[sdiy] little followup, WAS RE: FW: Synthasystem Frequency Divider trouble shooting

[David Ingebretsen]

I just fired up the circuit and confirmed when the base of Q20is shorted to
ground I get a reset.

And, it I hit the base of Q19 with +12, I get the expected reset pulse
independent of how long I hold it positive and it resets all the flip flops.

Why aren't the AND gates sending a pulse to the base of Q19?

David

~~ -----Original Message-----
~~ From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
~~ bounces at dropmix.xs4all.nl] On Behalf Of David Ingebretsen
~~ Sent: Saturday, November 13, 2010 10:41 PM
~~ To: 'Oren Leavitt'
~~ Cc: 'sdiy DIY'
~~ Subject: Re: [sdiy] FW: Synthasystem Frequency Divider trouble shooting
~~ 
~~ Hi Oren,
~~ 
~~ It's a non-shorting contact.
~~ 
~~ I don't see how that would matter though once the switch is moved.
~~ 
~~ I don't think turning the switch is what is supposed to reset the flip
~~ flops. It's when the discrete AND gates are active. For example, on a
~~ divide
~~ by 5, setting the switch to "G5", when Q4 and Q6 are "ones", the AND gate
~~ formed with these two signals makes the AND gate high and in theory
should
~~ somehow reset the flip flops so they can count to 5 again. Similar for
the
~~ other "divide by" settings.
~~ 
~~ Thanks for having a look.
~~ 
~~ David
~~ 
~~ 
~~ ~~ -----Original Message-----
~~ ~~ From: Oren Leavitt [mailto:obl64 at ix.netcom.com]
~~ ~~ Sent: Saturday, November 13, 2010 10:21 PM
~~ ~~ To: David Ingebretsen
~~ ~~ Cc: 'sdiy DIY'
~~ ~~ Subject: Re: [sdiy] FW: Synthasystem Frequency Divider trouble
shooting
~~ ~~
~~ ~~
~~ ~~
~~ ~~ On 11/13/2010 9:29 PM, David Ingebretsen wrote:
~~ ~~ > Hi group.
~~ ~~ >
~~ ~~ > I'm trouble shooting the Synthasystem Frequency Divider prototype
~~ PCB.
~~ ~~ Since
~~ ~~ > these are all designs which were in actual production, I do make the
~~ ~~ > assumption the original schematic is correct and that my capture may
~~ ~~ have an
~~ ~~ > error. That said, I couldn't find an error and Nyle said it looked
~~ ok.
~~ ~~ The
~~ ~~ > schematic is here:
~~ ~~ >
~~ ~~ > http://www.xmission.com/~dingebre/SP_Freq_Divider_1.1.pdf
~~ ~~ >
~~ ~~ > Nyle's original is here:
~~ ~~ >
~~ ~~ > http://www.xmission.com/~dingebre/SP_Frequency_Divider_0001.JPG
~~ ~~ >
~~ ~~ > The project page is here:
~~ ~~ >
~~ ~~ > http://www.xmission.com/~dingebre/Freq_Divider.html
~~ ~~ >
~~ ~~ > I understand the basic ideas of the circuit and everything seems to
~~ be
~~ ~~ > working except the one-shot in the lower left side.  Basically, the
~~ four
~~ ~~ > Flip-Flops in the middle are a binary counter. The 8 position
~~ "divide"
~~ ~~ > switch is hooked to discrete AND gates which select the denominator
~~ for
~~ ~~ the
~~ ~~ > divide. The way Nyle set it up, you get 3, 5, 7, 9, 11, and 15. The
~~ one
~~ ~~ shot
~~ ~~ > is supposed to fire when you hit the desired count and it should
~~ reset
~~ ~~ all
~~ ~~ > four FFs. The way I see it, the last FF should never even count if
~~ you
~~ ~~ > select a divide by 3 or 5, but it does count. I also never see a
~~ reset
~~ ~~ pulse
~~ ~~ > out of the one shot unless I force it by grounding the base of Q20.
~~ ~~ >
~~ ~~ > The primary symptom is the divide by 11 divides by 7. When I've
~~ looked
~~ ~~ at
~~ ~~ > the scope, the first time I select the divide by 11, it divides the
~~ ~~ first
~~ ~~ > cycle only by 11. Thereafter, it divides by 7.
~~ ~~ >
~~ ~~ > Secondarily, it appears the one-shot is not being triggered,
~~ therefore
~~ ~~ the
~~ ~~ > FFs are not being reset when the count reaches the selected count on
~~ the
~~ ~~ 8
~~ ~~ > position switch.
~~ ~~ >
~~ ~~ > I understand the one shot and simulated it for good measure. What I
~~ ~~ don't
~~ ~~ > understand is how Nyle is resetting it. I thought you need to pull
~~ the
~~ ~~ base
~~ ~~ > of Q20 low. When I do that, it resets.
~~ ~~ >
~~ ~~ > I don't get the little capacitor/diode/resistor connection to the
~~ pole
~~ ~~ of
~~ ~~ > the divide switch.
~~ ~~ >
~~ ~~ > Any thoughts?
~~ ~~ >
~~ ~~ > I've emailed Nyle, but sometimes he takes a few days to answer and I
~~ ~~ hate
~~ ~~ > pestering him.
~~ ~~ >
~~ ~~ > David
~~ ~~ >
~~ ~~
~~ ~~
~~ ~~ Hi David,
~~ ~~
~~ ~~ Does your SP/6T divide switch "break before make" when you change
~~ ~~ position?
~~ ~~ It looks like the one-shot circuit depends on R56 briefly pulling D21
~~ ~~ "high" while the switch wiper is transitioning between contacts. If
~~ your
~~ ~~ switch is a "make before break" type, that will not happen.
~~ ~~
~~ ~~
~~ ~~ - Oren
~~ 
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