Brother FAX-615, Руководство по обслуживанию

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3.3 NCU PCB
The NCU PCB switches the communications line to telephone or built-in MODEM, under
control of the main PCB. Also, it works as a power supply interface from the power supply
unit to the main PCB and the recording head.
As shown in the circuit diagrams on the next page, the NCU PCB consists of the compo-
nents listed below:
1
Surge absorber
7
Calling signal detector
2 Noise filter 8 Loop current detector
3 Line relay (CML relay) 9 Dial pulse generator
4 Line transformer : Telephone circuit
5 Circuit related to line transformer a Recording head interface
6 High-impedance transformer circuit
• The primary function of the NCU which is shared by facsimile and telephone units is to
switch a line to the facsimile unit or to the telephone, which is carried out by the line relay.
• Since the direct connection of a facsimile equipment to the line is not allowed for protect-
ing the line, it is essential to insert a line transformer between the line and the facsimile
equipment to insulate them each other in direct current band.
The above two components, a line relay and a line transformer, are the minimum require-
ments for the NCU of the facsimile equipment.
• If an external telephone is attached to the facsimile equipment, the NCU should have a
loop current detector to identify the hook state by detecting loop current.
• If the facsimile equipment has an automatic answering facility, the NCU should be
equipped with a calling signal detector which detects a calling signal and tells it to the
CPU in the FAX engine.
• The circuit related to a line transformer allows the line transformer to be invariant by se-
lecting the constants of the parts in this circuit so as to conform to the communications
regulations or codes of each country.
In addition to the above basic components of the NCU, the following components are also
required depending upon additional functions of the facsimile equipment:
• The dial pulse generator generates dial pulses within the facsimile equipment.
• The surge absorber is a protection circuit which absorbs lightning surge.
• The noise filter eliminates noise including radiation noise to prevent them from flowing out
onto the communications line.
• The high-impedance transformer circuit detects the remote activation, and F/T switching
sent from the line in ON-HOOK state without any interference to the line.
• The telephone circuit includes two amplifiers; one for amplifying the output signals of the
handset microphone and the other for amplifying the receive signals from the communica-
tions lines to sound the handset receiver.