[sdiy] FW: Synthasystem Frequency Divider trouble shooting

[David Ingebretsen]

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