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Only one oscillator of cowbell working

Posted: Nov 28th, '14, 10:44
by peristilius
I just finished my Yocto from the first batch this week (there was a long period of rest between start and finish ;) ). But because of my delay I am hoping to get one of those sweet metal cases. :D

First of all I want to compliment Vincent on this amazing project. The kit was carefully put together and the instructions were very clear. This was my first DIY project and I had limited soldering experience, but almost everything seemed to work pretty well the first time I powered up the machine.

There is one significant issue. Only one of the two cowbell oscillators is playing. The one that is tuned by TM2 plays and sounds alright I guess, but the one that is tuned by TM1 remains silent. Now since I don't have any experience with troubleshooting, I thought maybe people here would be able to provide some tips.

I don't have an oscilloscope yet, but I am planning to buy one, although my budget is quite limited, so it would probably be an older second hand analog or a new USB scope. It would be great if I could use it to calibrate the noise voltage as well, since I don't have a RMS meter. I think only digital oscilloscopes can calculate RMS voltage, but since I don't really have experience with this as well maybe someone can tell me what to look for or guide me towards alternatives.

When this is fixed I might want to fine-tune some of the instruments, but at least all the other instruments are playing and sounding pretty much like their 808 counterparts. :)

Your help is much appreciated!

Re: Only one oscillator of cowbell working

Posted: Nov 28th, '14, 17:50
by peristilius
By messing around with an audio cable and audio explorer I found the problem is probably at Q15, so I will replace that and see if it helps. I also found that I can use audio explorer to tune the oscillators, so I probably won't be needing an oscilloscope, just something to measure the noise voltage. :) Both oscillators are tuned too low though, so I will have to replace some resistors as well.

For replacement of Q15 do I just have to get another 2SC945 transistor and I'll be safe?

Re: Only one oscillator of cowbell working

Posted: Dec 1st, '14, 18:50
by peristilius
Okay, upon desoldering I realised Q15 was in the wrong direction, so after turning it around the cowbell worked just fine. :D