CD4514 Issues with pulses

Discussion in 'Analog & Mixed-Signal Design' started by gface83, May 12, 2018.

  1. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    Hi All

    I'm having a really annoying issue with a CD4514 ic. I have completed a project for an analogue 16 step sequencer. The pulses that control the LED's is the CD4514, but, its doesn't seem to be performing as expected. When I first powered the unit up I was having issues with LED 4 and 10. LED 4 would not light up at all and LED 10 would sometimes work, others it would flicker and other times not come on at all. After doing some continuity testing and realising that everything seemed fine, I decided to replace the LED, switch and diodes on those two channels. After doing this everything worked great, but when I started it up the next day the issue has moved to LED 9 and 16, the exact same problem. So I decided to do some more testing with the oscilloscope and realised that when I'm probing pin 17 which is LED 9 I get a low to high signal, (as expected), but I also get a low to high when the sequencer reaches step 16, and I get the same when I probe pin 15 (LED 16), it gives 2 signals, one on LED 9 and one on LED 16. This must have been what was happening with LED 4 and 10 but didn't measure them with the scope at the time. I have tried replacing the switch, LED and diode on 9 and 16 but it didn't work like last time.

    Can someone please have a quick look at the circuit and let me know If i'm looking in the right place or could it be something else causing the problem. Any help would be greatly appreciated.

    Thanks
     
  2. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Are you allowing enough settling time between setting up the data inputs to the IC and taking the strobe pin low?
     
  3. gface83

    Thread Starter Member

    Jul 16, 2016
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    1
    Thanks for replying. I did not come up with the design, its by Ray Wilson from MFOS and he has built and tested a number of these so everything should work as is. Fortunately, I have managed to fix the issue by replacing the whole switch, LED and diode again, (twice because it didn't work the first time), but, unfortunately this doesn't tell me what the problem was to begin with and I like to learn from mistakes. Now, on to the next issue lol

    Thanks again.
     
  4. Sensacell

    Moderator

    Jun 19, 2012
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    What is it? what's it supposed to do?

    It's hard to imagine fixing something when I have no idea of it's desired function.
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    16 Step Sequencer (+/-9V to +/-15V).
     
  6. Sensacell

    Moderator

    Jun 19, 2012
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    Ok got it now! very cool device, but all that hybrid RC delay logic is tricky to debug unless you really know what's going on there.

    Maybe post a video of the undesired behavior to give a clue as to what's going wrong.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    Try to increase the values of C1, C3, C7, C8 from 0.01uF to 1uF.
    Try to use CD4093 to replace CD40106 and some diodes and resistors.

    seq16schematicpage1_ScottWang.png

    Framed the CD40106 in the original circuit.
    seq16schematicpage1-m1.png
    Source.
     
  8. DECELL

    Member

    Apr 23, 2018
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    So 70's!
    You could program an Arduino to do all of page one and page two and with lower tempo drift too.

    I'm GENX and I'm so glad thats all over!
     
    gface83 likes this.
  9. Sensacell

    Moderator

    Jun 19, 2012
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    Haha Agreed.

    It's a special punishment for those who desire it.
     
    gface83 likes this.
  10. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    Thanks for all the suggestions guys. Unfortunately, it isn't working again. Everything was working fine for an hour then I turned it off and came back to it 2 days later and back to square one, but, now it LED 5 that isnt working and I'm not getting gate outputs on some now (see video), which wasn't happening before. This is a tried and tested design so I cant see what is going wrong. when I
     
  11. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    observe pin 7 on the CD4514 it never goes low and is interacting with every other pin. Ive replaced the chip and had the same results so I really can't figure this one out. I'm about to give up as Ive been working on this for over a month now. Anyway, if you can have a look at the video and see if anyone can figure this problem out.

    Edit: it won't let me upload videos, can someone suggest how I also do this?
     
  12. eetech00

    Senior Member

    Jun 8, 2013
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    Hi

    One thing I noticed is there are no bypass caps across each chip power supply pins shown on the schematic.
    The should be a 0.1uf cap across the power supply pins of each chip. This is standard practice. Otherwise, erratic operation can result...

    eT
     
  13. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    Hi eT thanks for the reply. There is actually a third page of the schematic that includes the bypass caps, I didn’t post that one because it’s just the random generator part of the circuit which is working fine. There is actually an analogue board part of the circuit to which controls the CV and a Vari clock circuit which uses a D-A converter to vary the length of each step, I haven’t included that either. If anyone would like to take a look at them I can post them. The only reason I haven’t is everything seems to be working on those boards.
     
  14. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    Hi Scott thanks for the suggestions. I’ve actually gone a bought the kit to build this circuit PCBs, panels and components from a company called soundtronics in the UK. They have built quite a few of these and said they’ve never had any problems. They are just terrible at providing solutions. They asked me to send them some pics and never got back to me. I’ve emailed them 3 times since. Out of interest would the 4093 fit in to a Cd40106 socket? And what would be the benefit of replacing them?
     
  15. gface83

    Thread Starter Member

    Jul 16, 2016
    74
    1
    Hi DECELL I decided to build this to go with my analogue synth that I made. I want to keep everything as analogue as possible, even though there’s all sorts of issues that accompany it like tuning it. That’s a bit tedious ha!! I’ve got enough digital synths and VST synths just wanted something to actually play with. Out of interest, what is GENX?
     
  16. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    The capacitors on page three are not the bypass capacitors for each chip.

    a) They are not located near any IC power pins.
    b) There are not enough of them - 8 chips, 4 caps.

    Also, on the board layout it is clear that there are no close-in decoupling capacitors near any chip.

    Each low power logic chip - 0.1 uF ceramic, as close as possible to the Vcc or Vdd pin, with the shortest possible lead length to the ground pin.
    CD4514 - 1.0 uF ceramic, same placement rules. Larger capacitor because this chip is the LED driver and switches larger currents.
    Opamps - 0.1 uF ceramic and 10 uF electrolytic in parallel from each power pin to GND.

    The lack of decoupling capacitors is a significant statement. I get that the board works, but that is not the same as being well-designed. The layout is ... inexperienced. If the project cannot afford the cost of a 4-layer board with a ground plane, at least fatten up the GND traces. Is there an image of the other layer routing?

    ak
     
  17. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    It would fit the socket but the pinout is very different. The 4093 is a quad Schmitt NAND package. The 40106 is a hex Schmitt inverter package.
     
  18. ScottWang

    Moderator

    Aug 23, 2012
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    I bought many kits to play with over twenty years ago, some of them are still working fine as the power supplies and that is one kind of learning, and the experienced of kits was not so good, but they caused me to grew up, because the kits had many problems, but I tried to fixed them to be normal and leart the theories from the different kit.

    They are all 14 pins, but it is for the different design with the same theory, the CD4093 can fit in the socket of CD40106, but you can't put a CD4093 into the socket of CD40106 in your board.

    Less components less problem, reduces the size of PCB, that is the personal behavior to use more less components.
     
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