Sony UP-21MD Service Manual page 58

(7) AGC (Automatic Gain Control) circuit
This unit mounts a peak AGC circuit that has actual results on the medical market.
The peak value of the RGB signal output from IC204 is sampled by Q301, Q302, and Q303. The
resultant signal is passed through a low-pass filter (R314 and C306) and then input to the operational
amplifier (C302). The control level is properly adjusted by IC302. The input signal is then passed
through a switch (IC307) for manual gain adjustment (output signal at pin 3 of 1C303) and input to the
control pin of GCA (Gain Control Amplifier) (IC304 to IC306).
Fig. 1-7 AGC Circuit
(8) EVR (electronic volume) adjustment circuit
Adjustment is partially performed using an electronic volume by IC303.
1C303 has a five-channel internal DA converter. The four channels of it are used for "VBS gain",
"offset", "AGC gain", and "manual gain", respectively. Adjustment is performed by PCBUS.
(9) EEPROM
EEPROM (IC301) is mounted to store the setting and adjustment values of this board. This EEPROM
writes or reads data by PCBUS.
4-20 UP-21MD V1