[sdiy] Andromeda A6 repair?

Barry Klein Barry.L.Klein at wdc.com
Wed Jan 14 20:14:47 CET 2015


>Recently I heard that in today's fast digital circuits 0.01 uF are better suited for supply decoupling than 0.1 uF caps. The resonant frequency of smaller caps is higher.

Yeah I read some papers from companies like HP that even suggested 3 values in parallel.
The thing about this synth design is that there really is not much bulk capacitance.
The supplies are linear regulators like the LM317.  
Here in our products I think we use a lot of .1uF's.  Also larger like 1uF, 2.2uf, and 10uF for chips with higher current VDD requirements.
A board as big as this A6 main board seems kinda light with just local .01uf's and the caps in the regulator circuit 8 inches away.
The way this synth has such an irregular boot behavior it is something analog causing it.  I'm thinking the caps could help.
There seems to be a good reset hold off on initial power (dedicated reset chip).
Could be irregular xtal behavior too I suppose.

Barry





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