Hello all, My Panasonic RQ-SX75 in mint condition keeps auto reversing forever. Every function works well, except this issue. I checked the traces from the photocouplers to the components they connect to and until the IC, all check out. It works well when I enter the service menu following the procedure in the service manual here: https://elektrotanya.com/panasonic_rq-sx75.pdf/download.html Here is a demonstration: What should I check next? Thank you in advance.
Have you checked that the photo transistor actually produces a signal ? Think the unit works when in service menu because in that mode the microcontroller ignores the reel rotation signal.
Thank you for replying. Any way to check it without an oscillator? Also may be unlikely because there are two of them in this unit, one for each direction. But I would never know. If there is no other way it may be the time for me to get an oscillator
Couldn't download the service manual. If there are 2 photo detectors, it's indeed unlikely both have failed. However, given both reels should rotate during normal operation, I think missing just one of the 2 pulses is enough to trigger auto-reverse. Best way to test is either checking the signal with oscilloscope or injecting a pulse yourself with a function generator. A simpler way would be to check the IR led (as these are usually what fails) with a camera (can be a phone camera) when in service mode. Is there anything in between these photodetectors and the microcontroller ?
Hello Valentin. Thank you for the tips. Let me add another link to the manual for reference: https://drive.google.com/file/d/1s9kL4fjmG6Qo0P6zOuNbNz-3j_xQ6ZAq/view?usp=sharing I followed your tips and seen with the camera that the leds of the photocouplers were not lighting up, and I also realized the battery check button of the device is not functioning. This took me to the point of tracing the IC475 DC-DC step up regulator which sends the voltage to both photocouplers as well as the battery indicator LEDs. It turned out the trace going to the ground pin (number 4) of IC475 was broken. I reconnected this to ground and issue is resolved. Below is the concerned part of the diagram: Here is the broken part on the pcb (i guess the black is just rust?): Here is the connection re-established (before UV mask): Sorry for low quality photos as I took directly from screen of the microscope. Thank you for the help!
