Systemdek IV E Fault 33RPM

roman around
kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 02 Jul 2019 20:56

Hi Mark,

Thanks for taking the time to pool at the pic of the PCB and giving me your thoughts. I wondering if you or anyone else on the forum would know if that .047k cap would be responsible for controlling the motor speed.

Cheers
Ken

markcass
long player
long player
Great Britain
Posts: 1319
Joined: 26 Oct 2002 23:16
Location: Surrey

Re: Systemdek IV E Fault 33RPM

Post by markcass » 07 Jul 2019 11:17

Hi Ken

Sorry for the delay!

I think the speed will be controlled by a crystal oscillator somewhere on the board. This generates a sine wave that ultimately (via the rest of the electronics) controls the motor speed, just as the AC mains frequency controls the speed of these motors when they are directly connected via a 'passive' power supply.

Mark

Alec124c41
vinyl engineer
vinyl engineer
Canada
Posts: 23141
Joined: 28 Oct 2002 03:24
Location: North of Toronto, Canada

Re: Systemdek IV E Fault 33RPM

Post by Alec124c41 » 07 Jul 2019 15:40

Any component that looks burnt, split, or bulging, should be replaced.

Cheers,
Alec

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 14 Jul 2019 14:41

Thanks all,

Sorry for not getting back sooner....... still trying to sort this problem out. Does anyone know if that .047K capacitor would have anything at all to do with controlling the 33rpm speed. The motor seems to be trying to turn on 33 but doesn't quite make it.

Thanks
Ken

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 14 Jul 2019 22:13

I realise a photo doesn't show everything, but I've attached 2 pics of my PCB. I hoping someone might see something obvious which is stopping the motor from running at 33rpm. I think it has something to do with either the 0.047k capacitor or one of the two crystal oscillators on the right side of the board. This is just my guess but would welcome any suggestions from those on the forum far more experienced. I would also welcome any advice to how this board controls the speed of the motor - I think its frequency but not entirely sure.

Many thanks
Ken

46019

46020

Alec124c41
vinyl engineer
vinyl engineer
Canada
Posts: 23141
Joined: 28 Oct 2002 03:24
Location: North of Toronto, Canada

Re: Systemdek IV E Fault 33RPM

Post by Alec124c41 » 14 Jul 2019 23:20

Some of those solder joints look iffy.

Cheers,
Alec

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 15 Jul 2019 00:55

Alec,

Nearly all are original. Only 4 capacitors were changed.

Cheers
Ken

markcass
long player
long player
Great Britain
Posts: 1319
Joined: 26 Oct 2002 23:16
Location: Surrey

Re: Systemdek IV E Fault 33RPM

Post by markcass » 15 Jul 2019 10:43

I would also welcome any advice to how this board controls the speed of the motor - I think its frequency but not entirely sure.
Yes, it's definitely frequency-controlled. That's the only effective way of altering the speed of an AC synchronous motor, as the speed of rotation is locked to the frequency.

You can make small changes to the platter's speed on certain decks by altering the tilt of the motor mount and/or using a tighter or looser belt.

HTH

Mark

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 15 Jul 2019 18:22

Thanks all,

Does anyone know which components control the 33rpm speed.

Cheers
Ken

markcass
long player
long player
Great Britain
Posts: 1319
Joined: 26 Oct 2002 23:16
Location: Surrey

Re: Systemdek IV E Fault 33RPM

Post by markcass » 15 Jul 2019 18:43

Hi Ken

One of the two crystals must generate the (very high) frequency oscillation, which is then divided down and amplified by the other components to yield the necessary 50Hz AC signal to run the motor at 250 rpm, turning the platter at 33.3 rpm via the belt drive.

I'm afraid my knowledge doesn't extend much further than this, but I suspect the two ICs next to the crystals play a role, one for each frequency/speed. It's difficult from the image to see what they are, but they are connected via sockets so could be changed if one of them is faulty. The other, larger IC, an LM324N, is a package containing four individual op-amps (operational amplifiers).

Have you considered posting over on the Analog Source forum at diyaudio.com? From lurking over there, I suspect there are a number of members who could take one look at the circuit and have a good idea what each component does.

HTH

Mark

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 15 Jul 2019 23:45

Many thanks Mark,

Haven't tried that other site but will do.

Cheers
Ken

kdt6452
junior member
junior member
Great Britain
Posts: 14
Joined: 09 Jun 2019 15:12

Re: Systemdek IV E Fault 33RPM

Post by kdt6452 » 03 Aug 2019 13:18

Good shout Markcass,

The guys at diyaudio diagnosed the fault really quickly. It was one of the IC's. After swopping them around, turntable now working great at 33rpm. Now looking for a replacement m706b1 IC to get the turntable fully operational at both speeds.

Cheers
kdt6452

Geordiejohnh
England
Posts: 1
Joined: 27 Aug 2019 12:20

Re: Systemdek IV E Fault 33RPM

Post by Geordiejohnh » 27 Aug 2019 13:07

Hi Ken,

Glad you're well on the way to Hi-Fi heaven again, and hopefully your solution was a little cheaper than mine.

I took a slightly different route...

I have owned a Systemdek IV E from new, (Walnut) and enjoyed many years of enjoyment until drive issues began.

I took the Deck to my local Hi-fi shop in Gateshead where they replaced the motor, saying that a number of the circuit board components were beyond repair. (That was about 12 years ago).

The new motor worked well, but the soundstage and solidity was never quite the same. (plus increased motor noise).

So around 8 years ago I bit the bullet and purchased the origin Live DC motor / power supply upgrade ....
Best thing I ever did ! :-)

It was really simple to fit and the difference was like chalk and cheese, and from my recollection sounds significantly better that the original Systemdek setup.

4 years ago I also sent the RB300 Arm to Rega for a re-wire, which also brought about sonic improvements.
Apart from the Systemdek IV, the rest of my kit consists of Rega RB300 arm, Rega Exact cartridge, Rega Brio R amp, Rega Apollo CD player, Quad 11L Loudspeakers with Atacama nexus stands.

I still think that the profile and elegance of the of the Systemdek IV takes some beating, the deck has such beautiful lines.

Anyway mate, I wish you many hours of happy listening :-)

John

ps thinking about a cartridge upgrade to the Grado Reference platinum - has anyone any ideas / coments