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Well, that kind of smart. So I think I got a bad chip (HD) I will try swap them to see if it change things, I come back.

Well I have checked D/A out and after both opamp I can get a signal , by the way this one has only one AM6012 at the second 43517 and at the first 43517 there is a resistor adder so what puzzle me how can it skip some key presses but still play the right notes , there must be something counting . So the 701 plays all tones but only at a sudden patten every 5th or 7th or I can trig 4 notes at a time , the max notes I can get is four

re-Cable is fine I have full respond via keyb. bus system , also I can see the LED flashing at key press and the the problem are on all keys. The fault is it plays notes every 5 or 7th time, it I can get four notes playing after pressing the keys in sequence. I have have check both "analog out" and they have signal out so it is not after HD43517. it is like it is "counting" and only plays some of notes at this patten 5 or 7/8, in "fingered" mode it jumps tone in octaves !

So the CPU "calls" and tell the HD43517 chip which has the "sounds" has to be, and each 43517 has 4 notes ! It is not the CPU who does the sounds. Like with normal CPU /DAC setup where it is all software !? The damm thing is that it worked before I change the keybed ribbon cabel 😥 That make me think that something eles is wrong than the chip(s)

I do not know, but I do repair of alot vintage gear and yes chips can fail. But first I had to change the cable from the keybed the metal on the flex cable was crack /missing given the tone failing out and I did a re-cap on the main board and THEN after that I got this "New" problem !!! And it puzzle me if i have do something wrong but all looks good and after the help from @CYBERYOGI schematic I narrow it down to be the LSI chips ,somehow

Nice thread, I have a 701 with similar problem, it plays only note every 5th or 8th time I hit the keys and drop an octav on the third time !!? So I guess one of the chips are broken too Everything else works fine , and I can not believe the fault should be the CPU , the keyboard input is fine to !! Any one have a HD43517 IC they would like to sell ?