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Auto Azimuth circuit in 1000ZXL

N.B. The schematic refers to “A3” on several lines. This is a Japanese translation error. The schematic should read “Az” or azimuth.

The Az enable line goes high to start the sequence which turns on the 400Hz oscillator and begins recording. The playback signal feeds the non-inverting inputs of the two halves of IC510. These op amps are set at extremely high gain and convert the sine wave signal into a square wave. That signal is then fed through the two halves of IC511 which serves as a buffer for one channel and inverter and buffer for the other. The result is left and right channel out of phase square waves at the outputs of IC511 – pins 1 and 7. These signals are rectified through D542 and D543 and fed to both the flip flop (½ IC512) as clock and reset respectively and the two three input and gates (IC514). If the two channels are perfectly in phase – that is the azimuth is perfect – then the two and gates of IC514 will never output a high signal since as one channel goes high the other is going low. If the channels are out of phase slightly, one channel square wave will go high before the other channel goes low creating two out of three highs at both and gates. The third input is connected to the flip flop which is timed from the clock and reset inputs. Depending on which channel is leading, the flip flop will be high on either Q or Q (the inverse of Q) creating the third high state at the and gate and triggering its output high. These and gate outputs are connected to the inverting and non inverting inputs of op amp IC513. Depending on which swings high, the output of the op amp at pin 1 will go either positive or negative driving the output pair Q538 and Q539 and subsequently the azimuth motor. The motor will move forward and backward until near zero state is reached at its output. The feedback from the output transistors through R666 (I always knew this was a devilish circuit) turns Q537 off when it is at or close to zero, allowing C532 to charge from the 12v rail through R663. When the reset of the other flip flop in IC512 (pin 10) becomes high enough, that flip flop is reset and the Az End Signal is triggered telling the processor to move on.

N.B. The azimuth motor **MUST be able to turn at ±1.5v.** If the motor armature is dirty or if the belt is too tight and the motor needs more voltage than that to turn, the voltage at the base of Q537 will never drop low enough to allow C532 to charge and the end signal will never be triggered. Checking the motor motion is as easy as pulling the motor connector and powering it with a AA battery.
autoazimuth.txt · Last modified: 2016/07/11 18:30 (external edit)