First, I apologize to those who may find this guide a bit basic, rough or incomplete, and those who may consider some of the things I describe as undesirable or misguided. Apologies also for any use of wrong vocabulary; I am a novice, but I hope the meaning is clear. I don't recommend you attempt this if you are unsure and I certainly don't suggest this is the 'proper' way to do anything. If you have any doubts, don't, take your equipment to a professional for assistance. I've used this as a learning process as much as anything.
Secondly, there are many who have advised simply presetting the AS on these arms to some middle value, which should be adequate for most applications. I'm not disputing that, my difficulty was that the AS belt broke with zero bias set, and so I have to get inside the arm to be able to do anything. All I can say is this worked for me.
With big thanks to Tarrant for his advice on how to start I've tackled the job and managed to replace the anti skate belt. Many thanks also to all those who guided me to additional material on the web, that has helped orientate my thinking and allowed be to proceed with more confidence than otherwise. Since I only wanted to replace the AS belt, I only took apart those components that were in the path of that objective. I was lucky in that I did not have to rebuild the bearings in any way, nor did I attempt to rewire the arm, although soldering up the connections on the external arm wire plug to complete the job was something of a challenge; partly because the wires were so short and partly because my eyesight is going the same way these days. I did say I would make an attempt to share the experience, so for those who may be interested, read on:
I needed, by the end of the exercise, to accumulate the following to be able to complete the job:
- A sq. metre of work surface
- Fine soldering iron & high silver content solder
- Good light
- Magnifying glass
- Jeweler's Loupe
- Round tipped pliers
- Standard pliers
- A file
- Fine (watchmaker's) tweezers
- Sticky tape
- Large adjustable spanner
- A collection of mugs!
- Jeweler's screwdrivers
- Epoxy adhesive
I removed the arm from the baseboard by undoing the large hex nut on the underside of the plinth. Before doing so, I stuck a six inch length of masking tape to the top side of the plinth with one edge aligned with the straight section of the curved arm, to allow me to put the arm back in the same position on completion. There was no washer of any sort under the hex nut, so the underside of the plinth was already marked by the rotated nut. The arm is then lifted from the plinth by threading the external cable off the nut, through the hole in the plinth and the arm spacer is then also removed from the cable.
I naively started by removing the three screws from under the anti skate (AS) housing, one of which holds the AS dial in place and instantly realized that more was required to take things apart. The three screw holes can be seen on the underside of part 4 in the following photo:
Part 1 is the plastic cable plug which fits into the collar (Part 2) and connects the external cable to the internal arm wiring. 3 & 4 are actually one piece and this is the housing that contains the bearings and the magnets that provide the AS bias (more later). Part 5 is the top of the AS housing that you look at when you view the arm in place on the plinth.
Start by removing the two grub screws in the collar that retains the cable plug.
As you remove the screws, be very careful not to let the plug twist or pull out, the arm wiring behind the plug is extremely fine and in my case, extremely short, so there is little slack to allow the plug to be removed and set down on the work surface. Note the earth tag fitted to the ground connection, which I presume is intended to earth the arm components. MAKE A CAREFUL NOTE of which wires go where. I had six wires, including two black (earth). One was commoned with the blue and the other ran to the pin with the earth tab. Un-soldering the leads was reasonably easy, but in my arm, it appeared someone had been here before.
Once the cable plug is disconnected, the lower bearing in the arm can be seen inside the collar and housing.
The collar can then be removed by unscrewing, and may need some effort in case the thread has had any locking compound applied to it.
I then marked the screw slots of the bearing adjustment on the end of the housing to give me a reference for re-assembly. Having completed the work it looks as though the inner ring is the lock ring and the outer ring is to adjust the bearing. These slots are where the tip of my round nosed pliers fit to help undo the bearing. If I'd had proper tools, doubtless undoing the locking ring would have been easy, but as I gently applied pressure to undo the ring, both rings turned together and unscrewed as one. I would be careful if you have this difficulty, because if the rings are locked together tightly, if may be possible to damage the thread on the vertical spindle of the arm. As the bearing is loosened, then parts 3 & 4 are able to move away from part 5.
I thought that I might be able to just loosen the bearing sufficiently to fit a new belt and tighten everything up again, but with hindsight, it did all need to come apart. Once undone, the housing can be lifted from the arm base. I recommend keeping the spindle of the arm vertical so that all the bearing components are still in the correct place respective to one and other until you can take a careful look inside at everything. You can see the bearing inner race still in place in the photo below:
If the inner race is carefully removed (tweezers) you can see the bearing cage, which has an 'open' and a 'closed' side (closed side uppermost here). Make a note to put it back the same way, although I had no real need to remove it.
Removed components below:
Left on the spindle of the arm next to the broken belt in the AS housing is the AS adjustment collar and magnets:
The collar may be carefully removed and you will notice a helical groove on it's inner surface:
This groove mates with the slanted dog on the ring magnet, which is able to slide up and down the spindle and vary the AS force. When the collar is mated with the ring, rotating the collar (via the belt, when replaced) raises the moving magnet closer to the fixed one and hence increases the bias.
I managed to get hold of a belt (based on suspected dimensions posted by others) here:
https://sdp-si.com/eStore/PartDetail.as ... roupID=342
You'll notice the small differences between the old belt and the new. The new belt is slightly narrower, and the height of the belt is less (back to tip of tooth). The new belt also turns out to be slightly too long and so some form of spacer is required to tension the belt slightly. This is also important, since the original belt filled the clearance between the teeth on the AS collar and the adjustment screw and the cast AS housing, and effectively prevented the belt from 'jumping' teeth.
A test fit of the belt showed good meshing of the teeth, but also demonstrates that there is some slack to be accommodated.
I made a 'spacer' by clipping a short length of wire coat hanger and folding it as shown. In practice, it is better to do the folding prior to cutting the short length off the wire, easier to handle. A bit of careful filing is then required to ensure that the spacer is the same height as the interior of the housing and there are no rough edges. The small spacer shown was too small, the larger one was almost too big, but it worked for me:
You need to test fit the spacer to find the right location inside the AS housing, where the belt is sufficiently tensioned, but the teeth don't interfere with any internal mouldings or lugs in the housing. The location shown here seemed to work best for me. Make sure that the contact points of where the belt will run on the spacer are 'true' i.e. vertical to the side of the housing to ensure the belt also runs true, although once re-assembled, there is not really any space for the belt to run anywhere else.
The spacer needs to be carefully glued into place ensuring that no adhesive migrates into the path of where the belt will be fitted. I bought some silicone grease to put a small wipe on the back of the belt when fitted, to help lubricate it over the spacer, but it didn't seem required in the end. The belt can then be fitted, but take care to make sure that the AS adjustment collar is turned to place the moving magnet furthest from the fixed magnet, and that the adjustment dial, when inserted through the AS housing (part 5) is effectively set to 'zero'. Careful inspection will show that there is a small lug on the housing that engages with a groove under the dial which contains a 'stop' to prevent the dial being turned to less than zero. The aim is to have the dial read zero when the magnets are furthest apart and hence the bias force is zero.
Check the operation of the belt and then it's just a case of putting it all back together :lol:
A few more tips that may be helpful:
I wrapped a small strip of paper around the arm wires to make it easier to thread them back through all the removed components.
I was able to re-install the bearing adjuster and locking collar as one again, although the firmness of adjustment was not as tight as when I took everything apart. I used the marks I had made on the housing as a reference but tested the adjustment by holding up the arm with the arm tube in a vertical position and giving it a small swing side to side. The bearing needs to be adjusted to the point where the arm tube swings very freely under gravity with no discernible damping from friction in the bearing due to it being too tight. Before replacing the cable plug collar, for my own peace of mind, I put a small dab of clear nail varnish on the bearing locking ring, next to the spindle, since I felt that the combined lock and adjusting rings moved a little too freely. I never did manage to separate the two while I had them removed.
Finally, the hardest bit of all for me was soldering up the arm leads to the cable plug. I can understand why many recommend rewiring at the same time. It would give you plenty of wire to determine your own arrangement for float in the wire length and would give you the chance to work on soldering new wires, always easier than working with old. Because my wires were so short I needed more hands than two people could provide to hold everything in place for soldering. I ended up taping all of the different components to a collection of mugs and using a magnifying glass to give me two free hands to make the solder joints. Good tinning of the connections is a must to allow acceptable joints to be made neatly and quickly without putting too much heat into the wire and burning off the insulation. help here if required: http://www.teamnovak.com/tech_info/how_ ... index.html
Here is my ramshackle arrangement:
Re-solder the wires according to the notes you made on dis-assembly and remember to include the earth tag to contact the plug collar on refitting. The final steps then are to refit the cable plug (be careful not to twist it as you fit to the arm or you might break some of the wires you have just soldered) and the grub screws to hold it in place, and to mount the arm back on the plinth using the tape applied to the top surface to get the alignment right, remembering to thread the spacer, plinth and lock nut in the right order.
Tada! I was lucky. I connected my deck up and everything worked fine first time. Now....... what am I going to do to test that sensitivity and adjustment of my VTA :roll: