Formant elektor VCO's

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Ok so i fried my VCOs Evil or Very Mad

I had some other stuff hooked up the wrong way, power wise to the power dist. bus and things went weird.

I am getting waveforms on all outputs, and all tuning pots etc react.
The thing is that the tuning is now CRAZY unstable. Just as if you pitch modulated the vco with a noise source.

This is what i did so far with no luck:
Changed the following:
IC1
IC2
IC3
IC4
T1
I would like to swap out T2 and T3 but they are BF245 A/B's and i can't find them anywhere. Is there a substitute?

Here are some pictures of the schematics. I didn't include wave shapers etc, just the parts that i might suspect could be the culprit.

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

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

Thanks a million!!!!!

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

someone save me!!!!!!! Sad

wackelpeter · Posted: Fri Apr 03, 2015 12:26 am Post subject:

one simple question... have you checked the voltages are correct now... the +/-15 Volts are okay and the +5V too???

if there are some Regulators involved in the +5V i think they are not so happy when powered up the wrong way and could die.....

a Substitute for the bf245 is from what i've read the j113 or PN4393

here's a link sorting out the differencies and common in characteristics of those... unfortunately only in german...

http://www.elektronik-kompendium.de/public/schaerer/anasw1.htm

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Thanks!

I just can't find those transistors in Denmark though (the ones you link to) but maybe I can order them from somewhere else.
The 5 volt supply works fine.

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Ok. so i found them now and ordered them. Could something be wrong with my 5v supply even though it actually reads 5v? i mean could it be untsable somehow. Im measureing with a digital voltmeter.
Thanks:)

wackelpeter · Posted: Sat Apr 04, 2015 8:29 am Post subject:

you should measure that also with an Digivoltmeter...

But as we are at it... measure the normal power rails too if you haven't done that already... i now remember that i had a Problem once with unstable oscillators in one of my synth cases too...

that was caused by a small voltage drop 10mV or so on my power rails whenever one of my dividers LED was on...

so maybe it's something in that vein... anything on your board could be blown or working incorrectly because of the misconnectecd power rails and now is causing that voltage Drops... perhaps you have already measured that... otherwise that would be an other idea...

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Just measured directly on the psu with nothing else attached. 5volt is solid. (Although it's 5.5v but I think it's been like that forever). So I'm guessing it's the 2 transistors I mentioned earlier. Something is mucky around the cco and it fits with the transistors being dead in that area. I'm just waiting for the mailman now:)

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Ok. So tried switching to another psu and now it's almost working. It's oscillating but the coarse tuning knob does almost nothing. And the fine tuning knob does nothing. Seems like the knob "sensitivity" is off. I'm thinking t1 could be the culprit?
Anywhere else?
Thanks:)

the19thbear · Joined: Apr 19, 2007 Posts: 151 Location: denmark

Fixed! Thanks:) Turned out that in the process of finding the error i put in one of the ICs the wrong way;)

A new PSU and turning the IC=succes