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

[nicolas]

Another thing to try would be to momentarily disconnect the switch from R56-D21 while it is running, that should also cause D21 to rise from about 0V to about 6V and that should cause the reset pulse.  If that doesn't happen then I would look very carefully at that network around R53-C24-R57-D21-R56.  Maybe R53 has been accidentally placed as 2.2k or D21 is the wrong way round?  

Are you using the same transistors as the original?  Perhaps try a larger value for C24.

Cheers,
Nicolas


--- On Sun, 14/11/10, David Ingebretsen <dingebre at 3dphysics.net> wrote:

> From: David Ingebretsen <dingebre at 3dphysics.net>
> Subject: [sdiy] little followup, WAS RE:  FW: Synthasystem Frequency Divider trouble shooting
> To: "'sdiy DIY'" <synth-diy at dropmix.xs4all.nl>
> Received: Sunday, 14 November, 2010, 7:18 PM
> 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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