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When an external center channel speaker is connected, the
Scart 3 + VGA-audio module, TA710
link to the switch is disconnected. In this situation, the soft-
ware requests the user to change the switch position.The scart 3 + VGA-audio module makes it possible to have
The left and right channels from the main board are con-not only one extra scart connection, but also one extra
nected to connector Q3, and due to the other switch posi-audio connection (VGA-audio). The audio input is via the
tion, the left and right channel signals are now fed via theVGA-audio connectors, when VGA mode is selected.
switches directly to the internal speakers. This is assum-The characteristics of scart 3 are identical to those of scart
ing, of course, that external left and right speakers are not1.
connected.The RGB switch ica2 selects the signals either from scart 3
or from scart 1. The RGB signals are fed from scart 1 via
connector Xa5 which is connected to the connector Xq7
on the main board.
Adjustable Audio Output module,
The audio switch ICa3 selects the signals either from Scart
TA7003, OVGA� or from the camera connector. The connector
Xa2 is linked to the connector XA4 (on the local control)
The adjustable audio output (line output) module TA700
and Xa3 to the connector Xtta (on the main board).
makes it possible to send the TV sound to an external am-
The voltage level on module pin 3 determines which con-
plifier using the tone and volume controls of the TVOs own
nectors the RGB and audio signals are taken from.
remote control.
The control voltage is taken from the teletext circuit (pin 7,
The left and right channel audio signals are fed via a FET
GPO), onward via connector Xq5-3 (on the main board)
pair, tta1 and tta2, to the op-amplifier icta1. Due to the nega-
and Xa1-3 (on the module). The RGB switch ica2 is con-
tive input, the amplifier inverts the signals. Amplified sig-
trolled via pin 5 and the audio switch with the voltage lev-
nals are then fed via another FET pair, tta8 and tta9, to the
els on pins 9 (=B) and 10 (=A). The logical low is about <3.5
output connectors Xt7 and Xt8 (RCA connectors).
V and logical high about >9 V with a +12 V supply voltage.
These FET pairs prevent possible unwanted switching
The GPO (general purpose output) operates as a three state:
peaks from the audio processor from reaching the exter-
high, open and low.
nal audio amplifier.
When the GPO is high, transistor ta2 conducts and pulls B
The first pair, tta1 and tta2, eliminate positive disturbance
low, diode da2 and transistor ta4 conduct, thus A and pin 5
peaks (internal diodes) and due to the inverting feature of
of ica2 are low. As a result of this combination, both the
the op-amplifier, the second pair, tta8 and tta9, prevent
RGB and audio signals are taken from scart 3.
negative peaks coming from the audio processor.
When the GPO is open, ta2 does not conduct and B is high,
da2 and ta4 conduct, thus A and pin 5 of ica2 are low. RGB
Switch on / off damping
signals are taken from scart 3, but audio signals are taken
The FETs also operate as mute (damping) switching com-
from the OVGA� connector.
ponents during switch on and off.
When GPO is low, ta2 does not conduct and B is high. Di-
When the receiver is switched on, the +12 Vp causes (via
ode da1 conducts and pulls the anode of da2 low. Diode
transistor tta5) the positive input on pin 5 of icta2 to go
da2 does not conduct, neither does transistor ta4, and A
high faster than the negative input on pin 6. This means
and pin 5 go high. Now the RGB signals are taken from
that the output pin 7 is high, and transistors tta6 and tta7
scart 1 (via Xa5) and audio signals from the camera con-
conduct holding the gates of the FETs low. A short time
nector (via Xa2)
later when capacitor Cta17 has charged, tta5 no longer
conducts and the voltage on pin 5 falls below that on pin 6.
GPOBARGB inAudio in
The output pin 7 is now low, and transistors tta6 and tta7
do not conduct. The first FET pair gets their gate voltagesHighO0OO0OScart 3Scart 3
via resistor rta24. The second FET pair has a small delayOpenO1OO0OScart 3OVGAO
since their gate voltage is taken via transistor tta4, resistorLowO1OO1OScart 1Camera
rta20 and capacitor Cta15.
When the receiver is switched off, pin 6 of icta2 immedi-
Scart 3 module, TA711
ately goes low, but pin 5 stays high due to the charge of
capacitor Cta18. The output pin 7 is therefore high and the
The scart 3 module is similar to the TA710 described above,
FET pairs are switched off.
but without the VGA-audio function. Otherwise the func-
tions are identical.
Line output status
The other half of the op-amplifier icta2 operates as a line
output status switch. When the output connectors are not
used, the additional contacts (on the connectors) hold the
negative input pin 2 low via resistors rta17 and rta18. This
means the output pin 1 is high, transistor ta9 (on the main
board) conducts and holds microcontroller pin 3 low (in-
active).
When a plug is connected to the connector, the additional
contact disconnects resistor rta17 / rta18 from ground. This
causes a higher voltage level on pin 2, and output pin 1
goes low. Now transistor ta9 does not conduct and
microcontroller pin 3 is high. This enables the selection of
three different mute states:
- Line output operates, but TV speakers are muted,
- Both line output and TV speakers are muted
- Both line output and TV speakers operate (no mute). |
ACEC
