Cartridge Surgery!

Cartridge Surgery!

In the VE forums at the moment there are details of some successful repair work done on a Shure M97xE (resoldering of unsoldered pins). That made me smile as I've had to do somewhat similar things to one of my M97xE's in order to restore it to life and full working condition. It is the M97xE that lives on my Pye TA5A's tonearm in my 'spare room' system. It is the M97xE that I have that gets the most use and in a way I feel the need to give it plenty of use, given how close it came to being turfed into the bin. Sadly that has happened to a few phono cartridges I've had, mostly as a result of my own sheer stupidity, after doing things like soldering headshell wires direct to the cartridge pins. Please DON'T do this, as open circuit coil wires mean (in most cases) a completely ruined cartridge! I did this to a beautiful Grace F9 phono cartridge that I once owned and although it was many years ago, I've never really forgiven myself for being such a @#%$^&# idiot! More recently I managed to pull out one of the pins on a perfectly good Ortofon Super OM cartridge thanks to some 'hamfistedness' on my part. That was a very painful and expensive experience too!

Back to the M97xE story! Well the problem started when the mounting bar 'glued' to the cartridge body broke away without warning. Although apparently many phono cartridge manufacturers make routine use of 'gluing' parts together, I've always thought this approach was/ is a little lacking, although in thinking about it there are probably no other options. I have actually heard of this happening to others as well so I wasn't the only one this has happened to, it would seem!

Re 're-gluing', it seemed quite straightforward to do this but I made one serious mistake. In order to improve the strength of the glue bond I firstly scrapped away all of the black 'paint' from the cartridge body, which was a big mistake in hindsight! After the 'job' was done and everything reinstalled I found that I had a loud permanent hum in one channel and initially I couldn't work out the reason. Eventually I realised that the black 'paint' was more than just there for decoration! It was also there as an (electrical) insulating layer and its removal allowed an earth loop and hum to develop! I've since become aware that the internal 'earthing' arrangements of Shure phono cartridges are a little unusual.

So I had a problem, either accept the hum, or re-establish another kind of insulating layer between the cartridge body and the attached mounting bar. Firstly I had to 'unglue' my repair which I was reluctant to do as I had used a high strength cyanocryalate adhesive. However I was able to break the join apart without incident and then I had to find a way to re-insulate the layer. My first attempts using paint were completely unsuccessful. The disassembled cartridge sent on a shelf for some months until one day when I decided to have another go. I had purchased a can of marine grade varnish for another application and it thus occurred to me that perhaps it would be suitable for the job, and so it turned out to be!

It was a delicate job, but I was determined to make a success of the task. After cleaning the cartridge body and mounting bar of all evidence of previous repair attempts, I applied several layers of varnish, a task that took the better part of a day to allow the varnish to dry thoroughly in the sun. I then held my breath and prayed as I re-glued the mounting bar to the cartridge body. I was almost prepared for another failure, but after everything was completely dry I trotted out my digital multimeter set to high ohms continuity range and no unwanted 'shorts' were detected. I cleaned up the cartridge and reinstalled it in its headshell and a test, playing records followed and...........no hum, just nice music. As a present to the cartridge, I obtained a nice new stylus. The surgery was completely successful! That cartridge is still working happily to this day. It is nice to have a 'win' occasionally! More to come. Felix.