rbphoto
Member
Hi all,
I'm reviving this old thread because I have an SL-1600mk2 with exactly the same symptoms as OP, and I managed to fix it today so sharing here to help others who may encounter this fault.
The basic issue is that the tonearm control IC (IC401 on the main PCB) is getting random spurious inputs from the tonearm position sensors and in turn it triggers the platter motor and auto return erroneously.
The tonearm position sensors are the three photo interruptor switches PC501 (rest), PC502 (end), PC503 (start) that are actuated by the adjustable arms that move with the tonearm itself.
In my case I could see that all three LEDs on the switches were lit, but when probing the inputs of IC401 it was obvious that the phototransistor part of two switches PC502 and 503 were bad - the voltages were all over the place and not consistent with the arm moving.
The original Panasonic part ON1128 is long ago discontinued, but I was able to substitute a Kingbright KTIR0611S successfully. These have slightly different dimensions but crucially the lead spacing worked and operating specs were close enough.
Note though that the Kingbright part has the LED in reverse polarity, so I had to switch the LED wires on the two small PCBs in those cases.
The black plastic housing is a little taller, I trimmed down the two locating stubs and took a notch out of the securing latch in the white plastic locating part to make it seat properly, I also added some silicon to keep it in place and checked the spring loaded screw adjustment was keeping it horizontal.
I didn't need to transfer the metal apertures from the Panasonic switches, the new ones just worked but in theory are a little less precise.
In practice the tonearm set down and pickup points are repeatable to within a millimetre or so, good enough.
The Kingbright part can be found at Newark/Farnell/Element14, order code 2079964.
Hope that helps!
I'm reviving this old thread because I have an SL-1600mk2 with exactly the same symptoms as OP, and I managed to fix it today so sharing here to help others who may encounter this fault.
The basic issue is that the tonearm control IC (IC401 on the main PCB) is getting random spurious inputs from the tonearm position sensors and in turn it triggers the platter motor and auto return erroneously.
The tonearm position sensors are the three photo interruptor switches PC501 (rest), PC502 (end), PC503 (start) that are actuated by the adjustable arms that move with the tonearm itself.
In my case I could see that all three LEDs on the switches were lit, but when probing the inputs of IC401 it was obvious that the phototransistor part of two switches PC502 and 503 were bad - the voltages were all over the place and not consistent with the arm moving.
The original Panasonic part ON1128 is long ago discontinued, but I was able to substitute a Kingbright KTIR0611S successfully. These have slightly different dimensions but crucially the lead spacing worked and operating specs were close enough.
Note though that the Kingbright part has the LED in reverse polarity, so I had to switch the LED wires on the two small PCBs in those cases.
The black plastic housing is a little taller, I trimmed down the two locating stubs and took a notch out of the securing latch in the white plastic locating part to make it seat properly, I also added some silicon to keep it in place and checked the spring loaded screw adjustment was keeping it horizontal.
I didn't need to transfer the metal apertures from the Panasonic switches, the new ones just worked but in theory are a little less precise.
In practice the tonearm set down and pickup points are repeatable to within a millimetre or so, good enough.
The Kingbright part can be found at Newark/Farnell/Element14, order code 2079964.
Hope that helps!
