letate wrote:May I suggest taking a look at page 3 of the 60-L service manual. Pots VR1 and VR2 adjust speed for 33 and 45. If these are not adjusted properly, you can experience the condition you described. To adjust, the service manual suggests using an oscilloscope, but it can be done another way. If you are not experienced working with electrical circuits, I would suggest finding someone who is. This must be done with the turntable playing a record. So, remove the bottom, set the turntable so that you can get under it to adjust VR1 and VR2 while it is playing, minimal adjustment should be needed. Adjust until the speed is stable for both speeds - light on steady rather than flashing. Fairly easy, just need to be careful not to short anything, use a plastic rather than metal screwdriver. Radio tuning tools work well for this.
As the OP menationed: "The repair shop led me to remove the platter and clean the underside of the platter and the pickup sensor.
......a spot under the platter where the "black paint" has been stripped."
Obviously, that so-called "repair shop" doesn't know a darn thing about the sensitive nature of the magnetic coating, and suggesting a customer to mess with it is pure trouble, if not stupidity.
Since this coating is damaged, it will certainly throw off the pulses induced into the tape head sensing assembly, and also corrupt the data fed into the processor which controls speed.
There are hundreds of "pulses" recorded onto that coating, ALL are needed for rotational control, and if any are missing or damaged, then the processor cannot determine with accuracy one simple rotation of the platter.
Adjustments which you described may not Help in that case, which relies on NON damaged signal flow.