Quantcast Sony SLV 757VC not read with a transparent leader. - digitalFAQ Forum
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  #1  
11-20-2020, 08:14 AM
promoter_2000 promoter_2000 is offline
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Hello everyone. My Sony SLV 757VC works regularly in everything but has, for some years now, a strange problem: when I insert a cassette with a transparent leader queue which, at the end of the tape loading, leaves the photodiode T (to the right of the compartment) or S uncovered (to the left of the compartment, if at the end of the tape) the mechanism no longer responds to any command and, after a while, the cassette is automatically ejected. When the two photodiodes are covered by the tape, everything works fine. If I cover with black adhesive tape both the central emitter led and the two lateral detection photodiodes, the play / rec starts regularly even with a transparent leader tail but, by rewinding the tape at the beginning, the commands no longer respond until I turn off / on the video recorder. I tried to clean the switch mode but it didn't help. The central infrared emitter LED works regularly (I see it lit by framing it with a ccd camera) and, by alternating the covers of the two lateral photodiodes, the mechanics respond regularly (but always crashing after rewind). From the tests done it seems to me that the central infrared emitter LED and the two side sensors work. Am I wrong? If LEDs and diodes work, as well as switch mode, why does the transparent tail block the mechanics? Thanks everyone for your attention.
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  #2  
11-20-2020, 12:18 PM
latreche34 latreche34 is online now
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How a bout the cassette detection switch, Every VCR has a different location for it. When you insert the tape do you get the cassette logo in the front display? When the problem happens, does the logo go away or flicker?
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  #3  
11-20-2020, 03:43 PM
promoter_2000 promoter_2000 is offline
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Yes, when the cassette is inserted the logo appears on the display and does not flash. When the problem appears, the logo is steadily lit without any flashing. By pressing the play button, the relative logo appears on the display and after a couple of seconds it switches off and the cassette is ejected. As I said before, if I slide all the transparent tail by hand and insert the cassette so that the first piece of magnetic tape obstructs the hole, the play starts immediately (this makes me believe that the right photodiode works regularly).
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  #4  
11-20-2020, 11:45 PM
latreche34 latreche34 is online now
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So what's the problem then. All VCR's move the clear leader to the inside of the spool, Why are you manually unspooling it?
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  #5  
11-21-2020, 02:32 AM
promoter_2000 promoter_2000 is offline
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To check if the problem was caused by one of the two faulty side photodiodes (or both). By doing so I verified that the transparent queue at the bottom of the tape does not give any problems (stopping the tape at the bottom of the cassette the vcr mechanics respond perfectly and this makes me think that the photodiode on the Supply side works properly). On the contrary, by rewinding the tape at the beginning, until the transparent tail is in front of the photodiode on the Take side, the mechanics of the 757 do not respond and eject the cassette; vice versa, if I run the transparent tail by hand to the beginning of the magnetic tape and then insert the cassette so that the Take photodiode is already covered, the mechanics work perfectly. This test, verified several times, makes me think that the problem is generated by the Take diode which, for some reason, sees but does not interpret the incoming infrared from the central LED (in the presence of the transparent tail), understanding only when it no longer sees the infrared (covered by magnetic tape). A half-functioning photodiode? It seems strange. A madness of mechanics that I can't explain to myself.
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  #6  
11-21-2020, 02:08 PM
dpalomaki dpalomaki is offline
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Quote:
...transparent queue at the bottom of the tape...
I don't understand what you mean by this? Clear leader at each end of the tape?
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  #7  
11-21-2020, 02:19 PM
promoter_2000 promoter_2000 is offline
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Quote:
Originally Posted by dpalomaki View Post
Clear leader at each end of the tape?
I apologize to everyone for the bad English (it's not my language; I'm using Google Translate).

That's right Dpalomaki: Clear leader at each end of the tape.
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  #8  
11-21-2020, 04:41 PM
latreche34 latreche34 is online now
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What's the original problem? If the VCR plays tapes correctly then why are you testing sensors?
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  #9  
11-22-2020, 12:25 AM
promoter_2000 promoter_2000 is offline
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It's true: the vcr reads and records regularly. The only problem is this refusal to "get going" when I insert a cassette with a transparent tape that is too long at the beginning (a defect that only appeared for a few years; before, even with these cassettes everything worked normally). In the area where I live, there are no more repair technicians willing to accept the device (and those already retired have told me that, in the era of 4K, I should have already thrown it in the garbage). For this reason, for a long time, I have been looking on the net for a solution to this defect which, I have seen, other owners of SLV 757 also complain (https://english.electronica-pt.com/repair-tips?ref=SLV757&marca=SONY&sintoma=). Unfortunately, up to now, I have not been successful. From the little that I have been told the origin of the defect could lie in a malfunction of the S and T photodiodes for this reason I have tried to investigate them with an empirical method (not having an oscilloscope).
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