Samsung SV-DVD50 Service Manual page 115

(20) Trouble Detection
The trouble detection circuits are provided to protect the from damage (Fig. 7-15). The reel lock sensor detects
incorrect rotation of supply and take up reel. The reel lock sensor consists of the disk and photo sensor installed at
the bottom of the reel disk. the disk has 6 or 8 shielder parts and the photo sensor consists of the LED and photo
transistor assembly. When the light is shielded by the the shielder or enters the photo transistor, the output is
obtained from the photo sensor. IC601 measures the period of the pulse. When it is 4 seconds or more during
record/play, the VCR enters the reel emergency mode.
The VCR maintains the unload-power-on state in the reel emergency.
R691
(21) Cylinder Lock Sensor
Cylinder lock sensor detects abnormal rotation of the cylinder motor. Cylinder FG pulse is supplied to pin97 of
IC601. MICOM measures the period of the pulse in the play/record, search and trick play models. When H'd
S/W frequency is less than 10Hz for 5 seconds, the VCR enters the stop mode.
(22) Tape End Detection
When supply end sensor detects the transparent section at the end of tape, the VCR enters auto rewind mode,
except during timer recording and OTR mode. The cassstte LED emits light through the transparent section of
tape to the photo transistors, which are installed at both ends of the cassette. When take up end sensor detects
the start section of the tape during reverse search and rewind, the VCR automatically goes to stop mode.
R676
R675
C633
R678
R679
R682
Fig. 7-15 Reel and Cylinder Lock T.END/S.END Sensor
R677
66
75
74
C634
98
99
Circuit Operating Descriptions
7-13