Hi David,
Thanks for the info and happy new year to you as well! This is actually the second time you've helped me, as I've been going by the CS-80 schematics and block diagrams from your website - thanks for uploading those!
I do have an oscilloscope, so will give it a whirl, and will try removing IC4 and see if pin 3 is still +15v. I'm also wondering what effect the TKC board has on the A, B, and C inputs of the 4051, and if that could be the culprit. One guy on Muffwiggler suggested a possible broken trace or wire going to the aftertouch PCB under the keyboard, and that if the -15v rail wasn't getting to this board, +15v at pin 3 could be the symptom. Another said to simply wiggle all the spider webs of wires going to the solder pads, as they can detach over time. So I have a few things to try. That thread can be found here: https://www.muffwiggler.com/forum/viewtopic.php?t=193847
For some reason, the last tech that serviced this board installed JRC 072BD's in place of the old 4558's. Am not sure if this is a common swap, but the design on their respective data sheets looked pretty close. Pin-outs are the same, just some subtle differences in the actual circuit.
Cheers,
Jonathan
Thanks for the info and happy new year to you as well! This is actually the second time you've helped me, as I've been going by the CS-80 schematics and block diagrams from your website - thanks for uploading those!
I do have an oscilloscope, so will give it a whirl, and will try removing IC4 and see if pin 3 is still +15v. I'm also wondering what effect the TKC board has on the A, B, and C inputs of the 4051, and if that could be the culprit. One guy on Muffwiggler suggested a possible broken trace or wire going to the aftertouch PCB under the keyboard, and that if the -15v rail wasn't getting to this board, +15v at pin 3 could be the symptom. Another said to simply wiggle all the spider webs of wires going to the solder pads, as they can detach over time. So I have a few things to try. That thread can be found here: https://www.muffwiggler.com/forum/viewtopic.php?t=193847
For some reason, the last tech that serviced this board installed JRC 072BD's in place of the old 4558's. Am not sure if this is a common swap, but the design on their respective data sheets looked pretty close. Pin-outs are the same, just some subtle differences in the actual circuit.
Cheers,
Jonathan