Cheap oscilloscope for setting up a Technics SP-10 - diyAudio
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Old 23rd June 2011, 01:48 PM   #1
johnm is offline johnm  United Kingdom
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Default Cheap oscilloscope for setting up a Technics SP-10

Hi folks!

Hoping somebody out there can help - I have just got hold of a lovely Technics SP.10 Mk.II turntable and PSU.

It works fine and all runs to speed.

However when checking out the capacitors underneath the turntable there are a few with 'green legs' so they all obviously need to be replaced immediately. I have a complete set of replacement electrolytics on order for both the turntable and the PSU.

Whilst the seperate PSU is very easy for an electronics layman to set up with just a multimeter, the turntable is a different prospect.

According to the service manual one needs a dual trace scope. Unfortunately I haven't got much money to spare at the moment, but I do need something that'll allow me to adjust the SP-10 Mk.II to the following:

Click the image to open in full size.

My question is, would the following VERY cheap PC Oscilloscope by adequate for just setting these two adjustment points:

NEW 2 Channel PC Computer Digital mini USB Oscilloscope | eBay UK

Many thanks!

- John


P.S. Full service manual available here: http://downloads.nakedresource.com/v...ro_service.pdf
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Old 23rd June 2011, 02:23 PM   #2
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The scope you posted only claims a useable frequency response to 3kHz...in order to set the above timing relationship to an accuracy of +/- 0.1ms I would want to use a scope with a bandwith in the low MHz range. In my experience if you replace the caps with parts of matching specification there is a good chance it will work without adjustment. These pots have probably not been disturbed since the TT was new.
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Old 24th June 2011, 10:57 AM   #3
johnm is offline johnm  United Kingdom
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Thanks for your reply Kevin.

DId you mean that - in general - caps can usually be replaced like-for-like without any adjustments being made, or have you had experience doing this with the SP-10?

Just read the service manual and it states:

"If you repair the Control circuit board or the Drive Circuit board, you have to adjust VR101 and VR102".

Thankfully the bad caps are not on any of those two boards, so I think I'll be OK just replacing those for the time being.
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Old 24th June 2011, 12:28 PM   #4
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Another project John So it would matter if the gain of the Sony was lowered

I agree with Kevin that it will work without any adjustment... I haven't looked at the circuit but what you posted is typical of older Japanese stuff. Hall effect DD motors in many early VCR's had similar adjustment procedures.

If the pots were a mile off then the motor would tend to "kick" as it fights the servo. Just leave them be I would say or use the "proper engineers" method of setting to the midpoint between the two points where lock is lost
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Old 24th June 2011, 01:33 PM   #5
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Quote:
Originally Posted by johnm View Post
Thanks for your reply Kevin.

DId you mean that - in general - caps can usually be replaced like-for-like without any adjustments being made, or have you had experience doing this with the SP-10?

Just read the service manual and it states:

"If you repair the Control circuit board or the Drive Circuit board, you have to adjust VR101 and VR102".

Thankfully the bad caps are not on any of those two boards, so I think I'll be OK just replacing those for the time being.
That was a very blanket statement.

In any circuit where the capacitor is used as a timing or tuning element, the circuit will almost invariably have to be adjusted.

The Service Manual, quite correctly, states that any repair to the Servo Board may require setting up of the board afterwards. Especially if the pots have been disturbed or replaced.

If the caps are simply decoupling or smoothing, then no adjustment will normally be necessary.
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Old 24th June 2011, 02:36 PM   #6
johnm is offline johnm  United Kingdom
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Thanks Andy, and greetings Mooly

I guess it would be handy to know for future reference - and anyone else who ever happens to be in the same situation as myself - which caps inside the actual deck could safely be replaced without having to worry about making any adjustments (assuming the unit was working well before!), and those which might well entail having to adjust the unit with an oscilloscope.

Recapping the separate PSU is comparatively simple and only requires a multimeter to adjust two voltages so I'll be able to do that OK.

Mooly: yep I'll leave the internal gain of the Sony WELL alone haha!
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Old 24th June 2011, 02:43 PM   #7
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I have a 30+ year old Technics SL1300 with a similar control system and adjustment procedure which had slow speed drift issues. I replaced all of the electrolytics in the power supply and it locked right in without any adjustments other than centering the coarse speed pots. The caps in question are voltage stabilizers which do not critically impact the timing synchronization.
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Old 24th June 2011, 04:12 PM   #8
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In any case, take great care replacing the caps. As the SP-10 is from the 70ies, it's likely using card boards (paper pcbs) where traces lift off extremely easy. (Not like todays fiberglass boards that are close to indestructible).

Better take great care than repair the traces with wires.

Otherwise, enjoy! Hannes
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Old 26th June 2011, 01:11 PM   #9
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Thankfully didn't manage to lift any traces, and also used a fairly low wattage iron (25w) so that probably helped.

Completely recapped the external PSU and set the voltages for that.

Also recapped two of the boards (the ones with the caps that looked past their best - green legs!). What a swine that was - desoldered the caps OK. But no matter how much I cleaned and defluxed the solder pads the new solder would instantly start 'bubbling' and set whilst bubbling. Had to resolder several caps until I was reasonably happy with the solder joints. Wondering if there's some reaction between the solder and the PCB material or something? Very frustrating!

Still all back together now and appears to be working fine

Last edited by johnm; 26th June 2011 at 01:13 PM.
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Old 26th June 2011, 02:17 PM   #10
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If I wanted to get a simple, basic oscilloscope for setting up this deck properly (which might also help with the odd future project too) would this be up to the task:

Hitachi Battery Oscilloscope V-209 20 Mhz | eBay UK

There's also a list here:

Oscilloscopes

Unfortunately my budget is less than 100...
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