MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

TM3030 VCO Problem
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author TM3030 VCO Problem
letness
After many months, I'm finally getting around to building my TM3030. The MIDI works, but I'm only getting slight clicks sound-wise (so the VCA is working, too, I guess).

After reading up on similar issues here on Muffs, I tested the waveform switch, and it seems to be working, and reflowed everything around the VCO. I also swapped Q1 (a suspect 2SK30A-O) for Q2 (a J201 from a reliable source). I'm beginning to wonder whether my 182Ls and 212L, which are correctly marked, are the problem. Any chance these are fake/mis-marked? Seems a stretch, but maybe I'm wrong.

Also, I'm using this for C9--it "fits" (diagonally), but maybe it's not the right choice?: http://www.mouser.com/Search/ProductDetail.aspx?R=FKP2C021001G00ESSDvi rtualkey50520000virtualkey505-FKP20.01%2f63%2f1

Any advice welcome!
Synthbuilder
That cap should work so I guess the problem will be elsewhere.

I don't think the BC182L and BC212L would be fake. They are a common part and sell for pennies so I don't think faking them would be profitable. That said, they seem to fake anything these days - we just had a case of fake TL072s. I would always recommend, if possible, that all parts are bought from well known suppliers like Farnell, Mouser, Digikey and the like.

What are the voltages on pin 2, pin 12, pin 13 and pin 14 of U6?

Do you have access to a scope?

Tony
letness
Thanks for the speedy reply, Tony.

On U6, I get the following:

Pin 2: 5.33V
Pin 12: 0V
Pin 13: 0V
Pin 14: 0V

I do have a cheap digital scope, but I'm not sure what to probe.

I've also attached a photo, just in case I've overlooked something obvious.

Thanks again!

[/img]
Synthbuilder
letness wrote:

On U6, I get the following:

Pin 2: 5.33V
Pin 12: 0V
Pin 13: 0V
Pin 14: 0V


You sure about those? 13 and 14 should be 5.33V and 12 should be 4.6V or so. Check it again but if it's still reading the same then check the soldering under U6 around pins 11 to 14. If that's OK then pull out U6 and check the pins didn't get folded underneath the chip - although it looks OK in the photo.

If the voltages are good then with your scope check the top and bottom pins of the waveform switch. You should see the sawtooth and square waves there if the VCO is working.

Tony
letness
Okay, I've got the correct voltages out of pins 2 and 12-14 of U6, but I don't see anything of note on the scope. Is there something else I should check? Thanks again.
Synthbuilder
The VCO is not oscillating then. So it'll be worth checking all the components again - particularly D2, R6 and R9. Then if all is well then I'd replace the BC212L and BC182L transistors first. Transistors are pretty rugged but I did have a TM3030 here not so long ago with a duff BC182L or BC212L that may have been damaged by too much heat or static. And maybe there are fake devices out there? If that doesn't work replace the THAT300.

Tony
Synthbuilder
Actually, there is another possibility but I'm not so sure it is this since the voltages around the THAT300 now seem OK.

What's the voltage at pin 7 of U7? This should change depending on the note you play and will be from 1V to around 5V. However, if it's stuck very high, like 10V, it might stop the VCO from oscillating.

Tony
letness
Thank you for the guidance Tony. I'll try all of your suggestions and post the results once I get out from behind a pile of work. Again, really appreciate the help.
letness
Did as you suggested and tested D2, R6, R9, and pin 7 of U7--all good. Then replaced the 182Ls and the 212L and it came to life. I suspect the 212 was the problem, but as I replaced all three at the same time, I can't be sure.

In any event, my TM3030 sounds fantastic! Thanks so much for your help!
Synthbuilder
thumbs up
studyman
i saw in this picture below that there are some holes whithout soldering like near U8 or D8, behind the decay pot....is that normal ? do we have to leave this holes empty ?
Thanks
Pierre
Synthbuilder
studyman wrote:
i saw in this picture below that there are some holes whithout soldering like near U8 or D8, behind the decay pot....is that normal ? do we have to leave this holes empty ?


Those are vias. They allow copper tracks on the top side to connect with tracks on the bottom. You do not need to fill these with solder. I normally do, however, since I remember the old days when vias were a weak point in board manufacture. That is not the case these days and they can be left unsoldered.

Tony
letness
Hate to say it, but I've got another issue. When I power up the TM3030, the pitch is stable. After a few minutes, the pitch starts to wobble--it sounds, for lack of a better phrase, like the vco is seasick. Then the pitch jumps up several octaves and is stable again--rock-solid stable. But the range is way up toward the upper end of my hearing range. Sometimes (but only sometimes), it gradually drifts back down to the expected range.

I'm using the recommended EH power adaptor, so I don't think that's the issue. I've rewired the power connections (including the switch), re-flowed everything I could see that might be affecting the power, and made sure that the case (which is metal) is properly grounded (i.e., I wired the 0v to the case, which shouldn't be necessary, as I grounded the circuit via the MIDI socket). The problem persists.

This problem began, I think, when I used a drum machine connected, via MIDI, to the TM when the TM's power was off. For some reason, the TM's LEDs lighted up, despite the fact that its power was off. Have I fried something? If so, what should I check/replace?

My apologies for not being better at trouble-shooting. I have much to learn, and am trying, as a long-confirmed non-engineer, to learn what I can. Any tips greatly appreciated!
Synthbuilder
letness wrote:
When I power up the TM3030, the pitch is stable. After a few minutes, the pitch starts to wobble--it sounds, for lack of a better phrase, like the vco is seasick. Then the pitch jumps up several octaves and is stable again--rock-solid stable.


Probably a cold solder joint or intermittent connection somewhere. They can be very difficult to track down. Try pushing gently down on the board when it's on and playing and listening to the output. Support the rear of the board is you're only using the pot brackets. The idea is that slightly flexing the board will reveal the weak points. If it's only the VCO pitch that is misbehaving then the problem is possibly around the glide and CV control - circuitry around U4, U5, U7 & U7.

If you have IC sockets then take each IC out and push it back in again. Dirty IC socket contacts and/or IC pins can show this sort of behaviour.

Tony
letness
Great! Makes perfect sense that this happened after I installed the pcb in an enclosure (which involved some epoxy and maybe some bending of the board--we'll see). Will do as you suggest. Thanks again Tony--really appreciate the help.
letness
Problem fixed Tony. Many thanks. I'm now working on getting that hollow sound from the square wave--it sounds very good at the moment, but not quite up to the demos on your page (in particular, the third unprocessed demo). Again, I really appreciate the help.
Leverkusen
deleted for being a bit stupid with counting... d'oh!
Leverkusen
It seems that I can't get the VCO section get to work. All voltages suggested to check are as they should be and D2, R6 and R9 are alright too. I already exchanged Q2, Q3, Q4 and Q5 and swapped both THAT300 against each other with no effect.

I only get the filter sweep sound with frequency, resonance, depth, decay, accent and volume working as expected. All LED's are nicely blinking and slide seems to be working too.

I built it with the BA662 clone from open music labs and a second J201 instead of the 2SK30A-O. 2SC945 and 2SA733 were used instead of BC182 and BC212, no 2SC1583 but two BC449. I power it with 20 V DC from a lab PSU.

The only thing I am not sure about is that I had to use a 2 -5 % polyester film cap at C9 cause the high quality polystyrene was the only part missing to complete the build and I did not expect it to be crucial and though I could replace it later on when it will not sound nice, was I wrong here?

Any suggestions would be highly appreciated.
Synthbuilder
Leverkusen wrote:
It seems that I can't get the VCO section get to work.


It may be worth checking those Japanese transistors in the VCO. Do you have a transistor or component tester?

The original 303 used a polyester capacitor - I've just used a polystyrene as you get slightly better tuning stability with temperature changes.

Tony
Leverkusen
Synthbuilder wrote:
Leverkusen wrote:
It seems that I can't get the VCO section get to work.


It may be worth checking those Japanese transistors in the VCO. Do you have a transistor or component tester?

The original 303 used a polyester capacitor - I've just used a polystyrene as you get slightly better tuning stability with temperature changes.

Tony


The VCO, or the part that is actually oscillating is the SCR, isn't it ( I have a vague idea of what the exp. converter and the FET buffer are doing but don't understand where and why the oscillation comes from and how it gets to the buffer)? So I assume you mean the 2SC945 and 2SA733?
I did not find the BC182 and BC212 so I got these from Banzai instead. I ordered them in doubles so the ones I swapped came from the same bag. Could be that they are all broken then.

Unfortunately I don't have a transistor tester - is it possible to do with a multimeter? Or could I just build something with a battery and a LED?
Synthbuilder
Yes, I was thinking about those Japanese parts and making sure the pin out is what it should be. It's not trivial to do with a meter so a tester is a worthwhile purchase. This sort of thing is great:

http://www.ebay.co.uk/itm/Digital-Combo-Component-Tester-Transistor-Di ode-Inductor-LCR-Capacitor-ESR-Meter/252465614412

The expo discharges the timing capacitor (C9) at a rate determined by the voltage across pins 2 and 3 of U6. When the voltage across C9 falls to around 5V the SCR rapidly turns on and pulls the voltage across the timing capacitor to a little less than +12V. The base emitter current through the top transistor (Q3) is now not sufficiently high to keep the SCR on so the voltage across falls again and the process repeats. Q5 acts as a diode to roughly temperature compensate the base-emitter voltage drop of Q4.

Tony
Leverkusen
Synthbuilder wrote:
Yes, I was thinking about those Japanese parts and making sure the pin out is what it should be. It's not trivial to do with a meter so a tester is a worthwhile purchase. This sort of thing is great:

http://www.ebay.co.uk/itm/Digital-Combo-Component-Tester-Transistor-Di ode-Inductor-LCR-Capacitor-ESR-Meter/252465614412

The expo discharges the timing capacitor (C9) at a rate determined by the voltage across pins 2 and 3 of U6. When the voltage across C9 falls to around 5V the SCR rapidly turns on and pulls the voltage across the timing capacitor to a little less than +12V. The base emitter current through the top transistor (Q3) is now not sufficiently high to keep the SCR on so the voltage across falls again and the process repeats. Q5 acts as a diode to roughly temperature compensate the base-emitter voltage drop of Q4.

Tony


Thank you Tony for the explanation, I am hoping to get some more insight in what is actually happening in those circuits!

Meanwhile I found a step by step guide to check transistors by doing multiple diode tests on different leg combinations with a multimeter. It seems as if the SA945 I desoldered for exchange are not working and I found some 182L/212L at ebay but I will also look for a tester, they seem to be not that expensive - thanks for the tip.
Leverkusen
I had the new transistors in the postbox today and and swapping the 2SC945 and 2SA733 against BC182L and BC212L solved the problem.

It is running now!

Thank you again Tony for the support and the design!

spinning
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Page 1 of 1
Powered by phpBB © phpBB Group