One day, a friend of mine wanted to create a song with his Acetone Rhythm Ace FR-1. We found out, that the unit just played barely hearable 16step clicks instead of the pattern. I took the unit with me for repair. Since there was not much information available I reversed engineered parts of the drum machine and found out, the fault must be within the trigger section. The FR-1 has a clock signal, divided by flip-flops which breaks down the clock into reasonable rhythm timing. So what can go bad with these parts? I first suspected the electrolytic capacitors since they are old, can dry out and the quality back in the day wasn’t as good as today for all parts. And indeed, they were leaky by ESR (value or Q) and so I changed them, what in my mind is mostly a good idea. But this didn´t fix the problem. So next I suspected the germanium transistors. In the trigger section they are used as switches, so I temporarily swapped them with silicon ones. But that also didn´t fix the problem, which makes sense. The poly caps usually don´t go bad, so the only part(s) left were the carbon composite (Alan Bradley Style) resistors, which often go out of tolerance. So I measured them in circuit to see if they were way off. And yes, that was the fault. I find one, which fell apart while desoldering and also found a lot more which were way out of spec.
Usually my restoration process is to replace the components with the same like before, so I ordered new carbon composite resistors and what can I say, the unit worked perfect. Like always, here are more inside repair pics for you.