Repairing Linn Axis Motor Drive Amplifier

Ancient thread revival!

I'm hoping someone can point me in the right direction. I'm repairing a Linn Axis. I've replaced all the electrolytics and also the bridge rectifier. The motor now runs, but only when you help it by hand. Measuring the voltage input to the motor, it only seems to be getting the 70vac feed for a split second and then drops to around 25vac, which in itself seems a touch low. I'm completely stumped :( Any thoughts you could offer would be great!
 
The circuit is designed to go into quiet mode which is around 25VAC but should only do that once the platter is up to stable speed. The circuit will only operate properly with the platter on. It should stay at the higher voltage until the platter is up to speed. I've attached a copy of the schematic in case you don't already have it.
 

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I've nailed it down to the motor not getting the initial 70vac "start-up". Switch it on and goes straight 25vac. Any idea what gives it that initial burst? So far I've changed all the lytics, bridge rectifier, R2 and R3. I have a feeling the issue lies around U4, but before I try and remove that, a bit of direction would be helpful.
 
I think I didn't complete a previous attemot to post (phone challenges), and someone else explained the startup/running voltage behavior so I didn't follow up.

I had one with startup problems and found a power resistor (don't recall if it was metal oxide film or that's what I replaced it with) that had fractured but the two halves were still touching. In the dark with the platter removed I could see an orange glow where the separated resistor halves touched.

I couldn't believe it still ran like that once I manually assisted the platter rotation.

I was able to replace it from the top side with the leads precut for minimal protrusion through the circuit board. I didn't want to get the board completely out if I didn't need to.
 
So are you actually measuring 25VAC 50Hz on both legs of the motor? If you are then U4 should be fine. U4 is the output driver to the motor. I would check the two Quad Bilateral Switch chips U6 & U7 and see if any of the switches have shorted open.

I believe the circuit fires up at about 70VAC and then a feedback loop opens to drop the voltage down to around 25VAC. If it's starts at 25VAC then the feedback loop must be stuck open suggesting that one of the switches has shorted.

Make sure C6 and C11 are ok. They are the coupling capacitors for the for U4's input. If they have dried then their reactance will go way up for the 50Hz signal and you won't get enough input drive.
 
Hi Peter, I admitted defeat in the end. I narrowed it down to the feedback section of the circuit and changed out u6 and u7, but still no joy. As far as I can tell everything is/was in spec and continuity throughout the circuit. It's both annoyed and baffled me in equal measure. It still runs and runs well, just needs a push start.

When you say transformer, what exactly are you talking about? The Axis doesn't have a transformer!
 
Thanks. I'll change all the electrolytics.

Someone recommended changing the R1 to a varistor; is this worth doing?
Also, I notice there are two large resistors labelled "273-0 15k 5%" Do these carry much power; if so is it worth changing them as well?

The bridge rectifier is working now; any advantage changing this?


This post is 4 years old, but I need some help.
Do you recommend changing the large resistors? They get very hot.
Is there a more effective replacement that can reduce the heat? Or other specs for replacing these resistors?

Carlos


Sent from my iPad using Tapatalk
 
Just an update on the above collective wisdom...

Rx'd the turn table n behalf after it had been 'serviced' and someone. They had followed the above general advice and replaced the power supply and more esp the drive capacitors.

Problem #1:
I repaired the momentary switch that was 100 - 1k ohms as someone had melted with 'contact cleaner' that melted the moving rocker part of the switch perfectly onto the piano wire moving contact. Solved problem #1 = Erratic starting.

Problem #2 As above seemed to be chasing my tail trying to 'make it work' with no mechanical load. The AC drive seemes to boot as per above discussion at max power (Motor almost audible if you listen very carefully) and then 'drops back. With NO PLATTER and or belt drive it seems to 'throttle off and sop / stall. With platter fitted it runs !!! So don't forget to just try this out...

On provisional soak test at present with mag cartridge output into some amplified PC speakers and wife's 1970's 33 and 45 record collection spinning up.

Will confirm result after a few days running... Stand By

Recommendation:
Yes the AC and bleed / dropper resistors sit there warm / hot all the time so suggest you would improve life of the system by powering off at wall. Or get someone to add a respectable ON:OFF AC switch ?

~ Andrew
 
I am looking for a test review with measuring results of Linn AXIS or of this motor control board - go to
Pink Triangle LPT PSU pcb - Vinyl Engine
At best in the same kind than this measurements of LP12:
Linn LP Playing System Measurements | Stereophile.com
Who know, where I find this?

In opposite to the Lingo versions there are no quartz oszillators in use. What means this for the sound quality in cases, where the AXIS motor control unit was in use in an outdoor housing for the LP12 ?
Any experiences in this matter?
In this case also this thread is of interest:
http://www.diyaudio.com/forums/anal...ve-vs-sine-wave-oscillator-motor-control.html
 
Question about voltages

Not activities for time at this thread but try ask a question.

Meant that 320V voltage dropped by half when motor starts running?
13V is stable at my AxisPSU
Motor voltages are different for pins. Other drops about 11V and other is normal(25V). Probably same problem is starting voltages too.
 
First post. Just fixed a friends Linn Axis PSU that was running slow. Changed all the caps just in case, no change. Put a scope ( battery powered ) on it and found that the waveforms at O1 and O2 looked strange and not the same also at 30HZ. Changed the U3 oscillator op amp and it seems good now, two clean sine waves 90 degrees off and at about 50HZ for 33.3rpm. Note for info: 24 pole motor at 50HZ = ((2/24poles) * 50hz) * 60sec = 250rpm. A 21mm motor pulley / 160mm platter pulley = 0.13125 * 250 = 32.8rpm.
 
My Linn Axis is working again

Hi all,
As i said if I managed to fix the Axis motor board I would post accordingly, so here goes.
FIRST A WARNING, the motor board is connected directly to the mains supply so will need VERY careful handling if you are not to give yourself some unpleasant surprises.
Remember electricity will not give you a second chance and until the fuse blows Battersea Power Station or its equivalent is sitting at the other end of the cable. Also any test equipment that is connected to this circuit will be "live", so earthed equipment (scopes etc) MUST either have the earth wire lifted from the plugtop or not used at all. If you have any doubts about your capabilities do not work on this board.
There is a way around it and that is to use an isolating transormer and then you can earth the secondary but it is somewhat a costly exercise.
Also remember the "one hand in the trouser/skirt pocket" rule when using test equipment to measure voltages etc
So..........
My unit would not turn the motor, so first check was voltages on the bridge rectifier, about 320V DC, correct, and also across C5 about 12-13VDC, correct, so I initially suspected the two main coupling capacitors C8/C9, which were removed, measured (both read 33µF, correct value) and substituted for good measure. No improvement of course.
I then turned my attention to the other other electrolytic capacitors C6,C11,C16,and C17. These are all 22µF/63V capacitors and they all measured very low capacity generally 5-6µF. Replacement appeared to effect a total cure, however I was somewhat puzzled when I looked at the sine wave feeding the motor to see it drop in level and the motor stop rotating.
I then remembered Linn's penchant for reducing motor volts so it just turns the platter, the motor relying on the inertia of the platter to keep the motor rotating and vice versa. Once assembled totally all worked fine, with speed being fractionally fast to overcome stylus drag etc, however the speed adjust controls are available through the base of the case if required.
I reckon that the electrolytic capacitors dried out over the years 'til they reached the point of no return and I think that the best solution is to replace them all with new.
Hope this helps you all out there but if you have any further problems send me a pm with phone nr etc and I will try to assist

John Caswell





Thankyou very much John Caswell. My Axis is running again after changing the small capacitors C6, C11, ... How sweet it is to listen to the old records.


Lennart Fransson, Sweden.
 
My 1.5 Linn Axis tables (one working, one flooded & ‘cooked’) have been in boxes for 15-17? years, so I am going to ask a question below based on not having seen one in a long time). I haven’t completely discarded the idea of out-rigging a drive for the damaged one since it needs a base/plinth anyway.

One of the last posts (Snarvax) discussed the frequency of the motor drive.

IIRC, this table changes between 33-1/3 and 45 rpm electronically (only one pulley diameter). I had/have other tables with two pulleys and one had to manually transfer the belt...so I’m just trying to clean that distraction from my mind.

1) Do I understand correctly the motor expects 50 Hz and based on the quadrature drive (sin/cos 90 degree phase shift), might have been a ‘conventional’ capacitor-start motor? Or I’m wrong...it is a motor type that will run over a range of frequencies (I forget which kind if
motor only runs at its design freq...synchronous?

2) Is the 45 rpm obtained by generation of a different frequency (in 33.33/45 or 45/33.33 ratio)?

Thank you
 
1)Do I understand correctly the motor expects 50 Hz and based on the quadrature drive (sin/cos 90 degree phase shift)...synchronous?
The supplied on-board motor is of a similar specification to this or the 110V AC version of this.

2) Is the 45 rpm obtained by generation of a different frequency (in 33.33/45 or 45/33.33 ratio)?
Yes - 67.5Hz.

Good Luck!
 
I still miss a circuit description in detail (schematic as pdf file under post #42).
 

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