THORENS PC 650 - Page 11

Logic Elements
The logic circuit employs double NAND gates, the inputs E14 of which are connected to the buttons in
the control array. The terminal A is the output of each gate combination. The input E2 is connected to
the second, internal output.
The logical relationships for each individual NAND gate
may be expressed as follows:
A= 1 when E, =0, Eg =0, or Ey = EQ = 0
A=Owhen Ej =E9=1
Thus, if the input E4
of the double combination is set to 0
(input command), then
A=1
and therefore E9 = 0 (from the upper NAND gate). Eo
As soon as Eg = 0, A is held to 1 even after the button is
released and E 7 reverts to 1 (latching action). Ey
An input command 0 thus causes the corresponding command bus (designated in the circuit diagram
with STOP, Vorl., PLAY, RECORD, Riickl., and PAUSE) connected to the output A to be set to 1.
At the same time, the input command 0 sets the functions which are to be canceled to 0 through a
diode array.
The Production of Control Commands
STOP
PAUSE
RECORD
When the button contact S 101 is closed, the NAND gate output IC 1704 (10) is
set to 1. Because of the latching action, this state is maintained even after S 101 is
released and IC 1704 (8) returns to 1 through R 1721. Closing the contact sets
all other command buses to 0 through D 1709, D 1715, D 1720, D 1731, and
D 1736. In contrast to the other (run’’) functions, the state 1 at iC 1704 (10)
does not constitute a command. Rather, the absence of all other commands
causes the tape to be stopped, as described below under ’’Tape Transport Stop”.
Operation proceeds in the same manner as STOP when the contact S 104 is
closed; however, the RECORD bus is not set to 0.
Connection S 1709 is fed from +12 V through R 196 (VM 1) for all transport
functions except PLAY, bringing T 1702 into conduction. Closing contact S 102
causes approximately 0 V to apear at the collector of T 1702. As a result, D 1710
and D 1732 conduct, cancelling the Fast Forward and Rewind functions. D 1753.
conducts, turning T 1705 off. Because of the latching action, IC 1703 (4) and
thus the RECORD output S 1716 are set and held to RECORD command 1.
As soon as the RECORD button is released, T 1705 conducts because of the
positive voltage (command 1) at S 1716. The emitter of T 1705 is thereby pulled
toward +12 V. This voltage prevents IC 1702 (6) from being set to 0 when the
PLAY contact is closed (over the relatively high impedance R 1748). The re-
cording function can be initiated only when S 102 and S 105 are closed simul-
taneously, since T 1705 will be turned off at that moment. A O appears immed-
iately at IC 1702 (5) , so that subsequent conduction of T 1705 is of no con-
sequence.
If the PLAY function has already been initiated, T 120 (VM 1) conducts, turning
T 1702 off. Closing the RECORD contact has no effect on operation in this
case.
A cassette without rear breakout lugs will not close the recording inhibit contact.
In this manner, transmission of a RECORD command to the Power Control Board
via S 1716 is prevented (VM 1).
St i a a a