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Thursday, 2 February 2017

Linn Axis (of evil) repair

Belated happy new year readers!

Been a really busy January, and I've not had much time in the workshop. I've completely moved a radio station for a charity, and it's been stressful! (more on that in a forthcoming post)

Anyway, Jon rang. A fine cycling chap from Bristol. Got an Linn Axis that won't run....

Can you take a look?

Yeah, why not...


It duly arrives sans platter and stylus.

I plug it in , and sure enough the motor just stutters... which is pretty usual for one of these.

The motor drive board will be faulty. Now there's much BS on the interwebs that these boards aren't repairable as "the programmable parts are no longer available" .... which is rubbish, as there aren't any.... someone's probably just trying to flog you an upgrade ... and Linn ownership is all about upgrades , right?

It's just a bunch of logic, and some op-amps...

This board is quite an early one, as it's got a ribbon cable to the speed/on/off switch which is soldered straight into the board...


So. Remove the sub platter and belt. Clean up the inevitable oil spill from the bearing. Now move the turntable to the edge of the bench, and remove the three large suspension screws holding the top plate to the rubber suspension mounts. If you're doing this with the arm attached, remove the cable strain relief first. Lift up the front edge of the top plate a bit and have a peep underneath. If your switch is attached by a coloured ribbon cable, then you'll need to pop the switch out, and slide it back inside. If it's a copper coloured flexi, (like Jon's below) just disconnect it from the motor drive board. Lift the top plate clear and put it out of reach of the cat.


Now remove the 6 small screws indicated by the red arrows, and the mains lead from the terminal block on the bottom right.

With a bit of jiggling, you should now be able to extract the board. You may need to squash one of the suspension mounts a bit to extract it.






Now change every last damn electrolytic on the board, even the high voltage ones.

Here's the shopping list:
2 x 33uF 350V axial
2 x 47uF 250V axial
2x 220uF 16V axial
7x 22uF 50V radial.





Now a word of warning.... this board is "live" when it's connected. So use an isolation transformer when doing any fault finding on it. With a bit of luck, you should now have a running board.. however, I have seen turntables with D2 & D3 open circuit, BR1 short circuit. A real head scratcher was one which intermittently blew fuses, which was one of the BUX85F output transistors!

Now if you switch the motor on without a platter and belt on, it will spin up, and then stall a few seconds later. This is usual. Once the platter is on, it should work fine.

.... of course Jon's wasn't going to be so easy, and also needed an LM324 quad op-amp replaced to finally restore operation....

I've seen forum posts saying just change the small caps....... change 'em all. These had been in there since 1989 and were shot away!











Once it's all happy, put the top plate back on, do up the suspension screws (not too tight) and replace the strain-relief on the tone arm wires and check the speed (you really need the top platter on when doing this)

Speed is adjusted using an INSULATED screw driver through two holes on the underside. They have bungs in them, you'll need to just pop those out, and replace them once happy.


Now Jon ... where's your stylus?

UPDATE March 2019! ...

Colin's just popped round with another Axis with a common problem after recapping .... motor spins backwards or not at all or just sits there vibrating. Usual causes are the two HEF4013 flip-flops hanging a line up. Change 'em both. They're just by the switch cable, and are U1 and U2.

Other frequent flyers are the two watty 15K resistors, R2 & R3. With these faulty, there won't be 35V across C5.

Have fun all!



11 comments:

  1. Welcome back Mr D! We missed you.
    Not much to say here, excellent article and all is needed is a decent MC cartridge. Much fun reading, thank you.

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  2. Hi Mr D,
    I belonged to an after school electronics club circa 1981 building projects from etched PCB's following projects within 'Everyday Electronics'magazine and thoroughly enjoyed these.

    I have always been interested in HI-Fi and have owned Linn & Naim equipment up until a divorce in 2010 put paid to this.
    I recently bought a 1987 Linn Axis turntable that would not run but following you blog, I changed the capacitors (only High Voltage ones) and it is now running like new!
    thank you ever so much - I really want to get more involved with such upgrades and look forward to further blogs and info via your website.
    Best regards,
    Geoff

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  3. HiYa Doz,

    I've had my Axis from new since the late 80'5 after upgrading from a Rega Planar 3. A few years ago I swapped my Axis with my Dad, who had a Sondek. His hearing was going (actually turned out to be dementia) so he thought I'd appreciate the Sondek and he was fine with the Axis. My Dad died from Dementia two months ago and weirdly the Axis (which I got back after my parents was sold) developed the speed fault at the same time. Partly sentimental and partly 'cos it's an awesome deck I followed your advice and replaced all the electrolytics. Worked first time and she's rocking again! Speed tested and after a bit of tweaking back at spot on 33.333. Dude, good job! Last time I wielded a decent soldering iron in anger was my 'A' level electronics project when I was 18, I'm now 56. If I can do it, so can anyone. So, great blog, great advice. Dad would be happy. Cheers, Steve

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  4. Followed your instructions and my Axis is alive again. The only "issue" is that when switching to 45 it takes about 10 seconds before the speed change happens. Is this normal?

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    Replies
    1. That's not normal :( Should be pretty much instantaneous... before diving into the electronics... is the belt ok?

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    2. It's a new belt. It continues to turn at 33 once the green light comes on and after 10 seconds you can see a sudden acceleration and it moves to 45. Once up to speed it works perfectly. I replaced the 4 high voltage capacitors first and noticed this issue when testing. I then removed the board again and replaced the other 9 capacitors and still the same. It's not a big problem as it won't be used for 45s but thought I'd share the experience.

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  5. Andy, I wonder if you can help me please. I just reassembled my Linn Axis, which has been boxed for 17 years. I bought a new Thakker belt, turn it on an hey, no, no, no! The speed is irregular and there appears to be a bit of a scraping sound as it turns. If I life the spindle, twist and replace it, then the sound goes away temporarily, which suggest an oil issue. This does not explain the irregular speed though. I found a 2011 Aussie article https://www.stereo.net.au/forums/topic/33726-linn-axis-speed-problem-fix/ that talks about changing capacitors in a similar manner that you did. The only problem is that I dont know who to turn to for a fix, because I'm not an electronics buff - would you take a look at it for me please? I spoke with a Linn specialist who told me "they don't make the parts any more, we can cannabalise it for parts and transfer them on to an old LP12 chassis - I ain't got that sort of money to spare unfortunately! Thanks for reading this.

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    Replies
    1. If it's a scraping sound, it's most likely your motor is toast. It's only a 120V Premotec motor, I'd start by changing that first. Buy a motor online, not Linn's inflated prices. For some reason I hear the "the parts aren't available" line very often. I'll say it again... EVERY SINGLE PART IS STILL AVAILABLE, NEW, TODAY! I'm not in a position to take on repair work at present. Perhaps you have a local TV repair place that you could take it too, and show them this article?

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  6. Great response - thank you. I guess your father would be proud and happy that his turntable is still bringing happiness.....
    Regards,
    Geoff

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  7. I have replaced all of the caps on my Axis board, only to find after 6 months I had the same problem again. Replaced the board with a new Hercules 2 board - an easy fix / upgrade care of Stamford Audio. My Linn Axis is like a new bunny and playing vinyl like out of the box new......….

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