Technics SL-1300 MK2 78 rpm mod I've made an interesting discovery regarding modifying a Technics SL-1300 MK2 to add a 78 rpm mode. (I am referring to the MK2 not the original model, the original model mod is well known and involves an added resistor.) It may be some time before I get a chance to dig into one of my units, but here is the information I have found. The SL-1300 MK2 uses the DN860 chip to generate the reference frequencies needed for 33 and 45 rpm speeds. Note that this appears to be the same chip that is used in the SP-10 MK3 with the variable speed control that does 33, 45 and 78 rpm. From the service manual for the SP-10 MK3, it looks like pin 12 can be used to select the chip mode that generates the frequency needed for 78 rpm. The mod might be as simple as adding a switch from the chip side of R205 to ground (similar in function to S201 and S202). However, there are two nuances to consider. 1) One is that on the SL-1300 MK2 the 33/45 selection modifies the auto-return time constant. Not sure the impact of 78 rpm on the auto-return function. (Although I assume no impact if manual return is used.) 2) The other is that the SP-10 series uses different divider resistors for 33, 45 and 78 rpm selections on the AN-660 control circuit (IC203 on the SP-10 and IC202 on the SP-1300 MK2.) The SP-1300 MK2 uses a single resistor configuration for both 33 and 45 rpm. This divider may or may not be sufficient for stability or locking at 78 rpm also. Obviously, it may not be optimum at each frequency, but might be adequate. If so, no modifications may be needed to this part of the circuit. If anyone knows anything about points 1 or 2, I would appreciate some feedback. Although depending on the answers to 1 and 2, the mod may be as simple as adding a switch, a cleaner implication would involve the adding of a simple circuit to allow selection of the 78 mode by pressing both 33 and 45 buttons simultaneously. Also, with a little additional work, the display could display the correct number 78 when that mode is selected. I've worked out the details, but it may be a while before I can do it. The circuit details can be posted once I see if the mod works as desired.