[sdiy] Solved: Crumar Performer - keyboard mystery

Florian Anwander fanwander at mnet-online.de
Fri Aug 10 14:34:44 CEST 2018

Hi Andre

Am 10.08.2018 um 13:18 schrieb Andre Majorel:
>> The problem was caused by a too high voltage on the keyboard
>> bus, which again was caused from the "Crescendo"-circuit,
> Never would have guessed. Thanks for telling us the end of the
> story.
The interesting part is, that appearently the transistor array inside 
the TDA1008 lets bleed thru the signal of the dividers if it is getting 
a too high control signal. It started when the ontrol voltage became 
close to the supply voltage. And appearently the variation of the 
resistors which provide the controlling signal caused that some keys had 
this bleed thru and others did not - even in the same IC.



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