Harmon Kardon ST-7 Resurrection

[DavidE]

Hello all. I joined this group, mainly for my own selfish benefit. I'm resurrecting my old audio equipment and need some professional help in the process.

Initially, I'm trying to get my Harmon Kardon ST-7 TT up and running. Still have the manuals and original receipt from 1977. I remember it having a tracking issue when I put it away. I've read what threads I could find on AK and have gotten ideas as to where to start. I've broken the unit down to its skeleton, finding the drive belt in good condition (will replace it anyway), but the drive wheel not so. Saw where a #31 o-ring from Lowes may work as a replacement wheel and I still need to purchase that.

The drive motor is a bit noisy ... has quieted some with exercise, but am wondering if it can be lubricated with spray via the shaft opening. I definitely don't want to gunk anything up with WD-40 if that's what it'll do. Also, I am not versed in cartridges and needles. It currently has a JVC cartridge with a 4-channel stylus (not sure why), which I'm sure needs to be replaced. Can the cartridge be reused, or must the entire unit be replaced? With what? Any recommended vendors?

DavidE

 

[cdk99]

Welcome!

I'd be hunting for a service manual. Check at vinylengine.com to see if they have one free.

Typically a stylus costs almost as much as a cart, so it's your chance to upgrade if you like. Or perhaps there's a gem of a replacement out there for cheap in a Pfansteil box.

If you search here for rabco st harman or your model number you should get a few previous threads to read through, including what carts people like.

 

[LesE]

David,

If your Papst motor is making a kind of scraping noise, you can try adjusting the thrust bearing at the bottom of the motor. Over time, the permanent magnet rotor assembly can slip down the motor shaft and begin rubbing against the PCB. By turning in the bearing, the motor shaft is raised providing clearance between the rotor and the PCB.

Les.

 

[heyraz]

Don't use WD-40. The vapors will attack anything rubber (like the mat) causing it to harden. It's even worse with the dust cover on as the vapors are trapped.

 

[DavidE]

I do have the original owners and tech manuals, but didn't find anything in them to address my concerns. I intuitively thought WD-40 would be a bad idea. The motor is not "scaping" but just sounds dry.
I'll do some more research on the cartridge/stylus issue. Will need to figure out "how important" this system will become. ($$$).
Upon second read, a Service Manual was suggested. This is different from the technical manual I already have, yeah?

 

[DavidE]

I've applied your suggestions, gone through the manuals I have, balanced the tone arm, and am still not able to get it to track correctly. The stylus leads the control arm and even with minute CW adjustments of the tracking adjuster, I'm unable to get it to center. I've even hit a point where a CW adjustment has INCREASED the lead of the stylus. Any suggestions? Am almost ready to box it up for another ten years.

 

[Montycat]

Did you ever replace the tracking roller? I think that should be your next step if not already done.

 

[DavidE]

I did "install" a #31 o-ring on the tracking roller as advised. THAT was a puzzle to be sure. Really surprised me that there was no rubber at all on the wheel; only goo. Not sure if it dissolved over time or what. Everything was reassembled and re-balanced afterwards per the manual(s). I cleaned the driveshaft with isopropol alcohol, in hopes of ensuring traction. The tracking wheel does rotate and I have not seen it skip or skid yet.