable
entry).
½ Complete the instrument without causing damage to the cables.
½ Connect the instrument to the mains and switch on.
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