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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 31st Mar 2018, 12:58 am   #1
Michael Maurice
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Default Technics SL7

When I got this, I thought it would be an easy repair, no such luck.

The original problem was that the belt was worn, so I replaced it, but now I have a problem that the arm will not move across the record. It will if you press the << key and if you've moved it to the centre, it will move back, but not when its playing a record.

If you look at the attached diagram Q306 is not being switched on, this seems to go back to IC301 whose port is not going high.

In addition, my main board does not appear to have D321 or Q322 fitted.

Does anyone know whats going on?
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Old 31st Mar 2018, 12:46 pm   #2
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Default Re: Technics SL7

Quote:
Originally Posted by Michael Maurice View Post
..now I have a problem that the arm will not move across the record. It will if you press the << key and if you've moved it to the centre, it will move back, but not when its playing a record.

...Q306 is not being switched on, this seems to go back to IC301 whose port is not going high.
There are a couple of possibilities. If the arm has dropped and is trying to play a record, arm release solenoid circuit Q317 will have been activated from Q306 turning on. If the arm does not move across from play then worth checking the rest and end micro switch S306/307. Worth checking to see if IC301 output port ever gets pulsed after pressing play button.

Motors on these are notoriously unreliable due to running at a very slow speed where dead parts of the commutator often develop. Temporarily disconnecting the motor and running on a power supply at rated voltage may naturally remove the dead spots.

Rich
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Old 31st Mar 2018, 11:06 pm   #3
Michael Maurice
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Default Re: Technics SL7

Thanks for your help Pete.

My main board is totally different from the circuit diagram.

Q306 does in fact turn on as it should but the sled motor drive is contained in a BA6109 IC which is normally used to drive loading motors on VCR's.

So i'm rather stuck.

The motor itself is OK because if you press the << or the >> keys the arm moves. It just wont move when its playing a record.
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Old 1st Apr 2018, 11:00 am   #4
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Default Re: Technics SL7

Michael I am not sure how it is supposd to work.
obviously the stylus moves the arm fractionally then the arm moves and so on.
on some decks when the arm was moved by the stylus a shutter moved out of the way of an optocoupler (sometimes a lamp and LDR) and thus the moror moved the arm.
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Old 1st Apr 2018, 12:43 pm   #5
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Default Re: Technics SL7

That is how it works Peter, its actually quite difficult to run checks but from what I can see, moving the arm around does produce a signal from the optocoupler. What I cant decipher is the how the signals get from the detector to the motor run chip.
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Old 7th Apr 2018, 11:03 pm   #6
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Default Re: Technics SL7

I have been trying to get a SL-7 working for almost a year. This, too has a main circuit board which differs from that shown in the service manual. TBH, the deck has been put to one side for maybe 6 months because of the problems with it. The linear tracking arm is moved between two micro-switches which essentially detect the start and end of a record. At the L.H. end of this assembly is a small circuit board incorporating a slide which allows for manual setting of record diameter, and a motor which drives the arm mechanism via a small drive belt and a metal pulley. The pulley tends to work loose and come off it's shaft, which results in no lateral movement of the pickup arm, since the shaft incorporates a worm drive. There is a thread on here about this particular SL-7 and it's problems, but it's only to do with the arm drive problem, which was solved by securing the pulley to it's shaft with a few drops of a 'Loctite' adhesive designed for this type of job.

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Old 7th Apr 2018, 11:23 pm   #7
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Default Re: Technics SL7

Well I seemed to have sorted my deck out thanks to a very helpful chap on ebay.

Firstly I tried to fit a 25mm belt but it was too loose, so I fitted a 20mm round belt but that was the cause of the problem it was too tight.

I bought a belt from this ebay seller, only to find it was 25mm and too large, in fact it wasn't, the motor had moved closer to the worm wheel. I manged to move it to the correct position, refitted the belt and worked OK.
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