TTI PL Series Service Manual page 3

A damping switch is incorporated on the current meter. This provides a long time constant which
averages out rapidly fluctuating load currents.
The input to the voltage control circuit and voltage meter are brought out to the front panel
terminals labelled 'sense'. These are normally connected to the output terminals by shorting
bars, but can be connected to the output at the load via separate leads in order to eliminate
inaccuracies caused by lead resistances.
Quad Mode Dual (QMD) versions incorporate push button switches enabling Isolated, Parallel,
Series, or Series Tracking operations to be selected. Quad Mode Triple (QMT) units are the
same as the QMD supplies but have an additional higher current 5V output intended for powering
logic circuits. The current rating and sophistication of the logic output varies according to the
model from 5 Volt fixed at 1.5 Amp maximum to 4-6 Volt variable with a 0.1 - 7 Amp variable
current limit.
General and Safety
This manual has been prepared to aid the experienced engineer in the maintenance and repair of
PL Series power supplies. It should be used in conjunction with the owner's instruction manual.
Recalibration or repair should only be attempted by skilled personnel in conjunction with high
quality test equipment. If the user is in any doubt as to his competence to carry out the work, the
supply should be returned to the manufacturer or their agent overseas for the work to be carried
out.
When the power supply is connected to the AC line, terminals may be live, and the opening of
covers or removal of parts (except those to which access can be gained by hand) is likely to
expose live parts.
The supply shall be disconnected from all voltages sources before it is opened for any
adjustment, replacement, maintenance or repair. Capacitors inside the supply may still be
charged even if the supply has been disconnected from all voltage sources. Any adjustment,
maintenance or repair of the opened supply under voltage shall be avoided as far as possible
and, if inevitable, shall only be carried out by a skilled person who is aware of the hazard
involved.
Dismantling the Equipment
The cover is removed by removing the two screws through the handle, and the remaining screws
on each side and on the top.
The front panel may be disconnected from the chassis by removing the two front feet and the
self-tapping screws directly between them. This allows the front panel to be laid forward giving
improved access to the rear of the PCB. All preset adjustments are accessible through the PCB.
Should it be necessary to gain access to the front of the PCB, press in the retaining barb on each
corner fixing pillar and lift off the pcb, having first removed the 3 control knobs.
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