Hi all,
as I received a lot of support and good advise on my projects, I want to share the experience I had with a SME-Headshell mount.
My cousin, who lives a few hours drive away, had his Thorens TD 125 with SME 3009 II arm to a HiFi workshop because he lost one channel. After a few days the shop called and said that the tonearm was beyond repair.
Now during the christmas break we met and the deck came to me.
After a few simple checks it was clear that there is a problem with the SME-mount- the inner pins weren't "springy".
Two of them were pressed-in deeply and didn't move at all. The other two moved fine.
(For those who aren't that expierienced with SME-mount / Headshells: the pins on the headshell are fixed, the ones in the tonearm are springloaded, to compensate tolerances between different headshells).
As the SME-mounts are hard to find and quite expensive, I decided I'll give it a try to fix it.
It's a "all or nothing" anyway...
First step is to remove the Tonearm from the deck and completely dismantle it until only the tonarm tube with the SME-mount and the wires are left. Remove the litte screw from underneath (already gone in the picture).
then carefully pull the SME-mount out of the tube. Make sure the wires at the other end of the tube are free to follow the mount.
To un-solder the wires, INSTALL A HEADSHELL AS HEATSINK !!! Additionally, I used a haemostat, these scissor-like, lockable pliers, used in surgery...
At this point I could see that two of the pins showed sings of overheating. Note the heatmarks round the bottom two pins!
The pins were stuck. Several attempts to free them with WD40 or graphite failed.
So I decided to remove the plastic part, holding the pins, from the alloy body. I slightly bent up the "alloy toungs". Then I wrappen a cloth, soaked in boiling water, arround the alloy body to heat it up, hoping it woud expand slightly. After a few seconds, I pushed the plastic body out of the alloy body from the front, using a 5mm allen key(maybe a slotted screwdriver would have been better...). This worked surprisingly well.
It took me some moments to realise that the plastic body was actually broken into two parts. The front piece...
The back, carrying the pin/ spring assemblies...
how it should be, more or less...
I didn't realize it breaking, not sure if this was alrady defective before I started my attempts.
At least this gave me a good insight and I realized that the two pins not moving were really blocked in the back part, with the molten plastic arround.
I now applied some grinding compound (typically used to remove spray paint) and moved the pins 10-20 times in and out. This freed them up notably. I cleaned the parts now in an ultra sonic bath, but I'm sure a good rinse of water or break cleaner will do as well.
When dry, I glued the the two parts with "Superglue" (cyanacrylat), very carefully applied with a wettened toothpick. Do not use big drops out of the tube! This would be a perfect point to f*** this job up!
Make sure no excess glue is on the outside of the plastic. If so, remove carefully.
Again, I heated up the alloy body with a cloth soaked in boiling water.
This time I pressed in the plastic body with a sloted screwdriver, to avoid any force to the pins.
Make sure its carefully adjusted before pressing in. Any attempt to turn the plastic body inside the alloy might damage the assembly.
If you are happy with the result and the pins are moving freely, make sure to put the old insulation tubes on the wires and resolder the wires, applying the same heat-sink mesures as before.
Make sure to use a high quality soldering iron, that will heat the contact pint in less than a second.
Apply a little amount fluxing compound to the contact pin at the SME-mount, have a little amount of tin on the tip of the soldering iron. Then heat the pin and connect the wire at once. DO NOT MELT THE PLASTIC OF THE PIN ASSY!
Finally push the insulation tubes over soldering points.
Check is all four contact pins are moving "springy".
Now push the SME-mount back into the tonearm tube. At the other end, carefully pull the wires back (keep the black wire separate- it's not connected to the SME-mount).
Now re-assemble the tonearm, install it to the deck and try as many SME-Headshells as you like.
Happy new year to all of you and good luck.
Stefan
