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Dual LFO Build Problem [FIXED]
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author Dual LFO Build Problem [FIXED]
I've just completed the build of my Dual LFO. I seem to be having a couple of problems. I knew something was wrong when I powered it up and the LEDs didn't flash. Further testing revealed that while LFO #1 appeared to be working properly LFO#2 had some issues.

I have checked the board for bridged solders and double-checked that all the correct parts are in their correct locations.

I am pretty much a complete novice when it comes to troubleshooting and don't exactly know where to start. If anyone has any suggestions as to where I should look and what I should check I would appreciate it very much.

Here are some pictures of the board itself.

I noticed some voltage differences between the ICs at U2 and U4 when both LFOs are set the same. I will indicate them in a followup post.
The LED problem might be that the LEDs are wired the wrong way around. Simply try the 2-way sockets the other way and see if that gets them flashing.

The weird interaction between LFO2 and LFO1 could be that the LWR connection that joins the main PCB to the socket PCB is wired incorrectly. Instead of pin 1 to pin 1, it's maybe going pin 1 to pin 4, pin 2 to pin 3, etc. Unfortunately, it's difficult to tell on the photo.

Thanks for the quick reply Tony. goes;

You were correct in the assumption that the LEDs were wired backwards. After learning how to correctly read a Diode diagram on the board / schematic I learned that the pointy side of the triangle with the bar is in fact NEGATIVE and not POSITIVE. You may notice that my wiring has the Red wire on the Cathode (-) side as I incorrectly thought it was the Hot side. But wait, it gets stranger....

I did make the assumption that I may have wired the LEDs backwards so I would test the LED in position 1 to test my assumption. It didn't work in either orientation. But here's why; I did a crappy job of soldering in the wires for LED 1. It was, in my opinion, the worst solder joint on the board that I had done. When I changed the orientation of LED 2 and it began flashing while LED 1 still did not I became ultra-suspicious of my solder job. I re-did LED 1's wires and voila! Flashing LEDS (the second coolest part of modulars hihi )

With both LEDs working I started twiddling the knobs and it seems that the problem with LFO 1's knobs affecting LFO 2 may have gone away. I say seems and may because the Dual LFO is only on my workbench and not plugged into the modular for full testing. I will test the Dual LFO later today and post my results.

Finally, I'm including a photo of the 4-wire cable for the Socket6 board for your examination. You'll note that the connector on the left is inverted compared to the one on the right and the wires all run straight to their respective ports. When held in the same orientation it appears to me that 1 goes to 1, 2 to 2, etc... Please let me know if I am correct in my assumptions.

Thank you again for your prompt and sage advice. As a rookie the most terrifying part of building is figuring out where I may have gone wrong. Not knowing how to begin looking for a problem is the worst part. I really appreciate your help!
The LED thing is an easy mistake to make. Thankfully, most LEDs can take being wired up backwards for some time without damage.

That LWR interconnect is made correctly so that wasn't the cause of the other problem.

Thanks again Tony.

I'm not 100% sure things are working correctly still. I believe there's still some bleed-through from LFO 1 to 2.

The thing is, though, I don't think I'm in too much of a hurry to fix it. The effect is sort of cool and I've got a handle on controlling it. It has yielded so very interesting sounds. Further, it makes my Dual LFO one of a kind in a way.

I'll make a video of the effect I'm getting and post it on this thread later today.

Thank you again for your support!
Fixed it!!

While building a second Dual LFO I discovered the problem with this one; wrong capacitor values. I mistakenly used .1uF caps in C13 and C14 rather than .001uF.

I replaced the caps with he correct values and voila... working perfectly!

While the unit worked with the wrong caps, turning the speed knobs below the 12:00 position pretty much stopped oscillation.
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