I got the 4069 ICs in the buffered version. I replaced the one that could have been faulty (with a socket) and the problem remained. I have already replaced IC1 and IC2 (4558) a while ago. I also replaced IC3 (4558) an hour ago. Didn't change anything. I also crimped new contacts to the connector that goes to the main board for the percussion thing. Didn't change anything.
BUT!
Yesterday when I started to desolder the old 4069 inverter, all of a sudden a metal washer fell from the pcb. It must have been there for quite a while - somewhere hidden between some parts - and I haven't discovered it until it fell down! I suppose it fell on that pcb the same day when the percussion function refused to work correctly.
Unfortunately I cannot really tell you where it was stuck. I have seen in which area it must have been hiding, because of the direction of the fall. I suppose it was in the area of VR7 (http://robert.weathergreen.com/bx3/klm245_pcb.gif). There are lots of components. My stab in the dark is that it could have blown a transistor. What do you think? And which one could it be?
Here's the percussion schematic again:
So far I think that all the electrolytic capacitors have been replaced correctly. All the electrolytics are brand new. The 4558's and the 4069 work like a charm (so I think). There is no real possibility that IC1 or IC2 may have been influenced by the metal washer. I would have seen the washer while replacing these ICs. I just wonder that it could hide for such a long time. I have worked at that board several times in the meantime.
What else apart from transistors may have refused to work?
