TL Audio VTC - Manual (Page 50)

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switch inner. Failure to ensure correct alignment may result in the switch cap springing off suddenly
if the switch is operated quickly.
The push buttons are controlled by similar circuits. For example, the Control Room “L+R” push
button, SW2, is debounced by IC1B and toggled by the flip-flop IC2A (see CD1351 sheet 2). The
output from IC2A is used to turn on the LED via Q2. The flip-flop array is initialised to a pre-
determined state at power-on by the “RESET” signal from IC15A.
The toggled signals, “CR L+R~”, etc are active low (as identified by the label “~”), and are gated by
IC13C, etc (CD1351 sheet 4) to produce active high signals taken out on CN18 to PC352. The gating
at IC13C is determined by the state of signals “PFL” and “STD SOLO” i.e. if PFL is active or the
studio is soloed, the main Control Room sources are inhibited. Solo In Place or PFL mode is
controlled by IC7A (CD1351 sheet 2), generating the signals “SOLO MODE”, used to disconnect the
PFL buss on PC336 (see above) and “SOLO EN” which is routed out onto the input module
backplanes, PC337. Switching the Control Room and metering outputs over to the AFL/PFL buss is
controlled by the signals “PFL” and its compliment “PFL~” (CD1351 sheet 4). The gate IC14C
activates switch over only if Solo In Place is not selected, using the “SOLO” signal. “PFL SIG” and
“AFL SIG” are active high, diode OR’ed signals, activated from the various solo switches on the
console.
The Studio source selection operates similarly to the Control Room selection, but with an added logic
multiplexer to perform the Studio “Follow Control Room” function. “Follow CR” is generated by
IC6B (CD1351 sheet 3), and controls the gates IC17A/B, etc.
Talkback and Control Room dim are controlled by the signal “T/B ON” at CN18 pin 12. This signal
is either momentary if jumper J2 is fitted (the default setting), or latching if J1 is fitted. “T/B ON” is
also taken from PC351 on a flying wire loomed with the talkback microphone cable to PC348 on the
upper Master Module. If talkback does not appear on the outputs but the switch illuminates, check
that the talkback destination is selected on the upper Master Module and the output fader is open, and
that the flying cable is connected to PC348.
The logic power supplies on CD1351 are labelled VL+ and VL-. These voltage rails are derived from
the master section +15V and 0V respectively, but are decoupled from the audio circuit supplies by
R18, R19 and C28, etc.
4.15. External Monitoring Inputs.
The console has three stereo monitoring inputs: 2TA, 2TB and EXT. The inputs are on jack sockets
on the rear of the master section (or patchbay), with balanced receiver located on the upper master
backplane, PC355 (see CD1355 sheet 5). The two track returns are dedicated stereo inputs, but the
EXT input is normalled for stereo or mono operation.
Each of the external inputs is set to +4dBu nominal sensitivity by default, but may be changed to -
10dBu by fitting jumper links to PC355. These jumpers may be accessed by propping open the upper
master module.
The links that should be fitted are:
2TA:
J3 and J6,
2TB:
J2 and J5,
EXT: J1 and J4.