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TZFM SAW VCO
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sduck



Joined: Dec 16, 2007
Posts: 453
Location: Nashville
Audio files: 5

PostPosted: Mon Aug 27, 2012 6:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

So I replaced both of the diodes in the B206-B206 spots. They were fine when I installed them. Turned it on, checked all the voltages, everything is fine. Turned off power, installed the CA3280. For about a minute after powering up the unit it seemed fine, but then the CA3280 started getting hot about a minute into it. When powering off it seems the diode in B205 has blown - it's now a wire.

So what the hell is going on? Do I need a higher value zener? I used mouser 512-1N5223B, which is a 2.7v 500mW zener. Anyone have a recommendation for a bigass zener that won't blow out?

And thanks Dave for monitoring this and being helpful - I may just switch the thing over to your conversion method - it might be easier and faster.
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davebr



Joined: Jun 09, 2007
Posts: 194
Location: portland, or

PostPosted: Mon Aug 27, 2012 10:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

sduck wrote:
So I replaced both of the diodes in the B206-B206 spots. They were fine when I installed them. Turned it on, checked all the voltages, everything is fine. Turned off power, installed the CA3280. For about a minute after powering up the unit it seemed fine, but then the CA3280 started getting hot about a minute into it. When powering off it seems the diode in B205 has blown - it's now a wire.

So what the hell is going on? Do I need a higher value zener? I used mouser 512-1N5223B, which is a 2.7v 500mW zener. Anyone have a recommendation for a bigass zener that won't blow out?

And thanks Dave for monitoring this and being helpful - I may just switch the thing over to your conversion method - it might be easier and faster.

Normal current draw is less than 100mA and you are dropping 3V so you are at 300 mW which should be fine if everything is working correctly. However the current is probably much higher to heat up the chip and that is taking out your zeners. I would just put in wire for now until you can get the current draw under control.

The easiest way to blow up an OTA is to source too much current into the Iabc pin. Section B is sourced from a resistor so that should be fine if the resistor value is correct.

I would assume your OTA is toast by now, but you might still be able to use it to debug. I would put it in with both pin 3 and 6 lifted. See if the heat issue goes away. If so, then I would use your multimeter to measure the current between the lifted pin and the socket. There are no pin numbers on the schematic so I'll assume section A is pin 3. I would start with pin 6 first. If the current is <2mA then I would bend that pin back and into the socket. My guess is your current for pin 3 will be way too high. That is controlled by the expo converter and it could be shorted. There is a 6K8 resistor in series which should prevent more than 2 mA with a voltage drop of 13.6 volts. The Iabc pin is one diode drop above the negative rail, so if the collector of the expo converter goes above ground it could damage the part. You could connect the end of the 6K8 resistor to the negative rail with pin 3 lifed and monitor the voltage on the emitter of the expo converter as you adjust the frequency over the range.

I would verify all the voltages on the OTA socket as well to make sure something else isn't haywire.

Sometimes when I'm debugging a system like this, I will bypass the expo converter with a simple trim pot and the right series resistor to ground. This should give you some frequency control. Likewise you can connect the series resistor from the expo converter to either the negative rail or a diode drop above it and monitor the voltage. It allows you to divide the circuit into two halves that are independent for debug. You also have two sections to deal with. Isolate it to a section, and then to what is causing the excessive current.

Just a thought.

Dave
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sduck



Joined: Dec 16, 2007
Posts: 453
Location: Nashville
Audio files: 5

PostPosted: Wed Aug 29, 2012 7:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Dave.

This is taking me too long, as I've had visitors and zero time to actually deal with the thing.

Today I pulled the ca3280, and replaced the B205 diode just so things would be correct so I could check voltages. While checking something, I don't know what, the other diode blew out again - the one in the B206 location. Probably just an accidental contact made where one shouldn't have been made, unrelated to the other problem. This is getting very frustrating.

I went over the thing with a magnifying glass today, no solder shorts, cold solder, missing solders, etc. Also checked resistor values - everything's correct. As I mentioned earlier, I was particularly meticulous about getting the parts right on this build after the stupid part problems I had on the last one.

Could a fake/blown CA3280 be whats causing all this excess current to be drawn? I have another CA3280 here, but don't want to sacrifice it until I know it won't overheat and/or blow out immediately.

Oh, and which is the expo converter you speak of? I don't have such a thing on my layout. Probably a dumb question, please bear with me on this.
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sduck



Joined: Dec 16, 2007
Posts: 453
Location: Nashville
Audio files: 5

PostPosted: Sat Sep 01, 2012 8:55 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok, a follow up report. Dave and I switched to email - he very generously offered to help me sort through this, and I was all ears. And scope and DMM probes. Anyway, after testing everything to determine if there was a short, wrong parts, or whatever else that could be wrong in my build, Dave was able to deduce that most likely it was a flaky CA3280. So I threw in another one I had here, and it works! Everything is hunky dory - I've got reversing waveforms, everything. Now to calibrate...

I've thanked him profusely via email, but I want to make sure that Dave gets a public thanking also - it's marvelous that he's able to spend time helping others debug stuff like this! Thank you!
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neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Tue Feb 25, 2014 12:54 am    Post subject: Reply with quote  Mark this post and the followings unread

I've been having a problem with one of my two Teezers. When oscillating at negative frequencies the sine doesn't work, the triangle is a positively offset saw and the saw is negatively offset.

The output of A2 was swinging as it should. A4 seemed to be working when I measured it so I kept looking. I noticed that when turning the initial frequency into the negative I couldn't get D12 and D13 to forward/reverse bias correctly.

When measuring I accidentally touched D11 with my multimeter probe and it started working! I sweep the initial frequency up into the positive again: all good. Then I turn it back to negative: not working. Touch anywhere on the A4b-6 junction with a metal object and it kicks in again. Turn it to positive then back to negative and it stops once again.

I reheated all the solder joints in that area and made sure I had good continuity. I swapped A4 with two other OPA2134s, one of which was happily working as A4 in my other Teezer. Still the same deal. I try a TL072 and it works!

Any idea why my Teezer is rejecting OPA2134s?

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frijitz



Joined: May 04, 2007
Posts: 1725
Location: NM USA
Audio files: 54

PostPosted: Tue Feb 25, 2014 12:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Andrew --

Sorry about your trouble. A4b-6 is grounded, so touching there shouldn't have any effect. scratch

If A2's output is correct, then the trouble must be around A4. Please carefully check all the component values and connections.

Ian


neandrewthal wrote:
I've been having a problem with one of my two Teezers. When oscillating at negative frequencies the sine doesn't work, the triangle is a positively offset saw and the saw is negatively offset.

The output of A2 was swinging as it should. A4 seemed to be working when I measured it so I kept looking. I noticed that when turning the initial frequency into the negative I couldn't get D12 and D13 to forward/reverse bias correctly.

When measuring I accidentally touched D11 with my multimeter probe and it started working! I sweep the initial frequency up into the positive again: all good. Then I turn it back to negative: not working. Touch anywhere on the A4b-6 junction with a metal object and it kicks in again. Turn it to positive then back to negative and it stops once again.

I reheated all the solder joints in that area and made sure I had good continuity. I swapped A4 with two other OPA2134s, one of which was happily working as A4 in my other Teezer. Still the same deal. I try a TL072 and it works!

Any idea why my Teezer is rejecting OPA2134s?
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neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Tue Feb 25, 2014 5:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

I thought I had verified all the voltages on a previous occasion, but the B206 zener was shorted causing the power for A4 to be asymmetrical. Can't believe I didn't check that sooner. I guess the TL072 was just not as picky with it's supply voltages because it's not as fancy. Now it works with the OPA!

frijitz wrote:
A4b-6 is grounded, so touching there shouldn't have any effect. scratch


Oops, I meant pin 5 doh

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frijitz



Joined: May 04, 2007
Posts: 1725
Location: NM USA
Audio files: 54

PostPosted: Tue Feb 25, 2014 6:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

neandrewthal wrote:
I thought I had verified all the voltages on a previous occasion, but the B206 zener was shorted causing the power for A4 to be asymmetrical. Can't believe I didn't check that sooner. I guess the TL072 was just not as picky with it's supply voltages because it's not as fancy. Now it works with the OPA!

D206? That'd do it. Don't know why one opamp worked and not the other, though. I hope you are enjoying the two modules. I may not have mentioned it here, but there are now videos at my utube page illustrating some of the possibilities of using a pair together.

Ian
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neandrewthal



Joined: May 11, 2007
Posts: 672
Location: Canada

PostPosted: Wed Feb 26, 2014 3:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm definitely enjoying them and have been for years even in crippled form. I also liked your videos a lot when I ran across them. Now that you mention it I'm gonna go watch them again.
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thorncore



Joined: May 03, 2013
Posts: 8
Location: uk

PostPosted: Mon Jan 19, 2015 10:12 am    Post subject: Reply with quote  Mark this post and the followings unread

hi,
I have recently finished stuffing a Teezer
I have verified correct voltages at all of the test points mentioned earlier in the thread.

They are all correct apart from the 7v section relating to the supply to the LM311s.

I get a voltage reading of about +9v
at U2-8 , U3-8

and around -9v
at U2-1/4 ,U3-1/4

any ideas about the possible cause?

Thanks Smile
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frijitz



Joined: May 04, 2007
Posts: 1725
Location: NM USA
Audio files: 54

PostPosted: Mon Jan 19, 2015 1:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
hi,
I have recently finished stuffing a Teezer
I have verified correct voltages at all of the test points mentioned earlier in the thread.

They are all correct apart from the 7v section relating to the supply to the LM311s.

I get a voltage reading of about +9v
at U2-8 , U3-8

and around -9v
at U2-1/4 ,U3-1/4

any ideas about the possible cause?

Thanks Smile

Are you powering from +/- 12 V?
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thorncore



Joined: May 03, 2013
Posts: 8
Location: uk

PostPosted: Mon Jan 19, 2015 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

hi there,

Yes it is a 12V build.
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frijitz



Joined: May 04, 2007
Posts: 1725
Location: NM USA
Audio files: 54

PostPosted: Mon Jan 19, 2015 3:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
hi there,

Yes it is a 12V build.

Hmmm... Only thing I can think is the the zener voltage is wrong. Needs to be 5.1V.
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thorncore



Joined: May 03, 2013
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Location: uk

PostPosted: Mon Jan 19, 2015 3:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks,
I will double check everything tomorrow.
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thorncore



Joined: May 03, 2013
Posts: 8
Location: uk

PostPosted: Mon Jan 19, 2015 4:20 pm    Post subject: Reply with quote  Mark this post and the followings unread

managed to get one last squint out of my tired eyes...

the Zeners are the correct value; 1N5231B
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frijitz



Joined: May 04, 2007
Posts: 1725
Location: NM USA
Audio files: 54

PostPosted: Mon Jan 19, 2015 6:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
managed to get one last squint out of my tired eyes...
the Zeners are the correct value; 1N5231B

Thank you. Yeah those tiny numbers are really hard to read.

I assume you are using the Bridechamber board? And that there are no oscillations at all?

This is a real head-scratcher. Could you please recheck that the diodes in question are D203/4 located to the left of U2, and that they are oriented correctly?

Also that the caps C211/2 are oriented properly?

Please also double check that there are no solder bridges in the ground-plane region under U2/U3. Were there any difficulties soldering to the ground points in that region (the ones with the thermal relief pattern)?

I double-checked via data sheets that the chips U2/U3 draw plenty of current to switch the zeners. The only way there could be such a small current through the diodes would be if the chips weren't powered.
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thorncore



Joined: May 03, 2013
Posts: 8
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PostPosted: Tue Jan 20, 2015 3:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Yes the Bridechamber board ,
diode orientation and value at D203/4 are correct .
caps C111/2 are correct,
I had no issues with soldering and no shorts are visible.

the U2/U3 measurements I took were before putting in any ICs or testing for output
just to check correct voltages.

I can't test with ICs until tomorrow unfortunately
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frijitz



Joined: May 04, 2007
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PostPosted: Tue Jan 20, 2015 4:45 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
the U2/U3 measurements I took were before putting in any ICs or testing for output just to check correct voltages.

Well, there's your trouble. The zeners are in series with the ps lines, so you won't see the correct voltages without the chips inserted.
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thorncore



Joined: May 03, 2013
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Location: uk

PostPosted: Tue Jan 20, 2015 4:51 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ah thank you sir,I suspected that might be the case

Fingers crossed everything is ship-shape tomorrow and I can press on with Teezer 2 and then a Threeler.
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frijitz



Joined: May 04, 2007
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PostPosted: Tue Jan 20, 2015 6:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
Fingers crossed everything is ship-shape tomorrow and I can press on with Teezer 2 and then a Threeler.

Sounds like you are being careful with the build, so hopefully there won't be any major problems. This is a fairly challenging project, so pleas let us know how it goes.

Ian
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thorncore



Joined: May 03, 2013
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PostPosted: Wed Jan 21, 2015 4:52 am    Post subject: Reply with quote  Mark this post and the followings unread

I certainly was being very careful with the build,the Teezer is by far my most in depth project so far and I really wanted to minimize the potential pitfalls.

I have learned a heck of a lot making the right component choices and grasping the design (ish)

Anyway it paid off and preliminary tests indicate a successful build Very Happy

I am getting wonderfully deep TZFM and a great range of frequency.

Very excited to put it through its paces and introduce it to its sister.

Thanks for your help and great designs Very Happy
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emmaker



Joined: Aug 10, 2007
Posts: 11
Location: Portland, OR

PostPosted: Thu Jan 22, 2015 3:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm building up some of my backlog and working on a +/- 15V Teezer using the Bridechamber parts kit. I'm going to use the zener substitutes to get it to work with 15 volts too.

The quantities in the kit for some of the resistors is off, some missing and some values not on the BOM are in the kit. Also out of the stock 6 zeners, 2 are correct, there are 2 6.X volt ones and 2 are missing. Got a 33pf cap too which I can't find in the BOM.

I checked this thread for any value changes/tweaks and really didn't see anything major. So my question is the BOM from Bridechamber correct and can I build it from that?

Thanks much.
Jay S.
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frijitz



Joined: May 04, 2007
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PostPosted: Thu Jan 22, 2015 5:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

thorncore wrote:
Anyway it paid off and preliminary tests indicate a successful build Very Happy

Wonderful! Really glad to hear that.

Ian
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frijitz



Joined: May 04, 2007
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PostPosted: Thu Jan 22, 2015 6:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

emmaker wrote:
...The quantities in the kit for some of the resistors is off, some missing and some values not on the BOM are in the kit...

So far as I know Scott is sending out current docs, which should have the correct BOM. I suggest you contact him about your discrepancies. Or let me know which parts you need and I'll be happy to send them to you.

Ian
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emmaker



Joined: Aug 10, 2007
Posts: 11
Location: Portland, OR

PostPosted: Thu Jan 22, 2015 6:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Ian.

I'll check with Scott. Sometimes he's slow on getting back so I thought I'd try here first.

Also thanks for the offer of parts. I have most of the parts already and what I don't have I'll put in a Mouser order I have going out next week. It'll be a lot easier for everyone that way.

Thanks again.
Jay S.
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