Sequential Drumtraks tuning problem

[cutoffres]

Hi!
Got a Sequential circuits Drumtraks drum machine, the main problem is that VOLUME and TUNING individual sounds do not works on all sounds.
I have replaced a few ic U101; U226; U216; U217; U216; U214 and the fault is still there.

I've also the feeling that the METRONOME is missing beats maybe it is related or not to the individual TUNING and VOLUME problem?

Concerning VOLUME and TUNING i would like to understand how it works in order to to troubleshoot it. The main part that i don't understand is how the individual TUNING and VOLUME is activated when a sound switches is pressed? Which ic or component does that job?
Thanks for the help.
The service manual: https://www.polynominal.com/site/studio ... manual.pdf

[crochambeau]

Page 6, bottom paragraph gives a synopsis of the per voice tuning.
Page 14, right hand side shows bank of 556 ICs that serve as tuning clocks.

I would guess that poking around those areas and comparing functional channels to reluctant channels may be the ticket. I have not messed with this though, as last I checked my Drumtraks still does the per voice tuning (hold MIDI note and apply pitch bend before release to define pitch of *next* instance of same note)

With respect to volume, it appears that is handled at the voice DAC (6070). Example, follow "bass drum volume" seen at upper center on page 14. It references feeding R271 on another page. Note upper page 15, U237 is fed signal from prior section through 10K R271. So that looks to be your volume instruct path, and you can determine from there is the fault is down or up stream.

[cutoffres]

Thanks a lot.
I misspoke: no volume control or tuning works on any of the sounds. So i can't compare with working channels as it is impossible to set individual TUNING or VOLUME on all the individual sounds.
That is why i suspected U226 DAC (7524) and replaced it without success.
Your idea to test with MIDI and pitch bend is a good one. I've tested to play the Drumtraks with a MIDI keyboard and play with the pitch bend, it works, i don't have all the 15 different tuning settings by instruments but I'm able to get a few different tuning settings per all instruments.
So, any other idea? Where to check to get back working the individual VOLUME/TUNING per instrument working from the pots on the Drumtraks itself?

[crochambeau]

Does either "per instrument" panel control indicate a value change on the numerical display when you adjust them while holding a drum pad/sound switch?

If MIDI is working I would say the functional aspects are in place, and it might be as simple as a failed or really dirty pot? Something user interface or front panel to sound board related.

I fired my machine up after replying and discovered I have no sounds at all (beyond metronome), so, here's to digging into old SCI. R.I.P. Dave Smith.

[cutoffres]

Does either "per instrument" panel control indicate a value change on the numerical display when you adjust them while holding a drum pad/sound switch?

NO, it indicate a value only when triggering sounds in MIDI.

All the four pots have been replaced by new one.
And just replaced U218 without success.
Thank you.

[crochambeau]

Does either "per instrument" panel control indicate a value change on the numerical display when you adjust them while holding a drum pad/sound switch?

NO, it indicate a value only when triggering sounds in MIDI.

All the four pots have been replaced by new one.
And just replaced U218 without success.
Thank you.

I meant to quote this part "Could it work in MIDI if U218 where faulty?" but it seems you beat me to it..

I believe MIDI is just going to take a note input and trigger that corresponding sound. That you have the tuning (and presumably level (?)) control via external MIDI instruction just proves that the function works in relation to the sound engine. We can therefore ignore the VCO as culprit at the moment.

What diagnostic tools do you have on hand? I assume you have a multimeter, do you have an oscilloscope?

I ask because just ripping through ICs and replacing stuff without evidence of fault can get costly, and I'm no good at that method.

The two panel pots in question feed the 4053 U101. The 4053 switch is driven by U216, and feeds U225. I would start my hunting at the 4053, if it's switching and you can measure the voltage reference (from pots) through it you know the disconnect is downstream, if it's latched into just one state the issue is upstream.

[cutoffres]

Got a scope, but didn't found evidence of fault so replaced some integrated circuits of the individual tuning that i had under the hands.
My question:
How to check with scope if the 4053 is switching? Or if it is latched?

[crochambeau]

Got a scope, but didn't found evidence of fault so replaced some integrated circuits of the individual tuning that i had under the hands.
My question:
How to check with scope if the 4053 is switching? Or if it is latched?

I opened my machine up so as to not be talking out my a*s here, and since U101 4053 is on the upper panel board I found it MUCH easier to simply measure the result at pin 7 of U225, the destination point for the work done at the 4053.



There is a pulse about 100 μs long, volume adjusts the pulse height, tuning adjusts the background DC level the pulse rides on. At least, that's what my machine does - please bear in mind that my machine is also malfunctioning - but the voice tune and volume were working last time I used it.

Anyway, if you can see your signal shift when you rotate either control then it stands to reason the 4053 is doing its job (which is just switching between the two pots really fast).

[cutoffres]

There is a pulse about 100 μs long, volume adjusts the pulse height, tuning adjusts the background DC level the pulse rides on. At least, that's what my machine does - please bear in mind that my machine is also malfunctioning - but the voice tune and volume were working last time I used it.

Anyway, if you can see your signal shift when you rotate either control then it stands to reason the 4053 is doing its job (which is just switching between the two pots really fast).

Yes, same results.
Thanks a lot for the very clear explanation, now i understand how the 4053 works.

Then i presume that the problem is after U225 or at U225?

(i understand that your drumtraks don't works now, and i will help i you need measurement with the part that works good on mine)

[crochambeau]

Then i presume that the problem is after U225 or at U225?

I think U225 is going to be easy to troubleshoot. Pin 5 acts as output. There should be two pulses, "volume" affects the width of the first pulse, "tune" affects the width of the second.

That signal is feeding U211, which is going to count 2 MHz pulses while the gate (pin 16) is high - first for volume, then for tune. That section deadheads its direct output (NC on pin 17), so the digitization of the values are going to to be output on the data bus buffer (across 8 pins) to interface with CPU.

At this point, for me to keep up, I would need to break out a data analyzer and figure out how to use it (I need to do this anyway, it'll just slow me up). My armchair theory is that since you can tune via MIDI, the micro-processor and beyond aspects of that are solid. Leaving the data bus from U211, and whatever other linkage is in the path there.

I think the CPU directs what "goes live" (to be measured) and when, so seeing two consecutive pulses at pin 5 of U225, we can infer that the U211 data bus at those moments (or immediately thereafter) is communicating direct, but I'm a bit fuzzy on this level of digital troubleshooting - so I hope I'm not steering you wrong.

(i understand that your drumtraks don't works now, and i will help i you need measurement with the part that works good on mine)

Thanks! It appears as if I've lost the negative power rail in the analog end of things. Far more suited to my comfort zone.

[cutoffres]

There is nothing on U225 (74LS221) pin 5. So there are great chance it is the culprit? Do you see two pulses on your machine?
Also it looks like U225 is related to the metronome, then it may be also the culprit of the second problem i have on the machine concerning metronome missing beats.
I'm going to order an 74LS221 and replace U225, will see if it solve the problem.
Thanks a lot crochambeau, i think you brought me back to the right path!

[crochambeau]

There is nothing on U225 (74LS221) pin 5. So there are great chance it is the culprit? Do you see two pulses on your machine?
Also it looks like U225 is related to the metronome, then it may be also the culprit of the second problem i have on the machine concerning metronome missing beats.
I'm going to order an 74LS221 and replace U225, will see if it solve the problem.
Thanks a lot crochambeau, i think you brought me back to the right path!

Yeah, I see two pulses on pin 5 of U225. The width of each pulse is tied to each of the knobs that are non-functional on your machine. It does seem like a very possible failure point, good luck!

[cutoffres]

I've replaced U225 and it is better but still faulty:
Now the display indicate number of setting from 00 to 15 when i move the TUNING or VOLUME pot; but i can hear only two different tuning on the bass, two different tuning on the snare.
On most other sounds i can hear only 3 or 4 different tuning, 7 different tuning settings on the clap...
And concerning the individual volume, the pot affect the display(from 00 to 15) but it do not affect the volume in that you can hear. The individual volume do not change whatever it is set to 00 or 15.
So i continue to troubleshooting, if you have any ideas it will help.

Also on some ic i've replaced the original 40174 ( IC16, IC17, IC18) with 74LS174 could it be an other problem of clock speed using that ic?
Thank you.

[crochambeau]

Remind me, do you have the full range of sound tuning via MIDI external control? Or just the levels you now have at your fingertips?

You indicate you see the tune/vol range from 00 to 15 on panel display, I conclude that lands on each value? Yet, the actual result only hits some of the settings even though the panel display is indicating all 16 levels.

It sounds like the analog to digital side of the control knobs is solid, and can, for the time being, be ignored as operational. Sounds to me like the focus is really getting mired in the middle of digital lines, which is not my comfort zone. So, I'm happy to throw out an idea here or there, but this is just stabbing in the dark territory (something I consider unhelpful most of the time).

Volume, I believe, is a product of voltage level on pin 11 of the 6070. I guess at this point I would start working backwards from the DACs and see what can be found.

That everything is being wonky does lend credence to the notion that it's a shared part or system. How does the clock line look?

[cutoffres]

Remind me, do you have the full range of sound tuning via MIDI external control? Or just the levels you now have at your fingertips?

No, i don't have the full range via MIDI, i just have exactly the same levels as with the potentiometer.

You indicate you see the tune/vol range from 00 to 15 on panel display, I conclude that lands on each value? Yet, the actual result only hits some of the settings even though the panel display is indicating all 16 levels.

Yea the 16 TUNING levels are indicated on display but in reality i can hear only 2 tuning level on BASS & SNARE, No tuning on RIM; 4 tuning level on TOM1, 4 tuning level on TOM2; 4 tuning level on CRASH; 3 tuning level on RIDE; No tuning level on OPEN & CLOSED HIHAT; 7 tuning level on CLAPS; 7 tuning level on TAMB; 4 tuning level on COWBEL; 7 tuning level on CABASSA.

And concerning VOLUME i see 16 level on display but i can only hear one volume level on every instruments.
You explained well and i understand a lot more with your help.

That everything is being wonky does lend credence to the notion that it's a shared part or system. How does the clock line look?

Got difficulties to set correctly my little portable scope to measure frequencies but with the same oscilloscope settings i measure 4MHZ on U205 CPU pin 6; 4MHZ on U221 pin 12; 2MHZ at U221 pin 9 and U211 pin 18.

Volume, I believe, is a product of voltage level on pin 11 of the 6070

I've got 00V on all 6070's pin 11.