TELEREADER CWR-685E, Руководство по обслуживанию

Страница: 19 / 40

19
4.3 Trouble of Computer block
Check whether the Computer block is operating normally or not in the following procedure.
o The output level of pins 2, 4, 5, 6, of IC37 should be always H level as far as the Computer
is operating normally. When a pulse waveform of L level is observed on oscilloscope screen,
it means that the Computer is running away. Runaway of Computer is almost always ac-
companied by abnormal oscillation of the monitor sound.
o As far as the system is operating normally, the Computer reads the state of switches, and
varies the level of each Output port as follows.
a. When the RX/TAPE selector is set to RX side (since the switch is turned off, pin 4 of
IC40 becomes H level), pin 24 of IC28 is set to L level.
b. With the RX/TAPE selector at RX position, when the RESET button is pressed, pin 24
of IC28 is set at H level while the button is being depressed, and it is immediately
set to L level when the button is released.
c. When the RX/RAPE selector is set to TAPE side(since the switch is turned off, pin 4
of IC40 becomes L level), pin 24 or IC28 is set to H level.
d. With the RX/TAPE selector at TAPE position, while the RESET button is being press-
ed down, pin 24 of IC28 is set at H level, and immediately after the button is rele-
ased, the level is set to L for about 20 ms, and is then set to H again.
e. With the CW/RTTY selector at RTTY, when the SEND-AUTO-RECEIVE selector is set
at SEND (the switch is turned on, and pin 14 of IC40 becomes L level}, and pin 15
of IC27 is set to H level, and AFSK monitor sound is delivered. At the same time, pin
6 of IC27 is also set to H level. At this time, when an alphabetical or numerical key
is pressed on the keyboard, a corresponding code is sent out immediately, and the
frequency of AFSK monitor sound is also varied in tune with the code. In this state,
when the selector is set to AUTO or RECEIVE position (the switch is turned off, and
pin 14 of IC40 becomes H level), about one second later, both pin 6 and pin 15 of
IC27 are set to L level, and the AFSK monitor sound ceases.
f. With the CW/RTTY selector set at CW and SEND-AUTO-RECEIVE selector at SEND
position, when an alphabetical or numerical key is pressed on the keyboard, a corre-
sponding code is sent out immediately, and the monitor sound at 800 Hz is intermit-
tently delivered in tune with the code, and the CW LED flickers at the same time.
o Of the ICs on the main PCB, those having high frequency of trouble occurrences (breaka-
ges) are the following:
IC19 (SN74LS245)
IC7, ICS, IC9 (SN74LS157)
IC42 (MC3301, LM3900)
IC31 (MC6802, HD46802)
IC29 (2716 type E-PROM ... operation program written in)
IC30 (2732 type E-PROM ... operation program written in)
IC17 (2716 type E-PROM ... character pattern written in)
IC6 (TC4011)