Service manual

Theory of Operation

DCB, DCFCB and DCFCTB Models

The unit contains an eight-position dipswitch for setting the unit’s site address.

Remote Activation, Sensor and Battery Back-up Voltage Input Section

The remote activation inputs are available on connector JP10. Grounding any one of

these pins activates the function associated with it. The inputs are protected by

limiting diodes and optical-isolator IC U21. There is also a push-button on the board

for each of these functions that activate the associated input.

The Sensor inputs are available on connectors JP10 and JP5.

Rotation, Intrusion, Pressure, Current, and Spare sensor inputs #1 and #2 are all

active low (shorting to isolated ground). When one of these inputs is shorted to

isolated ground the output of the associated optical-isolator pulls low. This is read by

the processor. The 12 Volt, and 48 Volt sensor inputs are analog voltages that are

buffered by U9 and then passed on the A to D convertors in the processor to be read.

These are not optically isolated and are referenced to ground.

For an External Transceiver

The receive audio, from P1 pin 2 (the two-way connector) is routed to U3A the

output of which is set to 1 V

p-p

at TP8 using R48. The CTCSS decoder option, if

installed, gates Q5 on and allows audio to pass. U3B forms a highpass filter. This

strips out any audio frequencies below 300 hertz. This filtered audio is then fed to the

various decoders.

For an Onboard One-Way Receiver

The receive audio enters the through R23 and C9 to Carrier Detect Gate Q2. The

CTCSS decoder option, if installed, gates Q5 on and allows audio to pass. U3B forms

a highpass filter. This strips out any audio frequencies below 300 hertz. This filtered

audio is then fed to the various decoders.

Receiver Priority

Jumper JP4 sets the priority if an external transceiver and an on-board receiver are

both used. The receiver with priority can interrupt the other receiver and its audio

passes through to the rest of the circuits in the controller. The receiver with priority

cannot be interrupted. If neither receiver is given priority then whichever receiver

asserts carrier detect first will pass through and the other receiver will not be able to

interrupt it.

If the "EXT" side is jumpered then the external transceiver has priority. When it

asserts carrier detect the low passes through D3 and R10 turning on Q4. This allows

the received audio to pass through Q4, C8 and R39 to the decoder circuits. The low

also passes through R4 to Q1 which forces Q2 off preventing audio from the

on-board receiver from coming through.