[sdiy] Digital encoders missing codes in many devices - why?

Roman Sowa modular at go2.pl
Sat Aug 21 20:22:44 CEST 2021


To self-clean contact you need at least 11V on them. That is enough to 
make a tiny invisible spark when they are getting really close and burn 
the oxidation, or better yet - siler sulfide, making the contact good as 
new. That's the reason why old organs have worked for 30 years if played 
regularly but when someone installed MIDI encoders on the same contacts 
(and they work at 5V) then after some time contacts went bad even if the 
organ was played daily.
That's my job to know that and I've learn it the hard way. And why it's 
11 and not 12 or 10.5 - I've read that in some wise document I can't 
remember where, but the number 11 is carved in my head with a nail.
It's the voltage (think spark) that works here more than current, but 
anyway some people have gone one step further and changed pullups in 
their organs' contacts to 200 ohms. From 15V rail. That's a lot of heat. 
Well, higher current may also burn something out, opening path to better 
conducting layer below.

I've also "restored" old unreliable switches in Elka Synthex this way, 
connecting them to 30V via resistor and pushing few dozen times. The 
on-resistance went down to sub-ohm and didn't change regardless how and 
where you pushed it. In contrary to their condition before that.

Roman

W dniu 2021-08-21 o 19:47, MTG pisze:
> What was the Dave Smith encoder debacle all about (and solution)? This 
> was quite a while ago, I don't even remember what synth it was.
>
> Someone in this thread also mentioned current and pull-up resistors. I 
> think Moog had an issue around the time of the MemoryMoog or maybe the 
> Source where the panel switches were oxidizing and getting 
> intermittent. The ECO was to reduce the pullup resistor value 
> substantially.
>
> GB
>
> On 8/21/2021 9:04 AM, David Riley via Synth-diy wrote:
>> On Aug 21, 2021, at 09:24, cheater cheater via Synth-diy 
>> <synth-diy at synth-diy.org> wrote:
>>>
>>>
>>> Why does this happen? Why is it so spread out? Is this a programming
>>> issue, or a mechanical issue related to the lifetime of the encoder?
>>
>> Having made these before at various different scales, I’d guess that 
>> it’s probably mechanical quadrature encoders using brushes to 
>> contact. If so, intermittent brush contact would do exactly that; a 
>> lot of decoders also don’t handle things like simultaneous 
>> transitions well.
>>
>> There’s a reason ball mice used optical encoders. They last 
>> practically forever. Most brushless DC motors and other servos also 
>> use optical encoders. For some military hardware I worked with (the 
>> carrier-side instrument landing system antenna motors), we used a 
>> magnetic encoder, which I’ve not seen elsewhere.
>>
>> Anyway, degrading contacts would be my guess. Either bent or dirty 
>> brushes. Does a hit of De-Ox-It help?
>>
>>
>> - Dave
>>
>>
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