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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS VCO-no output. where should i start checking?
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rjd2



Joined: Sep 02, 2007
Posts: 235
Location: philly

PostPosted: Thu Jan 08, 2009 12:11 pm    Post subject: CGS VCO-no output. where should i start checking? Reply with quote  Mark this post and the followings unread

hi folks, i recently built one of these, and im getting no output at any of the waveshapes. i have a crystal earpiece that i use for audio probing on circuits, which i checked the legs of almost all of the opamps, and didnt get anything audible. where should i start sniffing around, either with a DVM or probing for sound? thanks for the help-rj
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Adam-V



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PostPosted: Thu Jan 08, 2009 5:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi rj,

I haven't built one of these but I can offer you some basic troubleshooting advice.

First off, start with some visual checks:
1. Check your wiring.
2. Check your wiring again.
3. Look for solder bridges on the board (use a magnifying glass if needed).
4. Check component orientation (diodes, transistors, ICs)
5. Check component values against the schematic
6. Check that all of the ICs are correctly seated in their sockets.

Next perform some empirical tests
1. Check that the power rails are all present and correct.
2. Check that power is making its way to the appropriate pins on the ICs etc.

If these basic steps don't reveal the cause of your problem then some more in depth checks will be required (measurements at specific circuit points etc) but someone else will need to help you with that.

Cheers,
Adam-V

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rjd2



Joined: Sep 02, 2007
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PostPosted: Thu Jan 08, 2009 9:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi adam, thanks. i had done ALMOST all of those things initially, but going back over it, i found that pin 4 of the lm394 read 0V. im not totally sure what voltages i should see on what pins, but on any 8 pin chip, im assuming pin 4 is a power pin? all the other opamps read -15V on pin 4, and the lm3900 read +15V on pin 14. sorry, im still kinda green on some of this stuff. thanks for the help.
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andrewF



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PostPosted: Thu Jan 08, 2009 10:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

LM394 is not a normal chip, it is a dual transistor package.
pins 4 & 5 are unconnected. So 0V on pin 4 is ok

it is worth learning the pinouts of chips you are using. usually google will get you there.

What FET did you use?
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Rykhaard



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PostPosted: Fri Jan 09, 2009 7:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Another thing to make sure of on Ken's VCO is that you have every single wire jumper added. It can be easy to look at the board, seeing the white guideline that's showing where the jumper has to go and mistaking it AS a wire jumper. I've made that mistake in the past, myself.

As Andrew had asked, also. Be very carefuly with the FET transistor. Different versions of them CAN have different pin layouts. G, S, D; S, G, D; etc. With them (as well as other transistors) it is also best to download and read the datasheet for them, to see the pinout from them. As well, whether the pinout is shown from looking at the top of the FET, or at the bottom of it.

Also note - the FET and the CA3140 ARE static sensitive. It's best to handle them, making sure that you are Grounded yourself!

With the AC Volts measurement of your digital multimeter, or the probe of an oscilloscope, check pin 6 of the CA3140 to see if there is any signal coming from it. If there is not, it's then possible that your problem is at that chip, or before it.

I currently have 2 of the Ken VCOs to debug, myself. I haven't gone through either of them completely, yet.
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rjd2



Joined: Sep 02, 2007
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PostPosted: Fri Jan 09, 2009 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the help, guys. i didnt realize how easy it was to find the pinouts on an opamp-google needs to be my friend a little more in the future.

so i have found at least one problem: the TL072 that is directly to the left of the lm394 shows -10 V on pin 8. so do several of the lm311's that are on the "lower" side of the board(looking from top).

i traced this, and it looks like it connects to the +15V line, passing thru a 100nf ceramic cap. i have +15 on that rail, but as soon as it hits that 100nf cap, it reads -10V. should i swap the TL072 opamp?

EDIT: i swapped the TL072, its not the culprit. pin 8 of this TL072 ties to a 100nf cap, as well as 1 leg of the 50k "ZERO" trimmer. i am at a loss.
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andrewF



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PostPosted: Fri Jan 09, 2009 6:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

it is probably best to be 100% certain there are no build errors before you start hunting with the multimeter.
from your descriptions, it does sound like a missing jumper wire, or soldering error. Easier to find them visually, the MM will just be confusing.
as Ryk said - there are many jumper wires and it is easy to miss one of them.
this pic on Ken's page helps locate them
Posted Image, might have been reduced in size. Click Image to view fullscreen.

also, 15V dc will not pass thru a capacitor. caps can only pass an AC signal.

Don't worry, you will get there Very Happy
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rjd2



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PostPosted: Sat Jan 10, 2009 2:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks, andrew. i checked all my bridges, polarities, IC values/alignment-everything on the pcb is correct, visually. thru doing more sniffing around, i noticed that something in the module started pulling the -15V down to ground. so i have broken down and finally bought myself a bench PSU. work suspended until further notice via digikey.....

thanks for the help.
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rjd2



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PostPosted: Tue Jan 20, 2009 9:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, i got my bench supply, so i can now troubleshoot much easier. hoping someone can help:


so on the bottom of the pcb, looking at the traces, the +15V line travels the length of the "bottom" of the board, with smaller traces branching off. -15V does the same thing on the "top" of the board. here's my problem:

the trace/branch that leads to pin 8 of two of the tl072's, and the lm311, turns to -12V at the very first pad. from then on, its -12V at each of the pin 8's. however, as far as i can tell, all the other places that long "bottom" +15V line runs to is still +15V. that first pad at which it turns to -12V is a 100nf ceramic cap. removed, i still get the same reading.

what could cause this? im baffled. the IC's are socketed, and with all of them removed, i still get the same readings. thanks for the help. im learning much from this.
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Rykhaard



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PostPosted: Tue Jan 20, 2009 9:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Now a possibility here is with how Ken has marked out the power input to the PCBs. I'm recalling this from his VCAs, which I recently corrected my own error on.
The power inputs are: (if memory serves me correctly)

+15, -15, GND, GND, +15

(I can go downstairs and get one to check)

My thought being, possibly your having the power input wires, hooked up incorrectly. Or possibly, the 10uF capacitors hooked up backwards, or to the wrong spots?

Could you take a high resolution photo of your PCB and post it here?
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Adam-V



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PostPosted: Wed Jan 21, 2009 2:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Pin 8 of the TL072s should be positive, not negative. Are you sure your supply is connected the right way around?

Cheers,
Adam-V

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rjd2



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PostPosted: Wed Jan 21, 2009 6:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Adam-V wrote:
Pin 8 of the TL072s should be positive, not negative. Are you sure your supply is connected the right way around?

Cheers,
Adam-V


hi adam, thanks for the help. im 1000% sure. ive gone over the pcb at least 4-5 times now, checked orientation of every IC and cap. pin 8 of the OTHER tl072 reads +15, with pin 1 -15V, so i think i have the power harness wired properly.

frustrated with my camera-this is the best i could get the shot. sorry, probably not helpful at all.


cgs vco 1.jpg
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cgs vco 1.jpg


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Adam-V



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PostPosted: Thu Jan 22, 2009 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's difficult to see on that photo but it looks like the notch on the end of the LM3900 is at the bottom which would mean it is in upside down. Can you just confirm which way up it really is?

Cheers,
Adam-V

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rjd2



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PostPosted: Thu Jan 22, 2009 7:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks adam-notch is definitely on top.

also, i meant that i see -15V at pin 4 of the other tl072, not pin 1. so, as far as i can tell, my harness wiring MUST be correct if i have ONE TL072 that is getting +15V at 8 and -15V at 4.

to be totally thorough, i compared this pcb to another stuffed cgs vco i have that is not built out, just stuffed. they are identical in parts, and orientation of parts. this other "bare" cgs vco reads the proper voltages for the IC's power pins.

outside of this modules issue, im just curious what could cause this symptom im seeing: +15 voltage rail that measures +15, +15,+15 as you follow the pins, and then BREAKS to go -12,-12,-12. everything after this one pin that SHOULD be +15 is -12. what could cause this?
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Adam-V



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PostPosted: Sat Jan 24, 2009 8:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Other than a short on the board or possibly a broken trace I can't think what would cause a different potential on the 15V rail. Perhaps someone else can offer some ideas on that?

Can you identify on the schematic which of the TL072s is the problematic one? By that I mean which part of the circuit it is - Linear FM and 1V/O input, CV1 and CV2 input or the Saw and Square output.

Cheers,
Adam-V

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rjd2



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PostPosted: Sun Jan 25, 2009 12:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Adam-V wrote:


Can you identify on the schematic which of the TL072s is the problematic one?
Adam-V


the 4 problematic IC's are the ones on the bottom in the pic i posted. in my pic, te TOP row of IC's, from L to R, is TL072, LM3900. these both have proper voltage at their power pins.

the bottom row, from L to R, is tl072, ca 3140 lm311, tl072. all 4 of these read -12V at pin 8, which all should(according to my records) be reading +15v.

directly above the BOTTOM LEFT MOST TL072 is the "zero 100k trimmer". its right-most leg is where the -12V starts, and runs that whole length along all of the pin 8's of that bottom row of IC's. maybe i should try removing that 100k trimmer?
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Adam-V



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PostPosted: Mon Jan 26, 2009 3:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm that defies all logic.

What voltages do you measure at the following points:

The top of the 100n capacitor on the right hand side of the zero trimmer
The top of the 150k resistor on the left hand side of the LM394
The top of the 100n capacitor on the right hand side of the top TL072

Cheers,
Adam-V

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rjd2



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PostPosted: Mon Jan 26, 2009 5:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks adam-if we are looking at the side of the pcb that shows all the components, not the trace side:

Adam-V wrote:
Hmmm that defies all logic.
The top of the 100n capacitor on the right hand side of the zero trimmer
-12V. BOTTOM READS -15V. THIS IS THE PIN AT WHICH +15V MAGICALLY TURNS TO -12V.
The top of the 150k resistor on the left hand side of the LM394
-13V.
The top of the 100n capacitor on the right hand side of the top TL072
+16V, IF YOU MEAN THE TL072 ON THE "TOP" OF SIDE OF THE BOARD.


does this help? to reiterate, removal of the 100n cap that is directly to the right of the zero trimmer does nothing. thanks for the troubleshooting tips.
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andrewF



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PostPosted: Tue Jan 27, 2009 3:06 am    Post subject: Reply with quote  Mark this post and the followings unread

interesting problem
note - the ca3140's V+ pin is pin7 not pin 8.

try this - remove the chips in sockets, one at a time. After removing a chip, check your voltages again (Don't do them all at once) if you find the voltages are as they should be, you have found the problem chip...or at least the area of concern.
Probably this won't help but its the easiest starting point as the chips are socketed. It is also possible the chips have been damaged by this point.

Just out of curiousity, monitor the -12V on one of the pin8s (where it should be +15V) and adjust the Zero trimmer.....does the voltage change a little?

Next, assuming voltages are still wrong with the chips out, remove the Zero trimmer and check voltages again.

Well - its a few things to try.
When things don't work you get to learn more Wink have fun
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rjd2



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PostPosted: Tue Jan 27, 2009 6:53 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks andrew. i already tried your steps 1 and 2. its not any of the chips; with all removed, it still reads -12V. tuning the zero trimmer has no effect on the voltage.

the only thing i havent tried yet is removing the zero trimmer. i'll try that today.
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rjd2



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PostPosted: Tue Jan 27, 2009 4:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, a new round of info.

so, just to double check my testing, i removed all 4 of the socketed IC's in the bottom row. that lead that was -12V(runs from pin 8 or 7 to all of them, supposed to be +15) now dropped to -3V. i then removed the zero trimmer, and it dropped to -.1V. removing the adjacent 100nf cap caused no change.

would it be feasible that i have a bridge to the - rail somewhere, and it could
cause this +15 leg to drop down to essentially 0? at this point, im doing this more for the learning process, although i sure would use the VCO if it gets fixed.
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Adam-V



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PostPosted: Thu Jan 29, 2009 4:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

It does sound like you have a short somewhere but I'm still surprised that you're measuring +15V and -12V on what is essentially the same PCB trace.

Did you perform the required modifications for whichever version board you have?

Try disconnecting the pots and removing the remaining ICs then measure again.

Cheers,
Adam-V

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Luka



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PostPosted: Thu Jan 29, 2009 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

i would suggest removing all the panel wires except what you need, which is just the waveform out wires (and just the saw out to start with). this makes the whole situation a little easier to handle and examine in detail
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rjd2



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PostPosted: Sat Jan 31, 2009 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

ok, a little more info(although im quite close to giving up on this particular module).

i removed all pots, all the IC's in question, and the zero trimmer and 100nf cap is still out.

that trace still reads 0V from that first pin all the way down. if i had ANY of the IC's, it doesnt matter which, it jumps up to -12V again. i might try this again and remove all the jacks as well, but im approaching my threshold of troubleshooting on this one....

thanks alot for all the advice, folks.
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Luka



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PostPosted: Sat Jan 31, 2009 8:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

some ideas from me
(not as experienced as the others, but i went through dramas with my cgs vco and solved them all)


good to focus on what is necessary
(which unfortunately is the main area where you have this + rail drop)

the core section is just the bottom chips
take out the lm3900 and top tl072 and dont let them interact with the core

perhaps you have a short under one of your sockets
i had that on a xoxbox i fixed for someone

you may have a bad pot also, disconnect your freq knob wires

check the connectivity between all the +15 rails connections with the chips out / chips in / combinations of chips in - out


....
good tip

print out a copy of the pcb layout and schem and mark down everything you check with a texta so you can work out what you have checked and what you havent (saves double handling)

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