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
6x 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?

1 comment:

  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.