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scriptstyle

Joined: Jan 22, 2008 Posts: 250 Location: nj
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Posted: Thu Apr 16, 2009 9:57 pm Post subject:
trouble shooting xrvco/lfo |
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so i stuffed 2 xrvco/lfo pcbs acouple months[these are the bug-brand layouts]. this was before i knew that the resistors i bought off ebay where fake resistors from sure electronics. to make matter worse i used single turn trims all the way around except for one that called for a single turn. i just kinda through them together with stuff i had laying around hoping more then anything that they would make 2 nice vclfo's.
so i finished wiring up the first one. initial testing gave me nothing.. then i noticed i totally forgot the .22uf mylar between the jack and pot, and also found a solder bridge on the pcb
so after i caught those 2 mistakes i hooked everything back up and now i have a high frequency osc(i think) out of the tri/sine out. nothing out of pulse yet. i only had a minute to check it. only the shape pot seems to be doing anything to the signal. at this point im thinking i fried some ic's. Should i swap?or does someone have any suggestions? thanks |
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scriptstyle

Joined: Jan 22, 2008 Posts: 250 Location: nj
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Posted: Sun Apr 19, 2009 10:05 pm Post subject:
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updated had a little time today swapped the tl074 and did a better first run.
i now have a square, and tri/sine.
my exact problems are,
1. my shape pot works but once it gets to about 60% the oscillator goes very high in freq/pitch? im not really sure what its doing there im yet to hook up to the scope.
2. my fine and coarse controls do not do anything...
3. when i moved the Linear fm pot the oscillator changed in sound. nothing was connected to the input??
im really wondering if the shitty components are causing some of the weirdness im experiencing. like i said in my first post i did sub in single turn trims [i haven't even had the time to give the trims adjustments], and used the junky ebay resistors from sure electronics.
4. what resistor values are the ones that need to be closer to ideal? maybe i could switch out a couple of the more important ones?
next up on the list for me is changing the lf442 since this was the ic closest to the solder bridge. then hookup the scope and do some trimming.
the fact that my fine and coarse pots are not working really has me bummed.
thanks to anyone who can shed some light to a guy who needs to pull some time out of his pocket! |
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scriptstyle

Joined: Jan 22, 2008 Posts: 250 Location: nj
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Posted: Wed Apr 22, 2009 1:58 am Post subject:
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| I'm super puzzled I had ten spare minutes today poped in a new lf442 and now all I got is a short oscillation followed by a pop, then another short oscillation pop ... All ic's are getting the correct voltages. Hopefully I can get some more time and go poking around with the scope. Maybe I'm having a stray capacitence problem. I clean my boards well, but some may have seeped through the holes and be hiding on top? |
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scriptstyle

Joined: Jan 22, 2008 Posts: 250 Location: nj
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Posted: Sun Apr 26, 2009 7:16 pm Post subject:
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i worked it out today. and made a real dumb mistake when replacing an ic
now i just need to tune it up. i may need change values some where. |
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