16 Step Sequencer Rate Problem

OW · Joined: Nov 03, 2009 Posts: 122 Location: London

Hi,

So I finished building my 16 step sequencer, however I am experiencing a problem with the rate control.

When the rate control pot is at its lowest, the sequencer sequences faster than it should.

As I turn it a quarter way up, there is no change in the sequence rate until I turn it a little more. And the same thing happens on the increased sequence rate.

At some positions of the pot, the sequencer goes through the first two notes quicker than the others.

The External Clock In works fine, as do all other functions. And I am using the Texas Instruments CD40106BE IC.

Does anyone know what's wrong with it?

Any help would be greatly appreciated.

Thanks!

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

Any luck? My guess would be to quadruple check all component values around U1-D, D9, R18, R23 and C10 and make sure the 1 meg rate control is right and wired correctly, and check for solder bridges/missed solders around there.

I can probe around mine if you think it might help, good luck.

OW · Joined: Nov 03, 2009 Posts: 122 Location: London

Still no luck, all components, wiring and solder joints appear to be correct. That would be great if you could probe on yours!

Thank you!

I look forward to hearing from you.

jordroid · Joined: Jan 17, 2010 Posts: 193 Location: ithaca, new york

Sorry for the delayed response, it's the last nice weather of the year here.

I took some DC measurements and scope readings, all voltages are approximate and i am using a +/-12v power supply. Here is some hopefully relevant info, excluding power and grounded pins, which all read correctly:

U3-

-pin 1 sits at about +11.5v when stopped, and 0v when running

-pin 2 sits at 0v when stopped and +12 when running

-pin 3, scope is AC coupled, i see a repeating wave starting at -20mv, jumping to +40mv, discharging down to just above ground in a capacitor discharge fashion, then jumping to -20mv and starting again, in time with the clock as set by the rate control. pin 3 sits at +12v when stopped, and the wave is sitting between around +11.5v to +12v.

U1-

-pin 9, scope is DC coupled, starts at around +3v, charges up to around +8v, discharges back to +3 and starts again, all in a capacitor charge/discharge fashion, in time with the clock. sits at 8v when stopped.

-pin 8, scope is DC coupled, i see a square wave between 0v and +11.75v in time. sits at 0v when stopped

Hope it helps, good luck!

jaidee · Posted: Wed Oct 13, 2010 4:23 pm Post subject:

Hi o-w1

Have you got anywhere with your debugging?

I'm asking pointedly because I've finally got round to completing my build using an Elby parts kit and have come up against exactly the same problem: at the lowest setting of the rate pot,the sequencer spins round at a ludicrously fast rate. Using an external clock steps the sequencer at a sensible and easily adjustable rate. I've checked all of the relevant components for values and soldering and they seem fine.

I'm a "paint by numbers" builder (I can usually follow instructions, put the right component in the right place. but without any real understanding of the underlying theory) and I must admit I'm baffled.

If anyone else has any thoughts or suggestions they'd be much appreciated!

synthmonger · Posted: Fri Oct 15, 2010 1:43 am Post subject:

Are you sure R18 is in place? I'd also check to make sure pin 8 is going to the clock input and not pin 9 or the end of R23.

OW · Joined: Nov 03, 2009 Posts: 122 Location: London

Sorry for the late reply, I've been away at University. I've checked all solder connections and part orientations; which appear to be correct. I haven't got round to testing anything with my meter, but will in fairly soon. Please let me know if you solve this problem, and I will do the same.

I will post and update within the week.

Thanks for all the help so far!

synthmonger · Posted: Fri Oct 15, 2010 4:15 pm Post subject:

I'd try swapping out the 40106 for another brand. It might just be a funky chip. I've had problems with them before.

jaidee · Posted: Sun Oct 17, 2010 4:08 pm Post subject:

Thanks for the help, guys!

I've solved the problem with my build; it was the power supply traces.

The postive supply feeds over the digital board with traces on the top and the bottom of the board. On checking more rigorously than I'd done previously, I found that whereas the components fed from the traces on the bottom were fine, the components fed from the tracks on the top were only getting 5V (I'm using a +/-15V supply).

Turns out there was a defect with the top trace at one point so that barely any power was getting through.

Solution - I carefully sanded off the solder mask at the offfending point and added a solder bridge.

Now works perfectly!

May be worth checking, o-w1, in case there was a bad batch of boards.

OW · Joined: Nov 03, 2009 Posts: 122 Location: London

You solved it! Well done!

Unfortunately I cannot seem to find a voltage drop. Could you please let me know what components have a faulty power supply?

Thanks so much!

jaidee · Posted: Fri Nov 12, 2010 6:06 pm Post subject:

Sorry - it's taken me a while to get back on this.

I've marked on the component layout diagram the parts which are directly connected to the power lines. Tracing back to the poisitve line, the first component connected is the left side of R28. I found that the positive voltage at this component and at all of the relevant pins of the ICs was only about 5V (I am using a 15V supply).

As previously mentioned, on closer insprection I found that there part of the t6race close to the connector was far thinner than it should have been and was in effect acting as a resistor.

Hope this helps!

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