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help with vc divider

2003-01-27 by Jeffrey Pontius

Well, today doesn't seem to be my day for building modules. After
building over 20 kits, which have all worked right off or second off
(after finding an obvious mistake or some kind assistance guiding me in
the correct direction), I'm completely baffled by 2 that don't work.
Here is one, and I hope someone can suggest some direction.

I have 2 vc dividers. The first I put together worked right off. The
second one refuses to respond. That is, when I start on Ken's trimming
instructions there is no output from HO. I've checked that I'm getting
the correct voltage into the pcb, I switched the 4024 and 40106 from the
working divider to the nonworking divider, I've compared the two to match
up every component (and orientation), and triple-checked soldering
connections - no improvement. Any suggestions? Please keep in mind that
I'm extremely poor at electronics troubleshooting - just using my
multimeter correctly gives me a sense of accomplishment :-).
Jeff

Re: help with vc divider

2003-01-29 by John Loffink

Suggestions:

1) Look for open traces or cold solder joints (hazy looking solder).
2) Check power and ground going to all 4 chips with PCB powered. Also
verify 9 volts from the 7809.
3) Check the IC socket connections with the ICs inserted and PCB
unpowered. Do the IC pins really connect to the PCB trace underneath?
4) Beyond this, an oscilloscope starts becoming real handy. You could
try comparing each op amp stage output between the working and
nonworking modules with your multimeter. Use DC volts mode first, then
AC mode for a rough computation of whether any pulses are coming out of
that stage. This might let you narrow it down to the broken section.

I hope this helps.

John Loffink
jloffink@...

Show quoted textHide quoted text

> I have 2 vc dividers. The first I put together worked right off. The
> second one refuses to respond. That is, when I start on Ken's

trimming

> instructions there is no output from HO. I've checked that I'm

getting

> the correct voltage into the pcb, I switched the 4024 and 40106 from

the

> working divider to the nonworking divider, I've compared the two to

match

> up every component (and orientation), and triple-checked soldering
> connections - no improvement. Any suggestions? Please keep in mind

that

> I'm extremely poor at electronics troubleshooting - just using my
> multimeter correctly gives me a sense of accomplishment :-).
> Jeff
>

Re: help with vc divider

2003-01-29 by Scott Stites

Excellent suggestions, all.

If I understand the original post correctly, you are also in the fortunate
position of having one working board.

If you're still no closer to the answer after trying John's suggestions, you
could try a side-by-side comparison of the two boards. You could start at IC1A
and work backward from there, depending on where you get different measurements
between the two boards. An O-scope would indeed be most helpful here, though
sometimes even voltage measurements might tell you something. Also, resistance
measurements with an ohmmeter without power applied to the boards have helped me
in situations like this.

For example, I just finished up a keyboard encoder, everything worked fine except
the octave switch. Looking at the diode gap of a switching diode quickly told me
where the problem was, but not what it was (that took *another* visual
inspection) - an ever so small wisp of solder was bridging two pins of an adder
IC.

BTW, I think I only live a couple of hours from you, Jeff (I'm in Mount Hope,
Kansas). I was born in Manhattan, the son of a K-State graduate and staunch
Wildcats fan.

Good luck and hope you get it working soon!

Best Regards,
Scott Stites

Show quoted textHide quoted text

>On Wed, 29 Jan 2003, "John Loffink" wrote:

>
> Suggestions:
>
> 1) Look for open traces or cold solder joints (hazy looking solder).
> 2) Check power and ground going to all 4 chips with PCB powered. Also
> verify 9 volts from the 7809.
> 3) Check the IC socket connections with the ICs inserted and PCB
> unpowered. Do the IC pins really connect to the PCB trace underneath?
> 4) Beyond this, an oscilloscope starts becoming real handy. You could
> try comparing each op amp stage output between the working and
> nonworking modules with your multimeter. Use DC volts mode first, then
> AC mode for a rough computation of whether any pulses are coming out of
> that stage. This might let you narrow it down to the broken section.
>
> I hope this helps.
>
> John Loffink
> jloffink@...
>
> > I have 2 vc dividers. The first I put together worked right off. The
> > second one refuses to respond. That is, when I start on Ken's
> trimming
> > instructions there is no output from HO. I've checked that I'm
> getting
> > the correct voltage into the pcb, I switched the 4024 and 40106 from
> the
> > working divider to the nonworking divider, I've compared the two to
> match
> > up every component (and orientation), and triple-checked soldering
> > connections - no improvement. Any suggestions? Please keep in mind
> that
> > I'm extremely poor at electronics troubleshooting - just using my
> > multimeter correctly gives me a sense of accomplishment :-).
> > Jeff
> >
>
>
>
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Re: help with vc divider

2003-01-30 by Jeffrey Pontius

Since I've recently had a number of suggestions, I think I should let
those interested know that I found the problem, and (rather
embarrassingly) it was a relatively simple (simple, I suppose, since I now
know what it was) mistake.

Show quoted textHide quoted text

>
> If you're still no closer to the answer after trying John's suggestions, you
> could try a side-by-side comparison of the two boards.

This was the key after several comparisons. I found that I had mistakenly
put in a wire link where Ken had legended a capacitor (the "unassigned
capacitor") near, I think, an LM358. The other pcb did not have the link,
so that one worked ok.

>
> BTW, I think I only live a couple of hours from you, Jeff (I'm in Mount Hope,
> Kansas). I was born in Manhattan, the son of a K-State graduate and staunch
> Wildcats fan.
>

Interesting (I'll have to look up Mount Hope on a map - this is the sixth
state I've lived in). Manhattan is nice as a mid-west college town. At
least we have a lot of (real) hills, trees and water.

> Good luck and hope you get it working soon!

Thanks, Scott. It is working and mounted - now to find out what it can
really do.
Jeff

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