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 Forum index » DIY Hardware and Software » Circuit Bending
Casio SK1 power supply issues / understanding transistors
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wax+wire



Joined: Sep 28, 2014
Posts: 17
Location: Australia

PostPosted: Mon Jun 22, 2020 2:09 am    Post subject: Casio SK1 power supply issues / understanding transistors Reply with quote  Mark this post and the followings unread

Hey

So I'm having some trouble with the power supply circuit in my SK1 (actually, also my 5 & 8 too).

Casios still generate the 5Vs needed to power the CPU, RAM chips, percussion - everything. They don't however "turn on" the 7.5V (VA) needed to power the Amplifier IC that runs the speaker and headphone out. If I tap the audio before the IC, it is all good - interesting that the Casios have this complex circuit when 90% of it runs on 5V!

If you read from the service manual about the power supply I need to turn T8 on. So I need the right voltage (or is it current?) at the base of T8 to switch on the 7.5V. And it looks to me like I need to switch on T7 to turn on T8.

I think T7 is the issue.

Anyway I could test? Any ideas? I've got a working SK1 to compare with too!


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Blue Hell
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PostPosted: Tue Jun 23, 2020 3:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

It seems the APO signal has to do it .. so I'd trace that one to T8 and see where it differes from the working one.
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Jan
also .. could someone please turn down the thermostat a bit.
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