Excelent scan job. It's a fully detailed service manual of this model.
Text excerpt from page 20 (click to view)
2.2.5. System/Key Circuit
(1) AUTO STOP
Auto Stop YES Does the SW30 waveform appear at the IC501 Pin 24? YES Do the T-UP Reel Pulses appear at the IC501 Pin 4? YES Replace the IC501. NO Do T/UP Reel Pulses appear at the Q514 Base terminal ? YES Replace the T/UP Reel Sensor (RS501). NO Does 5.0V appear at the RS501? YES NO NO Check the Drum Motor signal.
Check the Q154 Power Circuit.
(2) The unstable loading of a Cassette tape
The unstable loading of a Cassette tape YES Is 12V applied to the IC502 Pin 7? YES Does the �H� signal appear at the IC501 Pin 57 during inserting the CST ? YES Does the �L� signal appear at the IC501 Pin 19 during inserting the CST? NO YES Does 6.8V occur at the IC502 Pin 2 during inserting the CST? NO YES Check the Deck Mechanism. Replace the IC502. Check the IC501 Pins 74, 75, 76, 77. Check the CST SW and the peripheral circuitry. NO Is 5.3V applied to the R544 ? YES NO NO Refer to �SMPS CAPSTAN 12 Volt Trouble Shooting�.
Refer to SMPS 5.3VA troubleshooting.
Caution : Auto stop can occur because Grease or Oil is dried up
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