TM3030 issue - sound cuts out after a bit

[tvh]

This one is a weird one since if I didn't know this TM3030 better I might think it's fine - I recently finished a midiphy seqv4+ and the first synth I hooked up was the TM3030. It was banging at first.

Then, tonight the sound cuts out - not really cut out but sounds like the resonance is cut in half. Before, I could close the filter, crank the resonance, decay and amount and get some great ripping chirps. When I turn it off, wait a bit, it seemed ok for a few seconds. But now it's exhibiting the same behavior regardless of a reset or not. It's like a basic monosynth now.

It's still getting gate signal via midi so it's probably not the PIC and I think the firmware doesn't control the resonance anyway, and the volume is working fine. It's like the resonance is only half (or less) what it should be. Any thoughts?

[Synthbuilder]

There's probably a bad connection somewhere on the board. Open it up and send it some midi. Gently push down on the board in various places across the board and see if it springs to life. It's quite possibly the section around THAT300 chip in the middle of the board. Once you've found the spot then check the soldering around that point. It may even be the IC socket for the THAT300.

Tony

[tvh]

Ok thanks Tony I'll give that a shot.

[tvh]

No luck. I tried pressing everywhere and wiggling all the components. I don't hear any difference or see any loose connections.

It's like it's missing the classic squeal and I only hear it a little on accent notes. It used to be very pronounced. Could it be component failure somewhere? I usually drive the volume at max if that makes a difference.

[Synthbuilder]

Could it be component failure somewhere?

It could be. It was the intermittency that made me think it was connection fault somewhere. But if it's always doing it now, then that could be a component fault.

Lack of resonance means that either the gain of the filter has decreased or that the gain within the resonance feedback loop has decreased. The power supply does have a knock on effect on the filter gain, so maybe check that first. Make sure the 5V3 pad is truly 5.33V.

Q29 or Q26 going bad would also stop the resonance from working properly.

Just to check it's not modulation wheel data being sent incorrectly from your sequencer it may be a good idea to play the TM3030 manually from a keyboard and see if that changes things. Mod wheel data will activate the filter cut-off control and can have some odd effects.

Tony

[tvh]

Thank you for the assistance on this. Sadly, no luck. Getting 5.3V. I replaced Q26 and Q29 with new 550s and same as before. I did mess with the modwheel with my keystep hooked up and that is behaving as expected. A cool feature that I never really used much, will have to explore it further on the sequencer when I get this back up and running correctly. Still very little resonance except on accent, which lasts extremely short (as it should I believe). I'm wondering if there's anything else I can try?

[Synthbuilder]

Still very little resonance except on accent...

That's interesting. Resonance should not be affected by accent at all. Although the resonance control does affect the amount the filter opens by raising the cut-off frequency when an accent is received.

Unfortunately, I don't have any other specific suggestions to make other than perhaps the resonance pot itself is not working correctly.

Do have any recordings of it misbehaving?

Tony

[tvh]

Maybe it was just the added volume with the accent bringing out the resonance more. I'll see if I can make a recording at some point.

Thanks -Tom

[tvh]

Actually question on the Freq pot - I notice when I measure the two outer pins I only get 25K, whereas on the resonance I measure 50K. I replaced the Freq pot thinking maybe something was off with it but the new one is measuring 25K also. Is that by design? I know there's CC control over the freq pot so figure there's more going on there than just the pot itself.

Thanks

[Synthbuilder]

I notice when I measure the two outer pins I only get 25K, whereas on the resonance I measure 50K.

Did you measure the pot with it still in the board? If so, the resistance reading doesn't tell you much about the pot as there is a lot of other stuff connected to the pot. The frequency pot will have different components connected compared to the resonant pot which will affect the resistances you see. Unfortunately, the only way to measure a pot's resistance is to take it out of the board. That said, measuring resistances in situ can help sometimes, particularly if you are looking for a short circuit.

It's much better to look at the signal on the wiper of the pot with a scope as you move the pot. However, the unit has to be powered up which can make taking the measurement difficult.

[tvh]

I did measure it in place. I figured it wouldn't have been that simple, that would have been too easy.

I'm planning on picking up one of the new TD-3's anyway since I want to try having a double 303 sound so I'll just relegate this to the more bass-heavy parts since the squeal is mostly gone when you open the filter. Still sounds incredible through my metal-end distortion pedal, though so it's not like it's a lost cause at least.

[Paradigm X]

dont give up mate! did you try replacing the resonance pot like tony suggested? Ive had to replace the resonance pot on one tm3030 and two x0xb0xes so it could be the culprit.

The tm3030 sounds far better than the behrginer to my ears (better than the x0x too).

[tvh]

Interesting, I didn't think the pots wear out so much. From using it so much? Or the dual gang nature you think just more prone to defects?

I don't have a spare pot for this one, but I'll be sure to grab an extra (or two) next time I send Mouser some money.

[Paradigm X]

i dont know tbh, out of my knowledge. ive also replaced 3 volume pots on 2x x0x and the oakley. maybe its the oiriginal design? seems a big coincidence otherwise. but i dont know enough to be able to comment with confidence

for clarity the tm3030 resonance pot i replaced was from a second hand one a mate bought so no idea how much abuse theyd received. the two x0xen were both mine and they did get a lot of use. as youd expect from a 303!

[tvh]

Quick update on this - I did just replace the resonance pot and it seemed to make a difference. Sounds even better now! Thanks for the suggestion Tony and Paradigm

Tomorrow I'm getting a TD-3 so I'm looking forward to comparing them regardless.

[Paradigm X]

i shouldnt have posted that. just noticed my resonance pot is going scratchy now too might try cleaning it first if that fails, replace the pot.

[tvh]

Latest update - I did replace the pot, at first it was fixed (and I posted my excitement here) but then quickly turned to crap. It would cut in and out depending on how hard I cranked the resonance pot, and to me that signaled there was something making momentary on/off contact somewhere. I had some time this morning and reflowed the resonance pads on the PCB one at a time and apparently that did the trick. Anyways back to normal now. Must have been a poor joint from the beginning and just moving it as much as I have been dislodged it enough to bring the issue out. Not 100% sure but I'll take it where I can get it at this point.