Tait T830 Series, Service Manual

Page: 125 / 284

Copyright TEL 31/01/96
2.5 Power Supply & Regulator Circuits
Figure 2.5 T836/837 Power Supply & Regulator Block Diagram
The T836 and T837 are designed to operate from a 10.8-16V DC supply, although the
standard test voltage is 13.8V. A 5.3V regulator (IC201) running directly from the 13.8V
rail drives much of the synthesiser circuitry. It is also used as the reference for a DC
amplifier (IC202d, Q209, Q210) which provides a medium current capability 9V supply.
A self-oscillating, switching power supply (Q208, Q212) runs from the 9V supply, pro-
ducing a low current capa20V supply. This is used to supply the synthesiser
loop filter (IC6), giving a VCO control voltage range of up to 20V.
Ultimate control of the transmitter is via the Tx reg. supply, switched from 9V by Q211.
This is enabled by the Tx enable signal from the audio processor, but is subject to gating
by the transmit timer (IC202b). If the transmitter is keyed continuously for a time
exceeding that set by RV201 and C222, the Tx timer will force the Tx reg. supply off until
the transmitter is keyed again. If required, the Tx timer may be disabled by removing
R257.
The tail timer provides a repeater tail of up to several seconds and is adjusted by RV202.
Tx Enable
Buffer
IC202a
Tx Timer
IC202b
Tail Timer
IC202c
Q211
Tx Reg.
+9V
5V
REG
PS
IC201
IC202d
Q209
Q210
DC
Amp.
Switching
Power Supply
Q208
Q212
20V 9V 5V 13.8V
Nominal
13.8V
Nominal