Table of Contents
Page
1. Introduction (Concept and cautions of troubleshooting) 4
2. General description
2.1 Composition 5
2.2 Flow of signal 6
2.3 Control of SW OUT REMOTE 7
2.4 Flow of signal in transmission 7
3. Input/Output actions
3.1 Actions of switches 8
3.2 Actions of external control signal output ports 9
3.3 Actions of CW audio demodulator 10
3.4 Change of CW transmission speed 11
4. Troubleshooting
4.1 Trouble of built-in display 12
(A) No display 12
(B) Fluctuating display 14
(C) Abnormal external display 15
4.2 Trouble of CRTC block 16
4.3 Trouble of computer block 19
4.4 Trouble in CW transmission 20
4.5 Trouble in CW reception 20
4.6 Trouble RTTY 21
5. Description of MODEM printed circuit board performance
5.1 Demodulator 21
5.2 Modulator 22
5.3 Baud rate clock unit 22
5.4 MODEM printed circuit board block diagram 24
6. Troubleshooting of MODEM printed circuit board
6.1 Demodulator 25
6.2 Modulator 28
6.3 Baud rate clock unit 29
7. Keyboard troubleshooting (KB-685E, KB6850)
7.1 Troubleshooting flow chart of keyboard (PCB No. 820226-1) 30
7.2 List of keyboard output codes 32
8. Description of former MODEM board 33
9. Parts list 35
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