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Servicing
SAFETY.
These safety notes are directed to those testing and repairing this power supply.
Legal requirements mean that we must not encourage untrained personnel to
take the lid off.
Servicing should only be carried out by a competent
service engineer.
This supply contains mains voltages on the voltage select PCB, the mains switch,
etc, and the usual precautions must be taken.
The main reservoir capacitors have a capacity of 20,000 uF, and are charged to
+26V.
THIS CAN BE DANGEROUS.
The danger lies not in the voltage, but in the large currents that will flow if the capacitor
terminals are shorted. A small screwdriver will simply disappear in a violent
explosion. The main bodily danger is from metal watchstraps, etc. Serious burns are
very likely if these contact the capacitor.
For safety reasons, the reservoir capacitors are discharged by bleeder resistors at
switchoff; this takes about 10 seconds.
The unregulated supply to the +48V regulator can reach +90V on high mains,
and should be treated with some respect.
Initial operational tests on the power supply can be carried out by switching the unit
ON and checking the voltages present on the output connectors on the back of the unit.
While the unit remains disconnected from the mixing console some of the DC voltage
rails are floating with respect to each other, that is they do not all have a common
reference within the unit. When connection is made to the mixing console various
output pins become earthed to a common star-point, which has a mains earth return
in the power supply cable itself.
An indication of obvious fault condition is the failure of one or more of the front-panel
LED’s to light.
Any fault condition, with the exception of simple mains fuse failure due to underrating
or an unusual mains input condition, will require removal of the top cover to enable
fault correction. This is achieved using a cross-head screwdriver to remove the six
retaining screws and washers. Carefully lift the cover to avoid the earth connecting
lead to the cover from snagging. Place the cover face down behind the unit.
WARNING: At the front of the unit just behind the
front panel is the MAINS SWITCH, which carries
HIGH VOLTAGES directly from the mains input.
Similarly on the rear panel is the MAINS INPUT
SOCKET/MAINS VOLTAGE SELECTOR.
Care MUST be taken when carrying out any
servicing operation with the top cover removed.
Technical Description 17