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 Forum index » DIY Hardware and Software » Thomas Henry designs
TH VCO1 - only triangle working?
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creekree



Joined: Mar 30, 2006
Posts: 192
Location: Morgenland Neukölln
Audio files: 1

PostPosted: Wed Apr 15, 2009 7:50 am    Post subject:  TH VCO1 - only triangle working?
Subject description: SOLVED!!! ...also: UNIVERSE, YOU GOTTA BE KIDDING ME!!
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hi all,

after a long period i found some time to finish my TH VCO1.
however, i can only get the triangle wave to work.
i triple-checked my wiring, and everything seems to be in order.

i have to point out that i substituted the CA3080 with a LM13700 - but i am pretty sure that is not the problem, as the triangle part works.
also i substituted the TL072`s with 4558`s, but i have done so in different circuits before and all those worked fine (i just happen to have a lot of 4558s and no TL072`s, that`s the only reason why i did it).

where do i start troubleshooting?

thanks in advance!

christian

Last edited by creekree on Thu Apr 16, 2009 11:53 am; edited 1 time in total
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creekree



Joined: Mar 30, 2006
Posts: 192
Location: Morgenland Neukölln
Audio files: 1

PostPosted: Thu Apr 16, 2009 11:47 am    Post subject: SOLVED! also... UNIVERSE, YOU GOTTA BE KIDDING ME!!!!! Reply with quote  Mark this post and the followings unread

first of all... the VCO is working now. at this very moment i listen to elusive sine and pulse waveforms - something that i apparently was not doing before.
let me explain. this is a story of despair, grief and extended brooding over schematics. but it also is a story of not giving up, of hope and the joy of finding a solution - NO MATTER HOW STUPID IT IS.

what it boils down to: i simply couldnt figure out why i wouldnt get any sine or pulse wave. i checked my wiring, then re-checked it over and over again. i changed all of the ICs, then i changed the transistors (well, you never know, right?), but to no avail.
i then very closely inspected the circuit board - any hairline cracks? etching faults? i pride myself to be able to malke quite decent toner transfer PCBs, and i couldnt find any flaw on this one.
next i reheated some solder blobs that looked a little "cool"... you get my drift. i checked everything i could, but there simply was nothing wrong.

i looked over the schematics again and read scott stites VCO1 website again and again... i was pretty much fed up with the whole shebang and wanted to put it away, never to surface again.

i then had the idea to randomly probe around on the pcb - and all of a sudden i was able to a sine wave at pin 6 of IC3! but wait... why cant i hear it at R6?
same thing with pin1 of IC4 and R12 - the signal just magically disappeared after the resistor!

having gained new hope i started to examine this strange behaviour.

i dont recall every combination of things that i did nor do i intend to write it all down, but in the end i more-or-less accidentally found the culprit:

THE JACKS THEMSELVES!

those dirty bastards have a short between their lugs!
I MIGHT AS WELL HAVE PUT A WIRE LINK BETWEEN THE OUTPUTS OF THE OSCILLATOR AND GROUND!

the pcb itself - perfect
the wiring - correct
the components - perfect
the jacks - pieces of utter crap

look at the blurry pic - there is continuity between the tip and ring terminals of the jack! WTF?!?!?!?!
...all in all three of them had this fault. i bought them some time ago, they have never been used, they are brand new, so to speak.


i dont know - there probably is something to learn from all this, but i just cant figure out what exactly this might be.


IMAG2941.JPG
 Description:
it looks so innocent, but this jack is the devil! THE DEVIL I SAY!!!! (sorry for the picture quality, by the way)
 Filesize:  487.93 KB
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IMAG2941.JPG


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fluxmonkey



Joined: Jun 24, 2005
Posts: 708
Location: cleve

PostPosted: Thu Apr 16, 2009 1:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

i once spent a whole evening troubleshooting something... checked all the hard stuff... only to find out i'd wired up all my jacks to the switching connection, not the tip. doh.

oh well, at least i won't make that stupid mistake again. i'll make some other stupid mistake.
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BananaPlug



Joined: Jul 04, 2007
Posts: 307
Location: Philly
Audio files: 5

PostPosted: Thu Apr 16, 2009 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Another reason to go bananas!
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