[CraigPSB]

Have a vintage T60 turntable from Harmon Kardon, original owner.  This unit has a quartz lock button for the speed, and you can also turn it off and manually adjust the speed. With the quarts lock enabled the speed is slow, maybe 32-1/2 instead of 33-1/3.  The service manual indicates this condition would call for a new motor pulley for the belt drive.  Seems like a weird fix.  Anyone familiar with this unit, and ever resolve this issue?  Obviously the motor pulleys are no longer available. 

A friend said try replacing the power supply caps as older caps can mess with the signal for the motor. 

[Sinnyone]

Easy to find out.  Open her up.  Either remove and check the capacitors or, since you got them out, just replace with new ones.  I have not seen a schematic on the TT, but shouldn't be much of a big deal.  First just look for discoloration and swelling.  Hell, just replace them all.

[WGH]

I modified my Harman Kardon T55C with good results, the Van Alstine mods for the T60 is exactly the same. The mod is easy and involves moving the vibrating transformer to an outboard power supply. I did all the Van Alstine Audio Basics mods and packed the base with modeling clay. The arm is low mass so a high compliance cartridge is best, the Grado with a Longhorn mod works very well with HK tables.

The turntable mods will cost you less than $50 and will make a big difference in regards to speed stability and imaging. Highly recommended.

I get much better imaging with the quartz lock off.

Here is a list of the Harman Kardon T60 articles from the Audio Basics newsletter with photos:
http://www.wghwoodworking.com/harman_kardon/h-k.htm

Download the Audio Basics newsletters here:
https://avahifi.com/pages/audio-basics-newsletters

[WGH]

A couple of free turntable tune-up apps will help you get the best out of your setup

Turntable Tune-Up Apps
https://www.audiocircle.com/index.php?topic=164173.msg1745439#msg1745439

The belts tend to stretch out over the years and slip which could be part of your problem. Replacements are available everywhere. The belts aren't magical, just get one that fits.

Based on the apps, my T55C measurements with quartz lock off are:
33.34 RPM + 0.01%
Wow: 33.29/33.38   +0.14%/-0.14%
       

[orthobiz]

I may be way off here but I've had success spraying Deoxit on the speed controller, then work the knob back and forth. The speed may become more stable. Good luck!

Paul