Sony DNW-A75 Maintenance Manual page 235

(4) RF System (EQ-75 Board and Drum Assembly)
Recording system
The sent REC data from the DPR-118 board is sent from the REC driver on the EQ-75 board to the upper
drum assembly (DR-373 board) as a recording signal through a rotary transformer.
Each channel (A and B) of the recording signal is sent to each REC head through each REC amplifier
with the data records on the tape.
Playback system
The PB RF output signal of each PB head in the upper drum assembly is sent to each PB amplifier in the
upper drum assembly. Only the PB amplifier output signal of the head that is enabled by a head control
timing signal is sent to the EQ-75 board through the rotary transformer.
For the analog Betacam PB operation, RF signals (Y-A, Y-B, C-A, and C-B) are sent to the EQ-75 board
and sent through the equalize block to the DM-89 board.
For the Betacam SX PB operation, a maximum of four-line RF signals are sent to the EQ-75 board. These
RF signals are passed through the amplifier and equalization circuit in the equalize block and converted
from analog to digital. The converted signals are then sent to the inner ECC decode block as PB data. In
the inner ECC decode block, viterbi decoding and inner error correction are performed.
The PB data after error correction is sent to the DPR-118 board.
Control system
The control signal of each head (REC, PB, or erase head) in the drum assembly is encoded to MPX data
by the MPX encoder on the EQ-75 board and sent through the rotary transformer to the upper drum
assembly. The MPX data is decoded to a head control timing signal by the MPX decoder in the upper
drum assembly. Each head is controlled by the head control timing signal.
(5) Analog Betacam PB Video System (DM-89, TBC-23A, and TBC-24 Boards)
The RF signals (Y and C) sent from the equalize block on the EQ-75 board are passed through the COS
equalization circuit for FM demodulation. The demodulated signals are passed through the nonlinear de-
emphasis processing circuit and noise canceller circuit, and the signals are sent to the TBC-24 board.
Additionally, the DM-89 board detects a drop out. A C RF signal contains the analog Betacam PB audio
signal and the AFM signal for CH3 and CH4. The AFM signal is sent from the DM-89 board to the AU-
260 board.
The FM-demodulated video signal on the DM-89 board is converted from analog to digital on the TBC-
24 board and delay-processed for timing adjustment. The resultant signal is sent to the TBC-23A board.
On the TBC-24 board, a sync signal is extracted from a video signal, and memory (TBC-23A board)
control clocks and timing pulses are generated based on the sync signal. The TBC-24 board also corrects
an impact error.
By the video data processing block and line memory, the video signal data sent to the TBC-23A board
performs time-base correction, search picture processing, and CTDM expansion according to each timing
pulse generated on the TBC-24 board.
The Y and C (R-Y/B-Y) signal data read from the line memory is dropout-compensated by the DOC
block and noise-reduced by an ENR block. Moreover, the R-Y/B-Y signal data is LCC (line crawl
cancel)-processed and sent to the MPX block.
The Y, R-Y, and B-Y signals input to the MPX block are converted into a D1 format. The converted
signals are then passed through a setup remove block and sent to the VPR-47 board as an analog Betacam
PB video signal.
In the setup remove block, setup level is removed for an NTSC system (525/60 mode) only.
C-5
DNW-A75/A75P