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 Forum index » DIY Hardware and Software » YuSynth
SOLVED - ADSR V2 - LED constantly lit
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hububalli



Joined: Feb 15, 2014
Posts: 41
Location: UK

PostPosted: Sat Apr 07, 2018 6:40 am    Post subject: SOLVED - ADSR V2 - LED constantly lit Reply with quote  Mark this post and the followings unread

So on to the next module! The module appears works fine but there is a constant 2.5v at pin 7 of U2, the TL074, so the LED is constantly partially illuminated. When the gate is triggered the LED does respond as expected.

There is a constant +- 100 mV at the outputs when the gate is not triggered if that is of any use. When you manually trigger, you can see the ADSR stages on the outputs on the scope fine.

Any suggestions as to what I should check? Thanks,

Last edited by hububalli on Sat Feb 16, 2019 8:43 am; edited 1 time in total
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gabbagabi



Joined: Nov 29, 2008
Posts: 651
Location: Berlin by n8
Audio files: 23

PostPosted: Sat Apr 07, 2018 12:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey you,
please post always a direct link to the schematic you are talking about
i guess it is that?:
http://yusynth.net/Modular/Commun/ADSR/ADSR-V2-sch.gif

are u are shure u are measuring positive 2,5V at pin 7 of U2? or negative?

can you disconnect R22 at pin 6 of U2b and connect one channel of ur scope there at R22
second channel at pin3 of te 555 (gate)
and post a photo of that two signals?

to the 100mV we could say it is noise

cu tomorrow
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hububalli



Joined: Feb 15, 2014
Posts: 41
Location: UK

PostPosted: Sun Apr 08, 2018 8:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello again g.gabba,

This is the schematic I used, which matches the PCB.

http://yusynth.net/Modular/Commun/ADSR/ADSR555-FINAL.gif

You are right, it is -2.5 V.

I disconnected R18 at pin6 of U2b and connected my scope to the free end of R18, is that what you wanted?

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Thanks for the help,
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gabbagabi



Joined: Nov 29, 2008
Posts: 651
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PostPosted: Sun Apr 08, 2018 10:43 am    Post subject: Reply with quote  Mark this post and the followings unread

yesssss, this is how we work,

now we know that your circuit is working well (as far as i can see imo)
up to the end of R18.

Now connect Pin6 to GND.

then measure
Pin 5,6 and 7 also with the scope, in case there is some weird noise.
please measure on the pins of the IC not on the solderpoints,

cu Smile
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hububalli



Joined: Feb 15, 2014
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PostPosted: Tue Feb 05, 2019 3:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello again!

So finally got round to testing, with Pin6 going to GND. I have nothing on the scope for Pin 5 and 6. I do have -3.1 V at Pin 7.

I find those results very confusing! Does not make sense to me looking at the schematic.
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Grumble



Joined: Nov 23, 2015
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PostPosted: Tue Feb 05, 2019 3:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

are you sure you have the led connected the right way?
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hububalli



Joined: Feb 15, 2014
Posts: 41
Location: UK

PostPosted: Tue Feb 05, 2019 4:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

I did think that but have triple checked and it is as per the schematic.

Interestingly I just connected the front panel to a second ADSR PCB I made and am getting the exact same problem. ADSR seems to function correctly but there is a constant -2.5 V to the LED from pin 7 of U2.
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flagada



Joined: Dec 15, 2016
Posts: 39
Location: Amsterdam

PostPosted: Wed Feb 06, 2019 7:55 am    Post subject: Reply with quote  Mark this post and the followings unread

I vaguely remember having the same problem with this adsr. Maybe this can help to solve your problem?
https://www.muffwiggler.com/forum/topic-179785.html&highlight=
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hububalli



Joined: Feb 15, 2014
Posts: 41
Location: UK

PostPosted: Sat Feb 16, 2019 8:43 am    Post subject: Reply with quote  Mark this post and the followings unread

flagada wrote:
I vaguely remember having the same problem with this adsr. Maybe this can help to solve your problem?
https://www.muffwiggler.com/forum/topic-179785.html&highlight=


Thanks for the tip, I put an 18k across the led and it has gone out.

Interestingly, I think I had two problems going on. I replaced the TL074 for one from a different batch. While R18 was removed as described above, the led was off, which was an improvement. So it seems there was a problem with the previous TL074's I tried. As soon as I put R18 back in though, the LED came on. This matched the discussion on MuffMiggler, and hence fixed by the parallel resistor.
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