TTI EX752M, Service Manual

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General
Service Handling Precautions
Service work or calibration should only be carried out by skilled engineers using high quality test
equipment. If the user is in any doubt as to his competence to carry out the work, the instrument
should be returned to the manufacturer or their agent overseas for the work to be carried out.
The tracks on the printed circuit boards are very fine and may lift if subjected to excessive heat.
Use only a miniature temperature-controlled soldering iron and remove all solder with solder wick
or suction before attempting to remove a component.
Dismantling the instrument
WARNING!
Disconnect the power supply from all voltage sources before it is opened for adjustment or repair.
Capacitors inside the supply may still be charged even if the supply has been disconnected from
all voltage sources but will be safely discharged about 10 minutes after removing power.
If any adjustment or repair of the opened supply under voltage is inevitable it shall be carried out
only be a skilled person who is aware of the hazard involved. The incoming AC supply to the unit
under test should be isolated for safety by means of a 1:1 isolation transformer of at least 700VA.
High voltages (up to 400V) are always present in the primary-side circuitry which lies in a clearly
defined area at the rear of the main printed circuit boards.
1. Remove the 6 side screws and front handle screw to release the top cover.
2. Unplug the 3 connector assemblies linking the main pcb to the front panel control pcb,
noting their orientation (brown wire to pin 1 corner marker).
3. Unplug the mains connection at the rear of the pcb and remove the chassis safety earth
connection.
4. Undo the 10 screws which secure the main pcb support pillars to the chassis (i.e. the
screws accessible
underneath the chassis) and lift out the pcb with its mounting pillars
attached.
5. To remove the control pcb on the front panel first remove the main pcb. Pull off the 6
control knobs and the mode knob, then undo the 5 screws which retain the pcb to the
moulding and the 4 nuts which connect the pcb to the output terminals. The control pcb
can then be lifted clear.
6. Reassemble in the reverse order taking great care to ensure that all connections are
exactly as before dismantling and that no insulation creepage and clearance distances
have been compromised. Ensure that only the correct fastenings have been used
otherwise earthing, and hence EMC and safety performance, may be impaired.
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