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| Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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3rd Oct 2017, 8:34 pm
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#1 |
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Heptode
Join Date: Nov 2008
Location: North Walsham, Norfolk, UK.
Posts: 900
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Anyone know how this works ? Akai DD Deck
Evening all. Been fiddling with this deck, it came to me running slow, when I removed the bottom I found all the presets cranked right round to one end so I proceeded to set up the off set voltage & torgue balance using a scope as per the manual, that stopped it varying speed wise but I still can't get enough speed out of it, both 33 and 45 are running roughly the same amount slow with both pots and the front speed pot on maximum but I don't know how this bit of the circuit works. I have enclosed the circuit diagram in the hope that someone with experience of servo's might be able to point me in the right direction or explain simply how it works.
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3rd Oct 2017, 9:23 pm
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#2 |
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Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,960
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Re: Anyone know how this works ? Akai DD Deck
Is the speed reference voltage provided by zener diode D1 correct at 5.4V?
Integrating capacitor C6 0.25uF is a possible cause of the speed problem. This generates a ramp that is compared with the desired speed voltage set by the speed pots. Ron Last edited by ronbryan; 3rd Oct 2017 at 9:38 pm. |
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3rd Oct 2017, 10:33 pm
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#3 |
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Octode
Join Date: Jan 2003
Location: Guildford, Surrey, UK.
Posts: 1,960
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Re: Anyone know how this works ? Akai DD Deck
Apologies, C6 is 0.47uF, not as I wrote earlier.
Ron |
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4th Oct 2017, 9:20 am
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#4 |
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Octode
Join Date: May 2011
Location: Lancashire, UK.
Posts: 1,351
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Re: Anyone know how this works ? Akai DD Deck
Is the pitch control centred correctly (and working correctly) ?
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4th Oct 2017, 10:26 am
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#5 |
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Heptode
Join Date: Nov 2008
Location: North Walsham, Norfolk, UK.
Posts: 900
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Re: Anyone know how this works ? Akai DD Deck
Cheers for the pointers Ron Bryan, Zener supplying 5.4 volts, O.47 cap checked reads ok, changed to 1 mf (didn't have a .47) deck then runs slower. Mooly, all pots including pitch read fine. checked R8, R9, R10, R11 R13, R14 all within tolerance, + & - supply lines about a volt low Hmm back to basics check the smoothing caps C22 reads as 6800r resistor and C21 a 400 Mf so changed em both and guess what, running fast now
 just got to set the torgue and balance again and we should be ok as it's now pulsing a bit especially on 33 seems I shouldn't have been scared of the servo and should have checked the basics, as an engineer I worked with once said always check the supply lines before you do anything else. Very wise advice. Perhaps I should have listened to him lol
Last edited by nigelr2000; 4th Oct 2017 at 10:27 am. Reason: spelling |
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4th Oct 2017, 8:06 pm
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#6 |
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Octode
Join Date: May 2011
Location: Lancashire, UK.
Posts: 1,351
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Re: Anyone know how this works ? Akai DD Deck
That's great. Pleased to hear you have found the trouble.
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4th Oct 2017, 8:12 pm
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#7 |
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Rest in Peace
Join Date: May 2003
Location: Harlaxton, Lincolnshire, UK.
Posts: 3,944
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Re: Anyone know how this works ? Akai DD Deck
Hi Nigel
Now that you have found the fault put the original C6 back (0.47uF) if you haven't already done so. |
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5th Oct 2017, 9:37 am
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#8 |
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Heptode
Join Date: Nov 2008
Location: North Walsham, Norfolk, UK.
Posts: 900
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Re: Anyone know how this works ? Akai DD Deck
Did that after trying a 1 mf thanks Colin
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6th Oct 2017, 1:15 pm
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#9 |
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Octode
Join Date: Feb 2009
Location: Cornwall, UK.
Posts: 1,275
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Re: Anyone know how this works ? Akai DD Deck
I cannot help you much but years ago I had this deck with the same problem, I ended up changing some resistors around the pre-set speed controls to bring it back up to speed, I am sorry I cannot tell you any more
Good luck Gary |
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