British Telecommunications (BT) MINIMASTER 1, Manual Notes, Page: 15 / 18

5. MAINTENANCE
Maintenance of the Minimaster
1
is limited to functional testing, replacement of
the power unit fuse or changeout of the CCU, maintenance of the extension telephones
being the same as for standard instruments.
When a Minimaster 1 is reported "out-of-order" the customer should be asked to
switch the power supply off for approximately
10
seconds and to check the operation
of the system when the supply is reconnected. Every attempt should be made to ensure
that the customer is aware of the facilities of the system and that fault reports are not
due to m isoperation.
The CCU comprises a Principal Circuit Board, an Expansion Board and a power
supply transformer.
The Principal Circuit Board comprises the microprocessor, power and tone supplies,
termination and switching matrix for a system of 1 exchange I ine and 3 extensions.
It is mounted on four plastic clips, one at each corner.
The expansion circuit board extends the system to a
1
+
6
by adding the terminations
and switching matrix for 3 more extensions. It is mounted on 4 insulated pillars fixed to the
principal board and is connected to the principal circuit board by means of a plug ended
ribbon cable.
All line terminal blocks are connected to their respective circuit boards as "push on"
connexions to printed circuit board pins. The blocks may be prised off the circuit boards
to save disconnecting the line and extension terminations when changing circuit boards.
The power supply must be switched off before the fuse is removed or replaced and
before the cir
c
uit boards are changed.
Switch SW1 on the expansion board should be set with the "normal" contact
closed and the "door" contacts open. These contacts and links
LKA - LKF
relate to facilities
not offered by the BT Systems.
When a CCU is changed particular care must be exercised to ensure that all configura­
tion switches are set in the same way as those on the recovered unit. This is important as
it ensures that all facilities remain unaffected.
The Minimaster 1 contains a non-divided transmission bridge and consequently
problems may be encountered due to parallel working of extension. These problems are
likely to occur if there is a mixture of dial telephones with carbon microphones
(
Transmitter
16A)
and line powered press button telephones or telephones with microphones
21A
fitted. If problems do arise then all telephones should be changed to high impedance types
with microphones 21
A.
11.