Technics tonearm rewire - not for the faint hearted

[worrasf]

First off I acknowledge and give thanks to AoS member 6L6 (Jim) for his excellent post https://theartofsound.net/forum/show...165#post462165

I am currently refurbing an old SL1210. The aim is to have it looking almost as it left the factory and so I'm restricting the mods to those that don't obviously alter the visual appearance. The plinth/top plate has gone off to be powder coated and screen printing for the logos etc. I'll be fitting a new OEM bearing but with a KAB Delrin thrust plate and support wax. I'm changing the PSU to a modern toroidal one with new PCB but keeping it onboard. I've taken the opportunity to swap out the old LED's and microswitches for new ones and lubed cams and springs.

Even though I have a Jelco TK850s sitting in a box I've decided to go with the original Technics arm. Not a huge amount I can do here but am fitting a fluid damper and will run the tonearm wires to a KAB jack plate on the outside of the chassis to enable for plugging and unplugging RCA terminated tonearm leads and avoid a soldered connection at the standard PCB. Which leads me to the purpose of this post - namely rewiring the tonearm. I should say I have never done this before and having completed it there is no doubt it's the most taxing bit of HiFi fettling I've done. Hats off to J7 for doing these day in day out.

Jim's post referred to above was extremely helpful and gave me the courage (recklessness ) to do it. I think Covid lockdown boredom also played a big part

I came across a few things that together with Jim's post others hopefully may find helpful if contemplating doing this but be warned it is not for the faint hearted and if you loose a wire it could be FUBAR time
Don't attempt this after a few wines/beers/joint () the night before and avoid that morning coffee. You do need a steady hand.
This is a long post so apologies for that and also for sounding like your mother

So in order:

1: You need the right tools and all to hand. Low power soldering iron (I used a 12 watt one). Digital volt meter for checking continuity (more of this later). Some device/clamp/helping hand to hold bits to be soldered. Forceps (tweezers) curved and straight. A dental probe/pick for teasing out the wires and more. I rank this item as mandatory. Scalpel or modelling knife. Cross head screw drivers (3 sizes). Several lengths of single strand bare copper wire to act as pull throughs - life savers if you loose a wire inside the base or arm tube (more of this later as well). A smarthphone/camera to document all the stages and aid refitting. A bright light to illuminate your work surface. I also found a magnifying glass helpful but then I'm old and blind And of course your chosen tone arm wire.
KAB supply a ready made pack with all you need with the new wire cut to the correct length (10.25 inches) but because I am running direct to the KAB plate I needed significantly longer lengths so I used the Isokinetic litz rewire kit which has 5 metres of wire - more than enough and allows for screw ups and wastage https://www.ebay.co.uk/itm/ISOKINETI...72.m2749.l2649

2. Prepare your new tonearm wires. I cut mine to 18 inches. I found the easiest way to prepare the ends for soldering is to gently scrape off a few mm of coating with a sharp scalpel on a glass plate. Don't cut. Just a few firm scrapes then tin the ends. Before you forget colour code the ends of each wire - I used acrylic paints R, W, G, B - just a thin smear for a few inches and set aside to dry.

3. I was fortunate that my tonearm was off the deck already. I've seen posts where folk have rewired with the arm in situ but this is tricky enough as it is and you really need to be able to turn the arm through all sorts of planes to get a good view so best remove the arm. Obviously, remove the counterweight and also zip tie the arm tube to the support.
Tip: put an old headshell with leads in the bayonet. This stops the pins springing out when you desolder the old wires and also facilitates continuity checking all the way from headshell lead to the end s of your new wires.
Remove base plate and desolder the existing tone arm wires. I advise leaving the black tone arm ground wire in situ. It's easily lost inside the base and would be a nightmare to retrieve and there is no advantage in removing it. Just gentle low heat and flick the wires off with the dental pick - don't pull. If there is a tonearm wire desolder that as well after cutting the plastic zip tie.

4. Trim and tin the desoldered ends of the existing wires and solder a new wire to each of them.
Tip: It is vital that the joint is as thin as possible otherwise they will not pass up through the base. Solder the wires end to end not overlapping. This is critical. If the joint is too thick at best it wont go past the entry hole at worst it will get stuck somewhere and break and you will loose your old wire. The tonearm wires take a circuitous route through the arm base and up to the arm tube - they do 2 dog legs so there is no way you can feed a wire this thin and pliable through - it will go down the wrong hole/channel. Do all 4. The handy clamp/clip is helpful but not mandatory if you have a steady hand.
Tip. If you use a clip/clamp wrap the old lead in a bit of wadding so you don't crush it (I used a cut up bit of alco wipe).

5. Remove the bayonet connector on the business end of the tonearm. Make sure there is a headshell inserted. Remove the 2 very small screws on the underside of the arm - put them in a jar or tin for safe keeping. Several posters including KAB say removing the bayonet can be difficult and it needs easing out while twisting. I was lucky mine was very free. It did occur to me that maybe someone had been here before and already rewired the arm
Gently pull the fitting out the end of the arm tube but not very far at this stage. I suggest not desoldering the tags yet. I've seen posts that do remove all the wires from the bayonet fixing at this stage but if you do it's all too easy to pull one of them into the arm tube while you are concentrating on another task and then it's lost and your up sh1t creek. Well not completely but the fix is trixy.

6. Now the real fun begins One at a time very gently and slowly pull on one of the old leads at the bayonet connector and feed it with it's soldered mate up the channel in the arm tube base.
Tip: Any resistance is too much! If the wire feels tight or snags DO NOT PULL harder. Gently pull the wire back out and check the solder joint. I guarantee if it is the correct width the wires will slip up the channel with a minimum of force and a little "ziz" sound as they pass up through the channel. Don't be tempted to pull more than one wire at a time. With luck you will see the new wire start to emerge from the top of the arm base. Pull it a few inches and stop. Repeat this for the other 3 wires. Don't be tempted to do a wire all the way to the headshell at this stage - if you break a wire (as I did twice) you will need a "good wire" to get you out of trouble (more on this later). Note the joints in picture 5 are too thick and needed to be thinned.

7. When all 4 new wires have emerged safely from the top of the arm base you are now ready to feed them into the arm tube. Check all the joints for security. Probably a good idea to take a rest for a few minutes (hours/days )

8. Again 1 at a time feed each wire into the hole on the underside of the tonearm by gently pulling on a lead at the bayonet fixing. Make sure the wire does not get snagged or wrapped around the black ground wire keep it separate with the dental pick/probe.If they went up the arm base OK then they will slip along the arm tube with ease. Just be aware that there is a lip on the edge of the arm tube opening so gently feed the wire through with a pair of forceps while pulling on the end. Pull the wire all the way through and out the end of the arm tube but not too far. If you are going to solder the other ends to the PCB in the base and you have cut your wires to the standard 10.25" then you need to prevent the wire being pulled up into the arm base channel or you will loose it and your sunk again. I didn't have this issue as my wires were longer but I'd suggest putting a bit of masking tape on the ends at this stage. Repeat for all 4 and breath a sigh of relief. Nearly done but plenty still time for a FUBAR moment
This is a good time to check continuity with the DVM.

9. Time to desolder the bayonet tags. Do these 1 at a time. Make sure the headshell is attached. Pry off the plastic insulation (very tight) and put aside. Desolder the old wire. The KAB instructions are very clear to put a heatsink (locking forcep/clip) on the tag when you do this. I did but my soldering iron then wouldn't melt the old solder so I took it off. I'm guessing 12 watts is OK without a heat sink. Apply new solder to the tag. Slip the old (or new) insulation over the end of the new wire and solder it to the tag. Slide the insulating sleeve over the tag.
Tip. Don't slide the insulation all the way to the back of the bayonet fixing. It may look neat but it will impede the spring action of the pins inside the bayonet. I found out the hard way Having checked and got good continuity at all stages I went ahead and put the bayonet back only to find only to find I'd only got continuity on 1 channel . Looking into the end of the arm it was clear that 3 of the 4 pins were stuck down. I had to remove the bayonet and trim back the insulation on 3 pins and then all was well but a bit of a tense moment coming near the end of the job. Repeat for all 4 and check continuity. At this stage I put some cotton fibre wadding down the arm tube (actually filling from a cheap duvet ). KAB used to supply cotton strips for this but now use a thin vinyl tube which Kevin reckons is much better but you have to put this in from the rear of the arm tube which means removing the arm tube from the bearing which I absolutely didn't want to do. TBH I have no idea if the wadding will make any difference to damping the tube but as I was there ......

10. Replace the bayonet fixing in the end of the arm tube - don't crush/crimp the wires as it goes in and secure with the 2 tiny screws you put aside earlier. Check continuity from the headshell leads to the ends of each new wire in the base and fingers crossed.

11. Gently pull the wires from the base to "snug up" the 4 wires where they pass from the rear of the armtube into the top of the bas. A good light and magnifying glass are helpful here. Use the dental pick/probe to ensure each wire runs separately and is not snagged. Spend some time getting this right. Each wire should lay flat side by side.

12. Time to solder the ends to the PCB if that is your aim. I fed mine through a piece of sleeving and zip tied that to the PCB to secure it as they will eventually be soldered to the KAB jack plate at the rear of the deck.

13. Replace the base plate and cable clamp. Check for continuity - again

And that's it - job done. Took me all day. Not sure I'd do it again and it will be several weeks before I can install the arm to see if it actually works.

Tip: So what happens if you loose a wire in the arm tube (bad) or base channel (badder)? This happened to me twice - 1 in each location. The first time I lost the 3rd wire in the base and the second time I pulled the old white wire into the depths of the arm tube. I must admit to feeling sick at the consequences It crossed my mind I'd buggered up a perfectly good arm and would have to send it to J7 and feel a real idiot. It took a bit of thinking through but this is what worked for me and maybe it will help you out of a tight spot.

You will need a length of single strand bare copper wire. I pulled one out of a standard multi-strand wire the gauge you would use in an amp circuit board. Length depends on whether you lost the wire in the base short) or arm tube (long).
As an example - say you have broken a wire joint in the arm base . Pull the old wire you lost the connection to up through the top of the arm base and don't loose the end. Pull the new broken/lost wire back out of the arm base Solder it and the tip of the copper strand to the end of a wire you have already pulled through. Identify this wire where it emerges through the top of the arm base by pulling on the various wires with the dental pick/probe. Very gently pull this wire up through the arm base bringing with it your new wire and the copper strand. Make sure the copper strand is long enough that a goodly bit remains at the arm base. It's a good idea to put a clip on it. When the tip of the new wire/copper strand appear at the top of the arm base cut off (don't desolder) the new wire but leave the copper strand attached to the pull through wire. Now gently pull the end of the copper strand to pull your good wire back into the base. Solder the new wire to the cut end at the wire between arm tube and arm base and gently pull it into the arm tube as described above. Judicious use of the dental pick/probe is recommended to coax the wires along. This probably all sounds very confusing but if it happens to you it will all make sense (hopefully).

Enjoy - or decide not to do it in the first place

[worrasf]

And the rest of the photos