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 Forum index » DIY Hardware and Software » Jürgen Haible designs
JH Varilogic problem
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AnalogCustom



Joined: Jun 23, 2009
Posts: 52
Location: Chile

PostPosted: Thu Sep 03, 2009 12:02 am    Post subject: JH Varilogic problem Reply with quote  Mark this post and the followings unread

Hello:
Transistors in red circle, very hot.
If input A = High and B = Low, both LEDs are ON.
Equally If input A = Low and B = High, both LEDs are ON.

What will be the problem?

The model used is:

2N4401 (NPN)
2N4403 (PNP)

Thank you.

Marco.


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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Thu Sep 03, 2009 2:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Wrong pinout?

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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AnalogCustom



Joined: Jun 23, 2009
Posts: 52
Location: Chile

PostPosted: Thu Sep 03, 2009 8:20 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Wrong pinout?

JH.


Hello:
Pinout is correct.

I attached a new file

Thanks.

Marco


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jhaible



Joined: May 25, 2007
Posts: 2014
Location: Germany
Audio files: 24

PostPosted: Thu Sep 03, 2009 9:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Ha, I have an idea. The transistor whose base is switched to GND will go into zener mode when its BE junction is reverse-biased!

Funny I never noticed this in all these years in my JH-3 synth. Maybe a current limit from the on-board regulators prevented heating.

Cure: Put a 1N4148 diode in series with each emitter of these two transistors.

JH.

_________________
"I tell you the truth, if anyone says to this mountain, 'Go, throw yourself into the sea,' and does not doubt in his heart but believes that what he says will happen, it will be done for him. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours." (Mk 11,23f)
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AnalogCustom



Joined: Jun 23, 2009
Posts: 52
Location: Chile

PostPosted: Thu Sep 03, 2009 10:41 am    Post subject: Reply with quote  Mark this post and the followings unread

jhaible wrote:
Ha, I have an idea. The transistor whose base is switched to GND will go into zener mode when its BE junction is reverse-biased!

Funny I never noticed this in all these years in my JH-3 synth. Maybe a current limit from the on-board regulators prevented heating.

Cure: Put a 1N4148 diode in series with each emitter of these two transistors.

JH.


Hello. Thank Very much!! I noticed of overheating for the smell.



I attached a new scheme with diodes.

Now works correctly.

Thanks again for your help.

Marco.


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