Ask at https://www.diyaudio.com/community/ , there are lot of experts there.
In fact I do wonder given the diagrams of the various chips in the service manual, do you think suitable replacements could be made on a breadboard?
I'm really asking for future use because these chips aren't getting made and we're going to hit a point to where the replacement cost of the chip will far exceeds the turntables value.
If you know that replacing the AN6680 will restore operation and you are dead set on getting the turntable operational then why not go on ebay and by one? I found a listing for one for less than $75 plus shipping. Technics AN6680 IC Linear Integrated Circuit Control Chip for sale online | eBay , you will spend more than this in trying to roll your own from scratch.
That's correct. Not for the electronic feedback, it's for the human working with it.
There are actually four series of dots on the edge of those turntables, and there's a red light shining on them. That light strobes with the mains power frequency (so 100 or 120 Hz) and the dots are for 33 rpm and 45 rpm. This way the dj has a visual indication of whether the turntable is running at the nominal speed (the line of dots for this line freq and rpm is not moving), faster or slower. That's important as the turntable has a slider to increase or decrease the speed, used for getting tracks to run in sync.
It should be quite straightforward using optical systems to detect those dots, reflective silver with black lines in between. That signal can then be used to adjust the speed of the turntable.
I agree that the control functions are within the range of an ATmega, but it will need some external analog glue. The interfaces have some odd analog ranges. The service manual appears to say the voltage on EC varies between 5V and 10V, depending on start/stop condition. The voltage on ECR appears to be a PWM pulse possibly varying between 1.2V and 5.2V, generated by VC and PO.
If I had a SL1200 to play with I could probably work it out, but of course the problem is they now cost more than I would be willing to pay. And I don't have any vinyl...
I see on the service manual there is a diagram showing what each pin does and what units are contained within the chip.
Do you think a non-integrated package could be made to replicate those function, or is it too complicated?
Something like one of the mixed signal ASICs from Dialog(Reneses) might be programmable to replace that chip.
Dialog
Where can I buy something like this? It appears to be a 24 pin DIP package too.
By the way I'm suspecting that a power surge might have killed the chip, how do I protect it from that in the future?
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