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hububalli
Joined: Feb 15, 2014 Posts: 41 Location: UK
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Posted: Sat Apr 07, 2018 6:40 am Post subject:
SOLVED - ADSR V2 - LED constantly lit |
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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
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Posted: Sat Apr 07, 2018 12:00 pm Post subject:
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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
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Posted: Sun Apr 08, 2018 8:32 am Post subject:
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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?
Thanks for the help, |
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gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
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Posted: Sun Apr 08, 2018 10:43 am Post subject:
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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 |
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hububalli
Joined: Feb 15, 2014 Posts: 41 Location: UK
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Posted: Tue Feb 05, 2019 3:06 pm Post subject:
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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 Posts: 1294 Location: Netherlands
Audio files: 30
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Posted: Tue Feb 05, 2019 3:50 pm Post subject:
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are you sure you have the led connected the right way? _________________ my synth |
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hububalli
Joined: Feb 15, 2014 Posts: 41 Location: UK
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Posted: Tue Feb 05, 2019 4:05 pm Post subject:
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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
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hububalli
Joined: Feb 15, 2014 Posts: 41 Location: UK
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Posted: Sat Feb 16, 2019 8:43 am Post subject:
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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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