THORENS PC 650 - Power Control Board VM 14

17. Power Control Board VM 14
The commands from the Logic Control Board VM 17 appear at the input connections S 1418, S 1419,
S 1420, S 1421, and S 1422. They are inverted by the NOT elements of IC 1401 to produce internal
control commands. The Power Control circuitry produces the necessary DC voltages on the output pin
connections.
Holding Magnet
S 1403
S 1405
Record Voltage
S 1404
Reel Motor
S 1406
S 1407
Transport Stop
S 1416
Control Functions
STOP
PAUSE
RECORD
PLAY
Fast Forward
STOP PAUSE RECORD PLAY F. Fwd. F. Rew.
OV OV app.+ 15 V ov OV
OV OV app. + 19 V OV OV
OV +12V OV OV OV
+12V +12V +12V +12V app.+ 6V
+12V +12V app.+ 7V app.+ 6V +12V
OV OV app.+ 2V +1.43 V +1.43V
This function is initiated by the absence of all commands 1 from VM 17. The reel
motor is stopped, initiating the Tape Transport Stop function on VM 17. The re-
sulting command 0 at connection S 1420 (from S 1718) causes a command 1 to
be produced at IC 1401 (12), turning off T 1402 and thus releasing the holding
magnet (3192005).
Operation proceeds in the same manner as STOP; however, the RECORD func-
tion is not disabled.
The command 1 at connection S 1418 produces a command 0 at IC 1401 (13),
bringing T 1415 into conduction and thus feeding the Erase/Bias Oscillator
through S 1005, the Test Generator over St 1501 (VM 1), and the Monitor cir-
cuit (VM 1) each with +12 V.
The command 1 at connection S 1419 produces a command 0 at IC 1401 (12).
T 1404 is turned on through D 1408, likewise turning on T 1407 to power the
reel motor. The tape tension is determined by. the setting of R 1416. T 1402 is
simultaneously turned on to power the holding magnet. The sudden voltage in-
crease at the collector of T 1402 is conducted through C 1402, turning on T 1406
and T 1405. The low-impedance state of T 1405 enables the magnet to pull in
(S 1403). C 1402 then charges, T 1406 and T 1405 are turned off, and the mag-
net is held on through R 1414 (holding current reduction).
The command 7 at connection S 1421 is conducted through T 1414 and D 1421.
Because of the charging-time constant of C 1407, acommand 0 is produced with
a delay on IC 1401 (11). As in the case of PLAY, T 1404 and T 1407 are turned
on to power the reel motor. An undelayed command 0 appears at IC 1401 (10);
the voltage divider R 1411, R 1418, and R 1441 is turned on through D 1413.
The resulting voltage at the cathode of D 1427 constitutes the reference value
for the tape tension. The actual value is represented by the voltage on R 1419,
which is proportional to the motor current and controls T 1410. If a binding
cassette causes the voltage on R 1419 to rise because of increased motor current,
T 1410 and thus T 1409 will be pulled further into conduction. The reel motor
can then draw more current.