My first stereo system component was a Harman Kardon Rabco ST-7. This is a very sweet linear tracking turntable and for several months it just sat on a shelf as I admired my 1st purchase. At that point I had nothing to hook it up to!
Well after a couple of decades in retirement, it’s back in service. The main driver for this revival was a gift of Hillsongs Zion on vinyl from Scott and Mandy on my birthday. It hooked effortlessly into my current audio system, and even had a space waiting for it on the shelf.
However, halfway through the first song, things came to a screeching halt, quite literally. The tone arm mechanism was not tracking properly and trailed the arm is such a way that it pinned it down to the record. Not good.
Well, after 20+ years of just sitting around, I guess a little maintenance work is to be expected. The ST-7 is notoriously finicky to get set up correctly, but once you’ve got it, its a thing of beauty. After removing the back cover plate it became clear that there was a lot of buildup and “gunk” on the tracking shaft which is instrumental in keeping the arm moving properly across the record. After cleaning that I my attention turned to the small tracking roller that rides on the tracking shaft roller tube. It had similar looking gunk on it. Armed with a Q-tip and alcohol (for cleaning purposes on the Q-tip) I started to clean the roller. A short time into that process and I started to wonder if this was normal, and what is this gunky stuff.
Google to the rescue. It turns out this “gunk” is what’s left of the silicone ring that is fitted onto the roller. For the ST-7 this is a well known maintenance issue, and from all the descriptions I could locate on the web, very challenging to get the roller out. Once out you can replace the silicone ring with a fairly standard plumbing o-ring from Home Depot. The challenge is getting the roller out and back in without breaking anything or doing a full and complex disassembly. The roller is in a plastic U shaped holder, with very limited access. Apparently surgical tools and surgical skills are a asset in doing this repair.
Perhaps some more disassembly will assist in getting this thing out. Next thing you know my ST-7 looks like this, stripped of all it’s aluminium finery.
The roller that I need to replace is in here, behind that metal plate with the screw sticking out (Tracking adjuster), cradled in that light grey plastic piece that you can hardly see.
After quite some time and some careful exploration, the roller is out!
Apparently, the roller is not symmetrical, some 0.20 mm wider on one end than the other so I get a measure to ensure it goes back in the right way. That brown stuff is like a gummy bear that has melted down and wrapped itself around the roller. Cleaning it up and putting the new o-ring on is easy. Another hour to get the roller back into it’s holder.
After a few re-assembly goofs, it’s all back together and running. I probably spent another 1-2 hours adjusting the tracking while enjoying some resurrected albums from the storage areas that we’re saved from my collecting days.
I’m sure there will be a little more vinyl in my listening future.