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Systemdek iv 33 rpm motor fault
Systemdek iv 33 rpm motor fault
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Old 21st July 2019, 12:16 AM   #1
Kdt6452 is offline Kdt6452
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Default Systemdek iv 33 rpm motor fault

Hi All,

One of the guys over at the vinyl engine forum suggested I try this forum to get help fixing my Systemdek iv E turntable which I had recently got out of storage. Unfortunately when I went to play some of my old records the motor on 33 rpm stopped after about an hour. The motor still plays at the 45 speed but the 33 speed won't. I realize it's not easy suggesting what could be wrong from looking at a picture but I'd be grateful if anyone could take a look at the attachments and make any suggestions as to the possible fault in the PCB which is stopping the motor running at the 33 speed.

I'm not entirely sure, but I think it could be one of the two m706b1 chips next to the 0.22 k 250v capacitor I'm also not sure which one controls the motor speed at 33rpm.

Any help would be appreciated and if you could also confirm if I'm correct in thinking that the 0.047 K 250 capacitor looks damaged and a replacement would be a 47 picofarad polypropylene film capacitor. I'm not certain if the "K" on these old capacitors signified 10% tolerance or 1000 times the stamped capacitor value.

Many thanks
Ken
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File Type: jpg IMG_20190713_185410.jpg (493.6 KB, 69 views)
File Type: jpg IMG_20190713_191144.jpg (847.7 KB, 68 views)
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Old 21st July 2019, 02:52 AM   #2
wiseoldtech is offline wiseoldtech  United States
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Having sold and serviced audio (bench technician) for decades, in all honesty, I have to say this......
While the internet is a wonderful new thing, it cannot provide you with much information regarding a specific issue with a complex electronic circuit board.
Even I, as a seasoned old tech, cannot diagnose your problem across a screen, even with dark blurry and useless photos.
Because ANYthing could be the problem, and I'd have to have it right in front of me, with my magical probes of my test equipment right on the board, then diagnosis would be easy.

In other words, I, and I'm sure others, can do nothing more than specualate, carry on an endless thread about it, which to me is utter nonsense and a waste of time.

Your best bet is to enlist the services of a qualifed, reputable, audio service tech.


By the way, those guys over at vinylengine give me gas - most are a bunch of nitwits with too much time on their hands.
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Old 21st July 2019, 12:25 PM   #3
Kdt6452 is offline Kdt6452
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fyi..... I've taken the turntable into a " qualified, reputable, audio service tech" who charged me to replace capacitors but then told me the motor was done. However, someone else tested the motor and it's apparently. Two different audio service tech's two different magic probes two different answers, two separate invoices but still not working.

BTW the images are very clear on my monitor.......... is there something up with yours.

Thanks for your help
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Old 21st July 2019, 01:13 PM   #4
lohk is offline lohk  Europe
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Your images are indeed dark and blurry, there is very chance to examine the circuit properly. The mentioned capacitor looks blackend, but not because it is damaged but maybe the adjacent electrolytic capacitor is damaged.
You see, there are many possibilities what could have happened with your circuit.

A few things may also be helpful:
The fact that the machine consistenly (?) run with 45 (in the right direction!) shows that the motor is probably not damaged.
The fact that the fault only came up after one hour shows that there is one or several parts failing, which probably might be capacitors, since they fail with age. That may be connected with the power supply, making parts of the circuit not working properly.

All that and much more can be easily measured by a qualified technician who really understands how this circuit works.

Please state which capacitors have been changed already.
Can you do some measurements by yourself using a multimeter or an oscilloscope?
Please be careful since the circuit bears mains voltage.

As a (maybe temporary) solution you can substitute the circuit alltogether by using the classical setting with one resistor and one capacitor as a phase shift for the synchronous motor. As far as I remember (an I have been selling these turntables in the 80ies) the Systemdek was also available without the electronic control (for a single speed).
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Old 21st July 2019, 01:24 PM   #5
audiopro is offline audiopro  Canada
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That one cap is probably okay, but it is not 47p it is 0.047ufd. Also it looks like they replaced one of the axial caps, but not the one near that 0.047 cap. I'd replace that one as well just as a matter of preventative maintenance. And don't use cheap Jackson caps. Those are crap and will fail.
Also, find another tech.
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Old 21st July 2019, 01:31 PM   #6
Kdt6452 is offline Kdt6452
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Thanks for the replies.
I can take some measurements myself if directed what to look for.

Here's another pic which is hopefully clearer and with the changed capacitors
marked in red.

I would just like to get an idea of what may be wrong so that I don't get the run around anymore.

Cheers
kdt6452
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Old 21st July 2019, 01:36 PM   #7
Mooly is offline Mooly  United Kingdom
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Systemdek iv 33 rpm motor fault
Images are extremely clear for me as well.

Do we have a circuit diagram of this thing? as that might tell us much about where the issue might lie.
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Old 21st July 2019, 01:38 PM   #8
Kdt6452 is offline Kdt6452
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Sorry,

Here's the pic
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Old 21st July 2019, 02:02 PM   #9
Arch Stanton is offline Arch Stanton  France
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You have two oscillators, one for each speed I suppose. You can try to swap the two quartz an see if the 45 rpm become 33. It'll give an idea.
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Old 21st July 2019, 02:10 PM   #10
Kdt6452 is offline Kdt6452
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Yes, 2 oscillators - here's a pic of them if that helps. Anyone know which one is likely to be the 33 rpm

Cheers
kdt6452
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