General - TTI QPX1200 Service Manual

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
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 1500VA.
High voltages (up to 400V) are always present in the primary-side circuits on both the PFC board
and Power board; on the Power board the primary side occupies a clearly defined area at the rear
of the board.
1. Remove the 4 side screws to release the top cover.
2. To gain access to the Control PCB and Keyboard, release the front panel assembly from the
chassis by removing the 2 M3 side nuts, the countersunk M3 screw securing the top bracket,
and the 4 M3 screws (with integral shakeproof washers) along the bottom edge.
3. Keyboard: Remove the 5V supply from PJ4, the 4 connections to the mains switch, and the
3-way connections to the Control (PJ10) & Interface (PJ9) boards. The Keyboard is released
from the front panel by removing the 7 screws which secure it.
4. Control: Remove the 10-way connector (PJ100) to the Power board, noting polarity (corner
marker to pin1); remove the flat cable connection to PJ101 and the 3-way connection to the
Keyboard (PJ105). Remove the nuts which secure the front and rear output connecting
cables from the terminals on the front panel/Control board after noting their positions. To
release the Control board remove the 3 M3 screws to the front panel plus the 3 nuts which
secure it directly to the +, −, & earth terminals. When re-assembling do not forget the brass
bus-bar between the Red output terminal and the current measurement shunt connection.
5. PFC: Remove the 5V supply to the Keyboard (at PJ2) and the mains connections at W1,
W2, W3 &W4; when reassembling note that W1 & W4 (to the front panel switch) share a
ferrite sleeve and W2 & W3 (return from the switch) share a ferrite sleeve. Remove the 4-
way primary AUX connection at PJ1 ( note the position of ferrite sleeve at the Power board
end of the connection) and the HT connection at FAS5, FAS6 & W5. To release the PFC
board from the chassis remove the 9 M3 screws (with integral shakeproof washer) from the
underside of the chassis, leaving the support pillars attached to the board assembly. Ease
the board forward a little in the chassis, so that the safety earth connection to the rear panel
can be undone, and lift the board free.
WARNING!

General

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