SP10 Troubles

Love it or hate it, it just won't stop
RussellS
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Post by RussellS » Tue Oct 30, 2012 10:50 am

Me back again...

Some more experience with the SP10s. I was given two, one in sad condition and the other in fair condition, both without power supplies (no SH10s). I intended to make one good one out of the pair.

I built a power supply using a scrap-box transformer (15-0-15v 2a and 6v 3a) with voltage regulator chips: 5v 1a for the 5v rail and scrap box 20v 1a plus a zener or two and a high power NPN transistor to get voltage up to 32.5v and current up to 3a). A couple of suitable electrolytics on each rail and I was in business. In fact, all scrap-box except the 5v regulator and the 4pin connector. NB. No 140v rail because I was going to replace the failing or dud neon strobe tubes with LEDs.

The first table to go on the bench was the suspected dud.

In my earlier posts I have outlined my accidental shorting of the 5v rail to the 32v rail. 20 hours, 16 sockets and a few TTL chips later...

It responded to additional care but I couldn't get the signals on my scope to line up like the manual when adjusting VR101 and VR102. In fact, I discovered that, when I connected the scope probes (an old Philips dual beam scope) it actually influenced the signal shapes and timings, there must be some probe capacitance/resistance issues. I eventually found that adjusting VR101 while watching the strobe LEDs seemed just as effective (at 33.3 turn VR101 until table increases speed, then turn pot back until table decreases speed and then turn pot to central point of stable speed. Repeat on 78 with VR102. Please advise if you think this is shaky advice...

WATCH OUT for shorted probes. Probe points 0v, S and T are direct connections to the circuitry and are not isolated by resistors or whatever. I had to replace one transistor due to probe shorting (scrap-box again, thank goodness).

Apart from that, and a moment when a badly soldered +5v wire broke off and shorted on the plate, all went well. I went from happiness to despair about 4 times that afternoon.

I carefully oiled and cleaned up the bearings and it works 100%. The Technics label is gone long in the past (anyone know where I can get one?) but the table itself is essentially good.

The second SP10 responded well to a wiser and poorer man and I managed to get it humming, also with new LED strobe, without much difficulty.

So now I have one I use and a spare. Looks like my old Garrard 301 will not be missed so much any more...

Thanks for listening, I appreciate any comments if you think I have missed something.
I either do, or I don't. There is no 'try'.

Neal
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Post by Neal » Tue Oct 30, 2012 12:55 pm

Where your 'scope probs set to x1 or x10! :D

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Post by Neal » Tue Oct 30, 2012 12:55 pm

Where your 'scope probs set to x1 or x10! :D

RussellS
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Post by RussellS » Tue Oct 30, 2012 1:03 pm

Neal wrote:Where your 'scope probs set to x1 or x10! :D
I don't think they have that facility. They are straight connection to the BNC sockets on the front of the scope (labelled 10pF and 1Meg). Normally I have no problems but they definitely influenced the signals on test pins S and T. So much so that the calibration changed significantly when attached. At first I thought another failing component may be to blame but as soon as I removed the probes the table behaved like it should! :)
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Mike H
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Post by Mike H » Tue Oct 30, 2012 1:58 pm

Yes it's often overlooked that a 'scope loads the thing it's connected to. Albeit 1 Meg doesn't sound a lot, but it depends ~ quite likely the probe itself is 30pF (typical), so add that to the 'scope's input capacitance.

As Neal said a X10 probe will help a lot, 10 Meg and 3pF -ish, still not perfect though. The downside is it divides by 10 so needs a correspondingly more sensitive 'scope for small signals.
 
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Post by Neal » Tue Oct 30, 2012 3:04 pm

I mentioned it as one of my decks, the one I've re-capped throughout is sensitive the probe setting! The other with only the 'lytics replaced seems to be fine :?

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Post by RussellS » Wed Oct 31, 2012 7:19 am

Neal wrote:I mentioned it as one of my decks, the one I've re-capped throughout is sensitive the probe setting! The other with only the 'lytics replaced seems to be fine :?
I have not recapped either deck as they seem very quiet and stable. I did have one interesting though.

I was playing an old Bing Crosby 78 and the cartridge and needle was fluttering and almost bouncing off the shellac as it played. I felt that despair come on again (you KNOW how many screws you have to undo to get back inside) and I put finger tips on the table. It was vibration free. So I pulled out another Bing Crosby 78 (same Brunswick label) and tried that. Much, much better but not perfect. So I pulled out a Parlophone 78 and tried that. Perfect, no rumble or flutter at all. It seems that the Brunswick cutting machine was full of flutter all those years ago!

5th relief in as many days. :)
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Mike H
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Post by Mike H » Wed Oct 31, 2012 2:42 pm

This is the problem with testing things isn't it, first you need a correct source signal. :D

E.g. you assume the cutting machine was OK. Very interesting though. (That it isn't)
 
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Post by Neal » Wed Jan 01, 2014 2:09 pm


Wolfgang Felber
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Re: SP10 Troubles

Post by Wolfgang Felber » Thu Nov 09, 2017 12:53 pm

Hi to all, I am a newbie to this forum, my name is Wolfgang and I am trying to repair a SP10 MK2. This the second one, the first works fine so far. The second was completely dead when I got it. I now have it to the point where it runs but at hyper speed and I cannot turn it off unless I power it down and I have no control of the speed. The Strobe works which it didnt before. I have replaced all the electrolytics except for the large chassis mounted unit, this tested better the new one on the Peak ESR70 tester. I have replaced all of the IC's on the logic board except for IC 1. There is an additional board which was fitted by the Australian Broadcasting Commissions techs, no idea what it does. I can post a photo if that helps. This also has two IC's which I have replaced just to be sure. Because I have a functioning unit, I have been swapping and changing boards to try and isolate the problem board. It seems to come back to the logic board all the time. Both power supplies are fine, all voltages are good under load conditions. they both work on the good T/T. I have also tested the C19 and C109 to make sure they are OK and they tested slightly above the specified value. When I put the logic board from the bad T/T into the good T/T , I got speed control and it locked onto speed but I could not turn it off using the On/Off switch.
When first powered up the platter does not spin until switched on but then I cant turn it off. you press the on/off button the platter stops spinning, you take pressure off the button and away she goes at normal speed. I am open to any suggestions, Thank you.

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Nick
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Re: SP10 Troubles

Post by Nick » Thu Nov 09, 2017 11:15 pm

Try adding a 1k resistor in parallel with R221. I found that later logic pulled more current, the 47k that is normally feeding IC8 is too high a value. As the Flip Flop switches it pulls more current from the input causing a double count, the effect of that is it seems to do noting as its turning on and off in quick succession. Its possible the original logic did this as well but wasn’t fast enough to see the extra transition.

If that helps, I would also do the same with R261 for the same reason.
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Wolfgang Felber
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Re: SP10 Troubles

Post by Wolfgang Felber » Sat Nov 11, 2017 11:15 am

Hi Nick, thank you for your reply, before I fit the 1k resistor in parallel with the 4.7K resistor, I measured it in circuit and it was only .75K ohm. I fitted the resistor but it made no difference. still running at hyper speed and not turning off. The only IC that I have'nt replaced is IC 1, do you think I should?

Regards
Wolfgang

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Nick
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Re: SP10 Troubles

Post by Nick » Sat Nov 11, 2017 5:25 pm

All I can suggest then is checking the voltages are the various test points and seeing where they differ from what the manual says.
Resistance isn't futile it's V / I.

Wolfgang Felber
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Re: SP10 Troubles

Post by Wolfgang Felber » Mon Nov 13, 2017 4:43 am

Hi Nick, a small step yesterday, I managed to get the SP10 to stop and start. I did by replacing the IC 8 with a new one and fitted the 1K Resistor in parallel to the 4.7K resistor, at first it made no difference but with a new 74ls73 it works but only intermittently, I will try and put the other 1K resistor in tonight. Unfortunately it still spins at hyper speed, any ideas? The one thing I did notice was that when I press the speed buttons for the various speeds the strobe becomes dim with different speeds. There is no speed change. I think I shall try changing IC 1 tonight and see what happens.

Regards Wolfgang Felber

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