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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.
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