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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 9th Aug 2018, 8:29 pm   #1
nmiddlemass
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Default Sony SL-C20 - Issue with Play FF RW

Hi,

I've recently been fortunate enough to get a Sony SL-C20UB Betamax Recorder. Cosmetically it is in great condition but a bit grubby after years of storage.

After an examination, the unit powers up. It accepts a tape which laces up well.

The issue with this machine is with PLAY, FF and RW. In all cases the machine starts to work but after a couple of seconds it stops. I have visually checked the pendulum and to my eye it looks OK and engages as it should (I think) on each operation.

A separate problem which may be connected with the issue is that the tape appears to look a little slack after it has been through the pinch roller (apologies if that is a dreadful description). Also when ejected the cassette ejects from the unit but the tape is not wound tight in the cassette body and it gets very slightly caught in the mechanism and tape door.

I've seen on another site some possible causes around a silicon fuse but this is working fine.

I can only assume it has something to do with that pendulum.

If anyone has any experience of these machines and could possibly give me some pointers I would be grateful.

Many Thanks.

Neil
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Old 9th Aug 2018, 11:42 pm   #2
martin.m
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Default Re: Sony SL-C20 - Issue with Play FF RW

Hi Neil
The pendulum does cause problems on this range of VCRs. Remove and examine it carefully to make sure it is straight. Over time the plastic distorts and the whole assembly can curve upwards. The new replacements from Sony were made of thicker plastic to stop this happening. You could try straightening the pendulum by holding it with pliers and sinking it into a cup of very hot water while applying pressure for a few minutes. I've seen this done but it should only be regarded as a temporary repair. Hope this helps.

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Old 10th Aug 2018, 6:04 pm   #3
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Default Re: Sony SL-C20 - Issue with Play FF RW

Hi

I recall this model also used a hall sensor in the video head stator motor. The glue holding the hall sensor in place starts to conduct after several years causing a short. If the head turns freely by hand but stops dead in fwd fwd and play then I would suspect the hall sensor.

Rob
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Old 30th Aug 2018, 9:29 am   #4
nmiddlemass
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Default Re: Sony SL-C20 - Issue with Play FF RW

Thank you for the replies..

Having looked at this issue in more detail, I am fairly sure the issue is with the Halls sensor. The head motor isn't spinning..

I've seen online that this glue can be removed but I am having real trouble removing the rotor assembly. The service manual asks for a nut and a washer to be removed which should then allow me to take out the rotor and access the sensors. However, the rotor will not move. Everything spins freely as it should.

Could this be time hardened lubricant? Any ideas how to remove it?

If anyone has any advice on this I would be grateful.. I don't want to make matters worse by applying too much force..

Also.. would anyone know where to source replacement sensors or any modern equivalents that would do the same job?

Thank you.
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Old 30th Aug 2018, 9:55 am   #5
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Default Re: Sony SL-C20 - Issue with Play FF RW

Don't start taking the motor apart until you are sure the sensor is faulty. If the PG sensor isn't working (the one in your picture) the motor will still spin up but then stop after a short while, so its probably not that which is wrong. If the hall sensors which commutate the windings are faulty then the motor will limp round for a bit if you spin it up by hand when it is supposed to be working, or at least some resistance will be felt from the coils which are energised. Do your test in 'still' mode, this excludes things like the capstan motor FG sensor and the reel sensors.

The diagram will show which motor pins have the hall sensor outputs on them. Energise the sensor from a bench supply (motor disconnected of course) and scope the outputs as the shaft is turned. Only then, if something it proved to be incorrect, is it worth dismantling the motor. This is not a risk-free operation, it is possible to damage things like the head tips when the nut on the bottom of the shaft is released.

Don't rely on the internet to do your diagnosis for you, it is usually wrong. Make your own tests instead, its the best way.
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Old 30th Aug 2018, 10:42 am   #6
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Default Re: Sony SL-C20 - Issue with Play FF RW

The last total motor failure I did was on an sl-c9 which uses the same motor, in this case the electrolytics on the motor pcb were totally open circuit. Its worth checking all the soldering on the board, it was very bad with numerous dry joints, possibly from vibration ?
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Old 31st Aug 2018, 8:22 am   #7
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Default Re: Sony SL-C20 - Issue with Play FF RW

Now that you've removed that centre nut, the only thing holding the rotor in place is the magnetic attraction of the disc to the stator. You have to get your finger tips under it and try to lever it up, but the pull is very strong. Don't be tempted to use screwdrivers etc., you will damage something. Once it moves just a small amount, it will let go and come off freely.

Mark.
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