UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

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

Closed Thread
 
Thread Tools
Old 18th Dec 2014, 3:05 pm   #1
CHRIS_F
Tetrode
 
CHRIS_F's Avatar
 
Join Date: Apr 2014
Location: Merseyside, UK.
Posts: 57
Default Technics SL1200 MK2-A

Hi Guys, I'm not sure if I have a problem or not, the pitch controll on my Technics 1200's needed calibrating so I bought a service manual, I followed the instructions for pitch 0% adjustment first as follows.....set the pitch to the center position 0% attach a frequency counter between test point 27 and ground, adjust vr301 until frequency is 262.08 KHz then to set gain adjustment disconect connector CN102 attach meter test leads to pin's 5/6 on CN102 and adjust VR302 until meter reads 2.7k Ohms.

The pitch now seems to work correctly, but I noticed two things firstly my frequency counter was fluctuating between 262KHz and 263KHz I only have a 3 digit display so couldn't set it exactly at 262.08 it's fluctuating anyway. Seccondly this fluctuation seems to make the platter flutter ever so slightly, if I look at the strobe dots on the platter there is a back and forth movement it's only about 1mm or less, but I'm sure when the pitch is at 0% the PLL circuit should keep it locked rock steady.

Is this normal behaviour or should it be rock steady? if so what do I check next?

Regards,
Chris.
CHRIS_F is offline  
Old 18th Dec 2014, 4:19 pm   #2
peter_sol
Octode
 
Join Date: Aug 2003
Location: Welwyn Garden City, Herts. UK.
Posts: 1,906
Default Re: Technics SL1200 MK2-A

I think you will find that the speed is rock steady.
It is the dots on the platter which vary.
Practically impossible to get perfect they are cast then painted.
peter_sol is offline  
Old 18th Dec 2014, 4:34 pm   #3
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,764
Default Re: Technics SL1200 MK2-A

I'd often wondered this myself. My Technics SL-D2 does the same thing despite cleaning the adjustment pot. My old man used to tell me to get them as still as possible many years ago
PsychMan is offline  
Old 18th Dec 2014, 6:38 pm   #4
sp10mk11
Octode
 
sp10mk11's Avatar
 
Join Date: Feb 2009
Location: Cornwall, UK.
Posts: 1,275
Default Re: Technics SL1200 MK2-A

As Peter has said it is the machining on the platter.

I had quartz lock Denon years ago and it drove me nuts to see a slight movement of the bars. I rang Denon and they guy there explained it is the machining that causes it, even my beloved Technics SP-10 mk11 the speed bars would move fractionally.

I have seen loads of 1200s over the years where the dots wander up and down and back an forth but it matters not.

Gary
sp10mk11 is offline  
Old 19th Dec 2014, 7:29 pm   #5
CHRIS_F
Tetrode
 
CHRIS_F's Avatar
 
Join Date: Apr 2014
Location: Merseyside, UK.
Posts: 57
Default Re: Technics SL1200 MK2-A

Thanks for the replys Guys maybe I am just being too fussy, but I cant help wondering why the manual says calibrate the pitch specifically to 262.08KHz when I can't get a steady reading my meter is fluctuating between 262/263 even dipps down to 261 at one point. My Turntables have been like this for years and i manage to beatmix with them ok and I can't hear any wow and flutter, so maybe I am worried about nothing, but as I am eager to learn about electronics, just wondered if this is something that could be fixed or is it perfectly acceptable? I uploaded two short clips of the problem see below.

https://www.youtube.com/watch?v=dAhZFalyj-k

https://www.youtube.com/watch?v=SJweylk7HxY

Thanks Again,
Chris.
CHRIS_F is offline  
Old 19th Dec 2014, 7:31 pm   #6
Nickthedentist
Dekatron
 
Nickthedentist's Avatar
 
Join Date: Jan 2005
Location: Oxford, UK.
Posts: 17,820
Default Re: Technics SL1200 MK2-A

Does your meter definitely give stable readings when connected to a signal generator? Some don't, particularly if the frequency is in-between two readings, e.g. 262.5 KHz.
Nickthedentist is offline  
Old 19th Dec 2014, 11:11 pm   #7
cmjones01
Nonode
 
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
Default Re: Technics SL1200 MK2-A

Having looked at the video, I really wouldn't worry about what you're seeing. The frequency reading on multimeters like that is nowhere near precise enough to read to five significant figures like the Technics manual specifies. Put another way, the turntable is probably more accurate than the multimeter.

If you want to measure it properly, use a frequency counter with at least 8 digits and a good quality frequency reference.

I've used a different method for setting up my SL1200s. The adjustment is all about getting the analogue action of the pitch fader centred around the quartz-locked centre position. I just adjust VR301 until the turntable gets very slightly faster when the fader is just below the centre (just when the green light goes off) and very slightly slower when the fader is above the centre, just when the light goes off. That makes beat-matching much easier for pitch settings near 0 - it's really annoying to try and nudge the turntable just a bit faster than 0 and have it actually slow down! That's what happens if VR301 isn't set right.

Chris
__________________
What's going on in the workshop? http://martin-jones.com/
cmjones01 is offline  
Old 19th Dec 2014, 11:37 pm   #8
McMurdo
Dekatron
 
McMurdo's Avatar
 
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
Default Re: Technics SL1200 MK2-A

I've calibrated hundreds of these.

Forget the signal generator way of doing it, it's confusing and fiddly.
First of all, check the 'quartz lock' is working. The slide pot is a 2-track affair. One side is a standard carbon pot track, the other forms a switch which only closes when the slider is at the click stop. When this happens, the green quartz lock led should come on and the variable speed function is disabled.

The machining of the strobe dots in the platter is perfect and stable but a CFL or fluorescent lamp will confuse it. You have to view the dots only via the strobe LEDs.

The 2 adjustments are the centre zero pot (on the slider pcb) and the span pot (on the motor pcb).

The problem is that the quartz lock switch can get out of sync with the zero-point calibration, so get this right first. Looking at the calibration strobe marks, rock the slider around the switchpoint and adjust the zero pot so the speed remains steady either side of the centre point and with the green led either on or off. There is a fair amount of dead band when it's right.

Then adjust the span pot under the platter on the main board to get the +6% point right. It's a known issue that the -6% will not always 'come in' when the +6 is ok.

Check the zero point again if the span has to be adjusted.

If the speed fluctuates after this, you've got an electrical problem.
If this is a turntable used by a DJ then expect the slider to be worn as they are usually in constant use. They are available from Panasonic.
__________________
Kevin

Last edited by McMurdo; 19th Dec 2014 at 11:42 pm. Reason: PS my and Chris posts at same time?
McMurdo is offline  
Old 20th Dec 2014, 10:15 am   #9
Restoration73
Nonode
 
Restoration73's Avatar
 
Join Date: Jun 2013
Location: Surbiton, SW London, UK.
Posts: 2,801
Default Re: Technics SL1200 MK2-A

All the above rely on the internal crystal oscillator. Surely the only way to check is to
play a standard test record, e.g. Cardas Audio, and measure the frequency of the 1kHz
bands on side 1.
Restoration73 is offline  
Old 20th Dec 2014, 11:05 am   #10
Amraduk
Hexode
 
Join Date: Jan 2007
Location: Welwyn Garden City, Hertfordshire, UK.
Posts: 453
Default Re: Technics SL1200 MK2-A

The human ear can only detect pitch changes of a certain amount, depending on the frequency of the note. Take A above middle C, that equals 440Hz. The just noticeable difference in pitch that the ear can detect for frequencies below 500Hz is about 3Hz.

If your frequency reading is 263KHz, that would be an error of 1.0035%, which, at 440Hz, would give you 441.55Hz. That is about half of the just noticeable difference of 3Hz, so it would be unlikely that it would be noticeable, unless you have 'perfect pitch'.

Regards,

Dave.
Amraduk is offline  
Old 20th Dec 2014, 8:15 pm   #11
sp10mk11
Octode
 
sp10mk11's Avatar
 
Join Date: Feb 2009
Location: Cornwall, UK.
Posts: 1,275
Default Re: Technics SL1200 MK2-A

These decks have been used for BPM mixing since the 1970s when they were picked up on by clubs (prior to that they were introduced as hi-fi turntables), to use for that purpose they are perfect though often the records used on them are not in terms of speed accuracy, I was mixing DJ in the 1980s and to be honest I never used the strobe for anything, As kevin pointed out getting a flat spot either side of the "0" on the pitch control is far more important, when I think the state some were in that I worked with that "0" set was way out on.
I think because you have got this reading on your meter plus the machining irregularities on the platter has got you chasing a rainbow here............

Gary
sp10mk11 is offline  
Old 21st Dec 2014, 11:29 am   #12
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: Technics SL1200 MK2-A

One way out would be to fit a separate switch for the quartz lock function, then you can use a normal slider without a switch to fix the wear issue, and when you drop the switch out of lock mode, the speed goes to wherever you left the slider.

Not original, but maybe better.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 21st Dec 2014, 1:03 pm   #13
cmjones01
Nonode
 
Join Date: Oct 2008
Location: Warsaw, Poland and Cambridge, UK
Posts: 2,669
Default Re: Technics SL1200 MK2-A

Quote:
Originally Posted by Radio Wrangler View Post
One way out would be to fit a separate switch for the quartz lock function, then you can use a normal slider without a switch to fix the wear issue, and when you drop the switch out of lock mode, the speed goes to wherever you left the slider.
Interestingly, that's what Technics themselves did with the M3D version of the SL1200. They seem to have realised after 20 years or so that keeping the pitch control action monotonic around the centre position was important to DJs!

Chris
__________________
What's going on in the workshop? http://martin-jones.com/
cmjones01 is offline  
Old 29th Dec 2014, 10:28 pm   #14
CHRIS_F
Tetrode
 
CHRIS_F's Avatar
 
Join Date: Apr 2014
Location: Merseyside, UK.
Posts: 57
Default Re: Technics SL1200 MK2-A

Hi guys, thanks for the replies. I noticed something weird last night, as Kevin mentioned the strobe dots rely solely on the led's strobing, but when I was testing my turntables I had a lamp behind me and low and behold it has a ccfl lamp in it, when I tried the turntables in the pitch black I can't see any movement of the strobe dots they seem steady.

I have a couple of questions though, firstly does anyone know if those cheap frequency counters on ebay are any good? or if not where can I get a decent cheap one some have loads of digits but only a a 100hz resolution, am i right in thinking I need a 1hz resolution? I know I don't need a freq counter but I trying to learn electronics as I go as well as getting my turntables in tip top condition.

How can I test if the quartz lock is engaging (led is broke) or where on the pitch board could I bridge or put a switch to test the quartz is engaging at any pitch point like the later 1200's(see below for pitch board pic)

Also I have worked out from the date code and the size of the RCA cutout on the underneath that both my decks are manufactured in 1981, they are also marked as 1200 Mk2-A's which means that the supplement service manual applies to mine but I am a bit confused as to what pitch control should be in them I have heard that many people have had troubles calibrating them no mater how hard they try I only have the supplement manuals not the original service manual, it says replacement pitch fader should be part number "sfdz122n11" but another supplement says sfdz112n12 does anyone know which is the correct one for a 1981 deck after the revision labelled as 1200mk2-a

Thanks again for the help much appreciated,
Chris.
Attached Thumbnails
Click image for larger version

Name:	Pitch.png
Views:	446
Size:	42.9 KB
ID:	102106  
CHRIS_F is offline  
Old 30th Dec 2014, 10:36 am   #15
sp10mk11
Octode
 
sp10mk11's Avatar
 
Join Date: Feb 2009
Location: Cornwall, UK.
Posts: 1,275
Default Re: Technics SL1200 MK2-A

As far as I know the quartz locking is never off, if it were I would think the platter would spin off into oblivion, I have come across cheap direct drive DJ decks that say they are quartz locked but it turns out they are on quartz locked at the fixed speeds (33&45 rpm) beyond that they run on standard servo control.
The beauty of the Technics was that speed control is always under quartz control regardless of its speed giving it is high accuracy so when mixing with it, whatever position you put the pitch control in it will stay at that speed regardless.
I often thought that the tolerances on the pitch controls could have been tighter aswell so this having to set up each one individually for each deck could be avoided.
Gary
sp10mk11 is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 7:12 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.