Accent and decay not working, please help

[bryeng]

Hi,I've just finished building my x0xb0x and all tests went fine. I couldn't measure a pulse on the envelope test but could hear a note played when probed with an ear phone.
The x0xb0x al works fine apart from the accent button not having any effect on the notes payed. Also the decay pot doesnt apear to do anything. Stupid question, but does the decay effect the decay of the note played or the filter. On my x0xb0x the notes decay very quickly when played with the decay pot not changing anything.
I've taken the following voltage readings from IC12 and some transistors:

IC12
1 0.026 14 11.86
2 0.026 13 0.02
3 0.05 12 10.73
4 0.05 11 2.75
5 0.019 10 2.75
6 0.044 9 2.75
7 0 8 2.73

Transistors (left to right with flat facing me)
Q39 0, 0, 0.026
Q41 0.03, 11.86, 0.3
Q40 0.32, 11.86, 0.34
Q30 0, 0.05, 0.59
Q29 0, 10.73, 0
Q38 11.86, 0, 11.85
Q36 11.86, 0, 11.85
Q37 0, 11.84, 0
Q8 8.44, 6.81, 8.83
Q27 11.86, 0, 11.27
Q25 7.52, 11.26, 0.18
Q28 8.29, 8.08, 11.86
Q26 5.33, 5.33, 4.78, 8.08, 5.27
Q24 5.36, 0.17, 0.32

I can't see any dry joints or shorts, not to say that there aren't any. Do the following readings suggest a short, a broken IC12 or a broken transistor?
Thanks for any support anyone may have to offer with this!

[MMM]

Just to make sure we're on the same page:

The decay pot doesn't do anything in normal mode or in accent mode? Does the accent pot have any effect (both for normal notes or accented notes)?

[bryeng]

Sorry I wasn't very clear in my post.

The decay pot doesn't do anything it the accent button is on or off. The accent button doesn't have any effect on the sound either, thats if its in a sequenced track or in play mode. As the accent button doesnt seem to do anything therefore the accent pot has no effect either.

Thanks for the quick response.

[MMM]

Let's see if the accent control for IC12 works.

We're doing the measurements in keyboard mode.

Press "accent" (so it's lit) and a note afterwards (this is important). Now measure Pin 13 and 5 of IC12. They should be at about 12v. Press again "accent" (so the LED goes off), press again a note and check if there are 0v at pin 13 and 5. If both is the case it at least means that the accent control line reaches IC12.
If you don't get those voltages (approximately) please follow the same steps and measure the "bottom" end of R41 (the one closer to the processor) instead.

[bryeng]

I've checked IC12 and I get 11.74V at pins 5 and 13 when accent is on and get 0.02V at pins 5 and 13 when accent is off. So at least that part's working!

While I was doing this I also checked IC11 and got the following:
With accent off
1 4.62
2 5.33
3 5.33
4 0
5 2.89
6 2.92
7 2.92
8 11.86

with accent on
1 4.62
2 5.33
3 5.33
4 0
5 2.56
6 2.59
7 2.59
8 11.86

Don't know if that helps any but thought I'd do it while I was poking about!

Any ideas on where to go next? Does this suggest that IC12 (4066) is broken?

Thanks again for your help.

[MMM]

Yes, it looks as if the control signal reaches IC12.

Now let's try the following: Using the same strategy as above (pressing "accent" and a note afterwards) please measure the resistance between pins 1 and 2 and between pins 3 and 4 of IC12 for both scenarios (accent active/inactive).

[bryeng]

ok

WIth accent off I get:

Pins 1-2 66.6Kohm
Pins 3-4 3.6ohm

With accent on:

Pins 1-2 73.2ohm
Pins 3-4 3.4ohm

[MMM]

There definitely is something wrong with pin 3-4. The resistance should shift significantly depending on the accent state. What you observe is at least partly consistent with the problems you've witnessed.

What I can't say for sure is if IC12 is to blame or if there is another problem (perhaps with the PCB itself). At this point I'd suggest removing IC12 and then measuring the resistance between the solder pads for pin 3 and 4.

[bryeng]

Right, before I started anything I noticed that one of the solder joints looked a but dodgy on the decay pot (VR7). I re-soldered this. I've still got all the same problems with the accent and decay not doing anything but now when I measure IC12 I get:

With accent off
Pin 1-2 66.7K ohm
Pin 3-4 105.4K ohm

WIth accent on
Pin 1-2 74 ohm
Pin 3-4 76.7 ohm

then with IC12 removed from the board

With accent off
Pin 1-2 36.9K ohm
Pin 3-4 191K ohm

With accent on
Pin 1-2 37K ohm
Pin 3-4 191K ohm

I think I may have helped things by re-soldering the pot, but the fault with accent remains.......

[MMM]

OK, I think IC12 may not be the problem here.

I'd propose working on this one problem at a time. First we'll try to fix the Decay problem; and then we'll address the Accent issue.

Now, interestingly without IC12 the xoxbox should basically still work. IC12 is responsible for enabling the slide and the accent; without IC12 neither can be enabled. Which also means that the basic functionality should be there; especially Decay should work as normal.

Please make the following settings: Cutoff half, Resonance max, Env Mod max, Decay max.

Do you observe any envelope movement, like a filter sweep? Even a short one? Does this change if you move the Decay pot to a different position?

Do you have by chance access to an oscilloscope?

[bryeng]

Set the x0xb0x as you stated.

Hard to describe (not sure what you mean by a filter sweep!), but I just hear a simple note played when I press a key.

If the note is held down, I the note decays away after a number of seconds. This decay of the note is not changed if the decay pot is put in any other positions.
If the note is quicly pressed on and off, the note just quickly plays. Again with decay having no effect.

I have access to a oscilloscope at work, so can take readings with that. Should even be able to take screen shots from the scope and post them.

Please let me know what measurements you want me to take.

thanks

[MMM]

That's the normal behaviour for the loudness envelope - that one is not affected by the Decay knob. "Filter sweep" means that the sound of the note changes significantly over time, kind of like a "wow" effect (depending on the position of the Decay knob and the Env Mod knob).

Another test: Cutoff half, Resonance max. Play a note repeatedly and move the Env Mod knob. Does the sound change; and if so, how?

[bryeng]

Ok got what you mean with the filter sweep.

With cutoff half, resonance max: When env mod is turned (again hard to describe) but as i turn it from min to max the note changes from a "harder sounding note" to a "softer filtered note". The effect of turning this pot is very noticable.

[MMM]

And different positions of the Decay knob make no audible difference to the quality of the sound?

[bryeng]

No, different positions of the decay knob have no effect when doing this.