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
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
Attachments
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.
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.
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
BTW the images are very clear on my monitor.......... is there something up with yours.
Thanks for your help
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).
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).
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.
Also, find another tech.
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
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
I wouldn't like to give a definitive answer to that although you could say the lower frequency crystal would be used to derive the slowest speed... but it doesn't necessarily work like that as it depends on the division ratios available and how the raw frequencies divide down.
Surprising to see the 4.443619 MHz crystal used here (actually its 4.3361875 and is the colour subcarrier frequency of the old PAL TV system).
Although crystals are normally pretty (make that very) reliable they occasionally can give problems.
Just swap them over as Arch suggested or you could (if they are identical) swap the chips.
Edit... reply was in response to kdt's above.
Surprising to see the 4.443619 MHz crystal used here (actually its 4.3361875 and is the colour subcarrier frequency of the old PAL TV system).
Although crystals are normally pretty (make that very) reliable they occasionally can give problems.
Just swap them over as Arch suggested or you could (if they are identical) swap the chips.
Edit... reply was in response to kdt's above.
that sounds reasonable.
...... and use a thin blade screwdriver to gently lever the IC out of the socket a little at a time.
Lift each end a little in turn... if you try and do it in one go then it will suddenly come free stabbing you in the fingers with its pins, and also bending the pins badly.
Make sure you know which way around they go before beginning.
We need some action with with this
not just keep talking about it.
It takes less time to remove an IC than it took to type this one sentence... and I'm pretty quick on a keyboard. Do it, see what happens. If they are the same device number then swap them around.
Lift each end a little in turn... if you try and do it in one go then it will suddenly come free stabbing you in the fingers with its pins, and also bending the pins badly.
Make sure you know which way around they go before beginning.
We need some action with with this
not just keep talking about it. It takes less time to remove an IC than it took to type this one sentence... and I'm pretty quick on a keyboard. Do it, see what happens. If they are the same device number then swap them around.
Hi Guys,
I've swopped the IC M706B1 chips around and the problem reverses. ie, the motor turns at 33 instead of the 45 setting. I'm assuming that means one of the chips has gone and everything else is ok. I'm can't check to see if the speed is correct at either setting until I put everything back together. But the problem does reverse when I swap these chips around.
Cheers
kdt6452
I've swopped the IC M706B1 chips around and the problem reverses. ie, the motor turns at 33 instead of the 45 setting. I'm assuming that means one of the chips has gone and everything else is ok. I'm can't check to see if the speed is correct at either setting until I put everything back together. But the problem does reverse when I swap these chips around.
Cheers
kdt6452
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