Control Board Circuit Description (Non-Programmable Versions Only) - TTI TSX Series Service Manual

(non-programmable versions only)
The control pcb contains the voltage and current measurement system, the display, the controls
for adjustment of the output voltage, current limit and over voltage protection, plus the output
on/off switch connection. The pcb is connected to the main pcb by a 34-way flat cable. The
control board also contains three preset adjustments.
The measurement system and display are controlled by a microcontroller IC1.
The measurement of output and preset values of voltage, current and OVP is performed by the
12 bit analog to digital converter IC2. The measurement rate is controlled by the 4.0MHz ceramic
resonator XL1 connected between pins 22 and 23 and the buffered version of this 4MHz signal at
pin 25 is used as the clock to the microcontroller IC1. The ADC, IC2, is a dual slope converter
and provides just over 8 readings per second when clocked at 4MHz. The ADC is run in
continuous mode and the status signal on pin 2 is read by the microcontroller every 6ms. When a
reading is ready the microcontroller reads the 12 bit binary value and then converts it to 7
segment BCD and stores it ready to be sent to the display. After each reading the microcontroller
switches the input multiplexers IC3 and IC4 to the next required input. In this way it is possible to
read and display any of the following:
Preset Volts
Preset Current
OVP
Output Volts
Output Current
The multiplexers are controlled by the latch, IC6, which also drives the additional indicator LEDs,
this latch is driven by the microcontroller. The decision on what to measure and display at any
time is taken by the microcontroller and in order to do this correctly a number of status signals
and switches are monitored on a regular basis. These are:
VLIMD
ILIMD
TRIPPED
PRKEY
OVPKEY
DAMPING
OPON
all these signals may be read by the microcontroller as required.
The +2.45V reference line VREF+ is derived from reference diode D35 on the main PCB,
attenuated to about 188 mV by divider R206,207 and then connected to the control board as
ADREF via PJ1-17. It is then applied to the reference input of analogue to digital converter IC2,
yielding a sensitivity of about 92 uV per digit.
The set current signal ISET is taken from the VR4 wiper to feed the current control amplifier on
the main PCB via PJ1-20; it is also fed to the ADC system via adjustable attenuating chain
VR7,R34-36 for display of preset voltage level.
The voltage control signal VSET is derived from the wipers of the coarse and fine voltage controls
VR1 and VR2 via weighting network R19,20 to feed the voltage control amplifier on the main PCB
via PJ1-19; it is also fed to the ADC input via adjustable attenuating chain VR6,R26,28,33 for
display of preset voltage level.
Control Board Circuit Description
from the main board
from the main board
from the main board
the preset key signal
the OVP key signal
the DMPGKEY signal
the output on/off switch signal
11