Technics SL7 won’t auto-stop after playing 45s/singles

[Mwelliott]

I’ve spent the day dismantling, cleaning, lubricating the tonearm mechanism of an old SL7 I bought recently. It sounds fantastic - I’m delighted. (Thanks to everyone who out videos on YouTube!)

It works beautifully except after playing 45s it doesn’t auto-stop. It does with LPs. I thought it was to do with the auto-stop adjustment but it isn’t. The tonearm travels to exactly the same point  - in fact a bit further into the label on a 45 than on an LP.

So anyone know the problem? It can’t be to do with the tonearm mechanics. It must be that the deck recognises it’s a 45, changes speed and size but something doesn’t function properly.  Any ideas?

[David_AVD]

That does seem odd. Maybe check that the signal from the end switch really does change state when the end of the 45 RPM cycle is reached.

Another thing to try is run the 12" disc at 45 RPM and the 7" disc at 33 RPM and see what the behaviour is. Does the lack of end stop follow the speed or the disc size?

[Mwelliott]

Good idea! Will try F report back.

[Mwelliott]

* will try it and report back!

[Mwelliott]

Hi, I did some checking:
 - 33rpm & 45rpm 12" records play and auto stop perfectly
- 33rpm & 45rpm 7" records start perfectly but don't auto stop
- when the turntable recognises it's playing 7" record at whatever speed, it won't auto stop.

So the optical sensors know to start a 7" record in the right place but somehow deactivate (or don't activate) the auto stop mechanism.

I'm probably being dim but I can't spot the problem. Any ideas?

[Haenk]

Is it supposed to auto-stop on the 7"s at all? Does it say so in the manual?

[David_AVD]

I haven't checked the schematics in detail, but it looks like there are 3 optical sensors that sense the disc size.

Maybe check that area to make sure there's nothing untoward going on there.

[Mwelliott]

Yes, it is supposed to auto stop on any size record.

[Mwelliott]

Thanks David. Thing is that the sensors can detect when its a 45rpm/7" record. I can't imagine that the auto stop would be connected to the optical sensors as these just tell the deck where the drop the stylus and what speed to play - both these functions work on all record sizes. The auto stop works for 12" but not 7" - weird!

[dmills]

Note that the centre diameter is different for the LP and single per the RIAA standards, so there should be some either mechanical or electronic hardware that differs between the two media.

IIRC the difference is about a 1/2 inch in the diameter of the label.

[darkspr1te]

Thanks David. Thing is that the sensors can detect when its a 45rpm/7" record. I can't imagine that the auto stop would be connected to the optical sensors as these just tell the deck where the drop the stylus and what speed to play - both these functions work on all record sizes. The auto stop works for 12" but not 7" - weird!

Looking at the schematic and service manual there are a few adjustments that can be made and also the position angle sensor is different between 7" /12" marked as H1 and H2 located on the stator frame. However the auto return switch is the same between the two and the manual mentions that if any size record has a issue to adjust S307 which is a dial located under the smoked clear cover and gray plastic cover meet. This adjustment also includes inertia adjustment for the switch by changing it's angle. 
There is also a guide to signal waveforms you should see on many of the IC's and what values the switches produce in a truth table.

P.S service manual is on manualslib.com
darkspr1te