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 Forum index » DIY Hardware and Software » YuSynth
VC-LFO-2 Not working
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Aottens



Joined: Mar 14, 2010
Posts: 32
Location: The Netherlands

PostPosted: Wed Jun 11, 2014 11:57 am    Post subject: VC-LFO-2 Not working Reply with quote  Mark this post and the followings unread

Hello I've just build the VC-LFO-2. Only problem is, I am not getting it to work. In the first place, the yellow led does nothing, checked the wires, all good. I'm only not sure about the DPDT switch. I really think I've connected it wrong, could it be that I've placed the switch upside down? Does it make any change?

Checked the alignment of the IC's, all good. 1 little question, tje 1uF cap, does it need to be a tantulum? No I've used a polyester film version. It didn't say it had to be a tantulum in the BOM. I will upload some pics asap!

Thanks in advance for the help!
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capicoso



Joined: Nov 19, 2012
Posts: 128
Location: Argentina

PostPosted: Thu Jun 12, 2014 12:34 am    Post subject: Reply with quote  Mark this post and the followings unread

did you calibrate it?
When I built it I thought it wasn't working, the led wouldn't light up, nothing. I had one error near 7555 and lm741, after fixing that, still the same... Ihad one of the multiturn trimpots way low, and the frequency was loooooow, started calibrating it and it worked.
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Aottens



Joined: Mar 14, 2010
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Location: The Netherlands

PostPosted: Fri Jun 13, 2014 2:31 am    Post subject: Reply with quote  Mark this post and the followings unread

That could be a logical explanation! I did not calibrate it yet. Tried to, but the scope wasn't showing me a sawtooth only once. This was on the 1x setting on the DPDT switch. So the question also is, does C1a really needs to be a tantalum? Yves doesn't say it in the B.O.M. but he does say it in the calibrating proces. Still a little bit confused over here :S

I am not really familiar with oscilloscopes so can you tell me what settings to use on the scope?
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isak



Joined: Dec 13, 2009
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PostPosted: Sun Jun 15, 2014 4:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there.
From the pics of the people who build this unit it dosnt have to be tantalum cap.
My guess is that Yves meant C1b when he said "make sure it's tantalum....."
Look at the pics of the boards:
http://yusynth.net/Modular/Commun/LFO/GALLERY/zarko-VCFLO2-b.jpg
http://yusynth.net/Modular/Commun/LFO/GALLERY/Sebo-LFO2-back.jpg
In the next link the cap is ceramic..
http://yusynth.net/Modular/Commun/LFO/GALLERY/Sbrenner-LFO_b.jpg

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Aottens



Joined: Mar 14, 2010
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PostPosted: Wed Jun 25, 2014 3:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Found a small problem in my PCB. I've got the led working right now, and my scope shows a sinewave on the saw output. What could be the problem?
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Aottens



Joined: Mar 14, 2010
Posts: 32
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PostPosted: Mon Dec 22, 2014 3:28 am    Post subject: Reply with quote  Mark this post and the followings unread

It's strange, but I can't seem to get it calibrated correctly, here are some pictures of the PCB. Can someone spot any errors?

https://www.dropbox.com/s/dytjkg7mg7ixerp/2014-12-22%2010.38.17.jpg?dl=0
https://www.dropbox.com/s/v2cbwcmvhbthbpn/2014-12-22%2010.39.26.jpg?dl=0
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Aottens



Joined: Mar 14, 2010
Posts: 32
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PostPosted: Fri Jan 09, 2015 1:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

No one?
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Aottens



Joined: Mar 14, 2010
Posts: 32
Location: The Netherlands

PostPosted: Tue Apr 18, 2017 1:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Allright, this thing is still not working.

Did some testing today. I don't have any of the outputs working. Tested if all the chips where getting their power supply, they do. They all get the desired power.

If I look at the schematics I can see that on pin 1 of U2 I need to have a saw, correct? Well, no saw over there. Strange! So no waveshaping happening at all.

Problem is, this is kinda where my troubleshooting capabilities stop. Could you guys give some tips on where to look next? I think I already narrowed it down quite a bit.

Thanks in advance!
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gdavis



Joined: Feb 27, 2013
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PostPosted: Tue Apr 18, 2017 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes, U2 pin 1 should have a saw. U2 pin 7 should have a ramp (inverted saw).

You can also check:
U2 pin 5 for a ramp
U2 pin 6 is connected to/same voltage as pin 7.
Q1 emitter is +15V
U4 pin 6 voltage moves inversely to rate voltage (when rate voltage goes up, pin 6 should go down).
U4 pin 3 is close to 0V

You can also try removing Q2

Is there an error in the PCB where the black wire is? Where did you get this board? It looks commercially fabricated, not hand etched.

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yusynth



Joined: Nov 24, 2005
Posts: 1290
Location: France

PostPosted: Tue Apr 18, 2017 11:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

Check with a scope that you get a ramp at pin 2 of U1. It is where the ramp is generated. If there is no ramp here it is no use to search other points of the circuit.
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Aottens



Joined: Mar 14, 2010
Posts: 32
Location: The Netherlands

PostPosted: Mon Apr 24, 2017 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, this issue has been resolved. Found out that a bad 7555 was the issue. Ordered a new one, everything started working. Got everything trimmed and all is looking good!

Thanks for all the help guys.
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