[sdiy] Glowing diode on Casio CT-510 analog board?

Roman Sowa modular at go2.pl
Tue May 23 09:52:48 CEST 2023


If it glows, it is LED.
Those kind of early LEDs were used at least in one of the Korgs, Maybe 
Poly6 or Poly61, can't recall now, to indicate active voice.
I was shocked too when I saw them first.

Maybe it's there just to make some cool light, but knowing early 
japanese designer's practice of cutting corners, this was probably used 
as voltage reference.

FWIW, back in the 90's I used 4 LEDs to create expo converter to drive 
VCF. Turned out to be accurate enough for the filter. And it looks so 
cool when played, especially with deep LFO. Too bad I have to open the 
case to see it.

Roman

W dniu 2023-05-23 o 02:53, Benjamin Tremblay via Synth-diy pisze:
> Here it is.
> 
> 
> 
> 
> Benjamin Tremblay
> 
>> On May 22, 2023, at 8:41 PM, Benjamin Tremblay <btremblay at me.com> wrote:
>>
>> Sorry if this is way way way off topic. I’m trying to fix this Casiotone keyboard and there are no schematics. The power supply seems to be putting out around 4 volts. The logic board runs but the 4558, 4066, and power amplifiers seem inert.
>> I’m trying to trace the power supply. Unlike most Casios from the 80s, the 5 volt regulator is just a zener diode, not a 7805. There’s one more non-zener diode on the board, and it’s faintly glowing red (!)
>> I know all diodes emit radiation when they are operating, but this one has such and led-red color.
>> Were such diodes ever used to indicate an overload on the board? I was more interested in fluorescent hair gel than power supplies  when this keyboard was made.
>> <image2.jpeg>
>>
>> (Lower left corner, a normal looking glass diode)
>> Benjamin Tremblay
>>
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