Circuit Description - TC Electronic G-Force Service Manual

Circuit Description

The G-Force consist of a front, a digital, an analog and a power supply section. Here is a brief description of the sections:
Front section consist of three boards and a display, all placed in the front profile. The
big board has two matrix circuits; one for LED's and one for keys. The two encoders
and the two pots are scanned by the PAL. The EEPROM contains the serial no.
The small boards are for LED's and key switches.
Digital section is placed mainly in the middle and in the left side of the main board.
This section contains the Reset, MPU, SRAM, DSP, DARC, Sound RAM, PLL, FLASH
and Interfaces.
Reset controls the MPU the DA.
The Software for MPU is placed in FLASH. The MPU controls DSP, SRAM, Jeida, Front,
MIDI, External Contrl In and analog gain settings.
The major task for DSP is to "calculate" sound. It also generates the 80MHz clock for the
DARC chip.
The DARC chip controls sound data to and from; DSP, Sound RAM, digital in/outputs and
AD/DA converters.
The PLL circuit makes a very stable frequency at 256 x sample rate , this frequency is
divided down to 64 x sample rate and to 1 x sample rate by the DARC. The PLL has its own
power regulation. In newer units the PLL circuit is mounted on a separate PCB.
Interface for MIDI and External Control In consist almost of discrete components.
Interface for Jeida is simplified by using a PAL.
The interface for the front has an integrator, which converts a 3.3kHz square wave to a
negative DC voltage for the display contrast. By changing the duty cycle of the square
wave the DC voltage and thereby contrast will also change. An attenuator allows the MPU
to measure the contrast voltage.
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TC Electronic A/S
Analog section is placed mainly on the right side of the main board.
The analog input is balanced, thus pin 3 should be connected to pin 1 when used with
unbalanced equipment.
Input levels are controlled by digital potentiometers. These potentiometers are located in a
single chip, which controls both the two analog input levels and the two analog output levels.
The A/D converter is a 24bit converter . The A/D and D/A converters have also a separate
power regulation.
The D/A converter is also 24bit. A DC voltage is applied to the left & right signal output at
the converter.
After the D/A comes a 2nd. order filter, then the output level and then a 1st. order filter.
An electronic balanced circuit perform the output stage. Again XLR pin 3 should be
connected to pin 1 when used with unbalanced equipment.
Power supply section consist of a separate Power Supply Module and some regulation
circuits on the main board.
One regulation circuit has an electronic switch for the +/-15V. The electronic switch for the
+5V is mounted inside the Power Supply Module. The switches are controlled by the Stand
By circuit. The Stand By circuit is supplied from a separate power wire from the Power Supply
Module.
This service manual does not contain schematics for the Power Supply Module, because any
attempt to repair the module must be completed with some safety tests such as high voltage
and EMC test. Hence it is strongly recommended that the entire Power Supply Module is
replaced in case of malfunction.
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G-Force Service manual page 12