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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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 Posted: Sat Jun 23, 2012 7:15 am Post subject:
VCO issue |
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Hello, I'm having strange behaviour from an oscillator I've built recently. The sawtooth waveform is small and the shape is not quite right, also when turning the Frequency, the wave disappears from around 5 down to 0. I've read a similar post to this behaviour but there was no real conclusion. This is my 5th and final oscillator, the other 4 work great I just can't see what the issue is with this one. I've compared this to the working oscillators as much as I can and I've swapped the chips to a working oscillator and they work fine. I've also replaced J112 which made no difference. So to me this says it's the board somewhere. It won't be the first time I've missed something so here's some pics...
Any help will be much appreciated...
Thanks, Phil.
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yusynth
Joined: Nov 24, 2005
Posts: 1214
Location: France
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| Posted: Sat Jun 23, 2012 11:08 am Post subject:
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Some of the solders don't look very neat : dull grey , no shine. What type of solder did you use ?
Also, check with a magnifying glass for micro-breaks or micro-bridges.
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Yves |
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yusynth
Joined: Nov 24, 2005
Posts: 1214
Location: France
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| Posted: Sat Jun 23, 2012 11:15 am Post subject:
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Can you check the orientation of the diode on the top left of the first photo, it is hidden by the capacitor. Normally the ring is on the right ?
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Yves |
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yusynth
Joined: Nov 24, 2005
Posts: 1214
Location: France
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| Posted: Sat Jun 23, 2012 11:24 am Post subject:
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Can you also verify that you have the right values for R15 and R14 and check that you did not swap them (it's hard to say on the photo if the ring is red or orange, but i have the feeling that they are swapped)
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Yves |
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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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| Posted: Sun Jun 24, 2012 10:38 am Post subject:
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| yusynth wrote: | Some of the solders don't look very neat : dull grey , no shine. What type of solder did you use ?
Also, check with a magnifying glass for micro-breaks or micro-bridges. |
Solder was just some lead free stuff from a local shop, it didn't seem the best when using it but I'd ran out of my usual brand. I'll got through all the joints with a multimeter for continuity and go through with my magnifying glass again. |
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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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| Posted: Sun Jun 24, 2012 10:39 am Post subject:
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| yusynth wrote: | | Can you check the orientation of the diode on the top left of the first photo, it is hidden by the capacitor. Normally the ring is on the right ? |
Yes ring is on the right... |
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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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| Posted: Sun Jun 24, 2012 10:41 am Post subject:
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| yusynth wrote: | | Can you also verify that you have the right values for R15 and R14 and check that you did not swap them (it's hard to say on the photo if the ring is red or orange, but i have the feeling that they are swapped) |
R14 and R15 are both 100K. I'm using an SSM2210 so have changed R15 from 10K to 100K as per your instructions. I've done this on my other 4 oscillators and they work well... |
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yusynth
Joined: Nov 24, 2005
Posts: 1214
Location: France
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| Posted: Sun Jun 24, 2012 11:46 am Post subject:
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OK for R14 and R15 and the diode. Have you got an oscilloscope ?
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Yves |
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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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| Posted: Sun Jun 24, 2012 12:35 pm Post subject:
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| yusynth wrote: | | OK for R14 and R15 and the diode. Have you got an oscilloscope ? |
Yes, I can take some pictures at different points for you... |
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yusynth
Joined: Nov 24, 2005
Posts: 1214
Location: France
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| Posted: Sun Jun 24, 2012 12:44 pm Post subject:
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OK, you could take picture of the sawtooth signal on pin 5 of U6 at 100 Hz, 1kHz and 5kHz (roughly), indicate the v/square and ms/square that you use.
A good idea is to look for the same signals on a working VCO to compare.
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Yves |
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djfill
Joined: Jan 10, 2012
Posts: 26
Location: Cardiff, Wales, UK
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| Posted: Mon Jun 25, 2012 2:52 pm Post subject:
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| yusynth wrote: | OK, you could take picture of the sawtooth signal on pin 5 of U6 at 100 Hz, 1kHz and 5kHz (roughly), indicate the v/square and ms/square that you use.
A good idea is to look for the same signals on a working VCO to compare. |
Hi Yves, here's the information you asked for...
So what happens is I either get nothing or approx 10kHz. This happens when I turn the freq passed 5 (0-5 get nothing, 5-10 get 10kHz). The wave (when visible) does look good, better in fact than a working oscillator, but freq control does nothing and the Saw output looks an odd shape.
| Description: |
| Bad oscillator. Pin 5 @10kHz (the only frequency it will produce) Time= 5 micro Seconds per division V=2V per division |
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1.04 MB |
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73 Time(s) |
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| Description: |
| Saw output (same freq and oscilloscope settings) |
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1.12 MB |
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71 Time(s) |
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