Finished X0xbox, but no sound -> SOLVED

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Foobn
 
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Finished X0xbox, but no sound -> SOLVED

Post by Foobn »

Hi guys,

i finished my X0xbox from x0xshop.de and now have some failures, where you may can help me.
I followed the topic http://www.adafruit.com/forums/viewtopi ... 12&t=39292 which seems to describe a similar problem.

The digital side works fine (after I flashed the Atmel myself; seems it was not flashed before shipment)

Pin 7 of IC11 show 2,16V to 3,12V depending on the key stroke. J4 has the correct voltage. As I see the saw and the square, I assume to have a failure in the VCF area.

If I plug my Oscilloscope to C14 I see a clear signal which changes depending on the knob settings.
On the right side of R62 I see the saw, but on the left side of R62 I see nothing. I have 6,8V on the left side, but no signal. I already changed r62, but no change.

Do you guys have any hint I can try?

Best regards
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Last edited by Foobn on Mon Aug 19, 2013 7:57 pm, edited 1 time in total.

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antto
 
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Re: Finished X0xbox, but no sound

Post by antto »

R62 is right on the VCF input
so the saw/square (which is a rather strong signal) goes on one side, but on the other it becomes uber weak, because R62 is 220k Ohms
so that's normal, just adjust your voltage scaling if you're using an oscilloscope and you'll see it
more important is that you see the output at C14 being a saw/square looking like being filtered by a resonant LPF - if you can see that, then everything so far is good

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mmm
 
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Re: Finished X0xbox, but no sound

Post by mmm »

Foobn wrote: If I plug my Oscilloscope to C14 I see a clear signal which changes depending on the knob settings.
As antto wrote this means that the VCO and VCF are probably working fine. Which means the problem might lie with the VCA or its controlling signal.

Please check what happens at the innermost pin of the volume pot when playing a note.

Foobn
 
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Re: Finished X0xbox, but no sound

Post by Foobn »

Thanks for your quick reply.

I should not use the Oscilloscope in the middle of the night.

So R62 is fine. If have a clear output here. Also i checked again the resonance pod. Good signal here on min and max settings.

I checked (-) of C38 and the middle pin of the Volume pot. No clear signal here (bandwidth limit on on the Oscilloscope)

I printed the PCB plan and check everything between. Any ideas where I should start?

Thanks again for the help.

Best regards
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mmm
 
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Re: Finished X0xbox, but no sound

Post by mmm »

Please check if you're getting a signal on pin2 of IC15B (you'll need to measure this with an AC coupled scope).
Then measure the voltages on IC15B with a multimeter. Also measure what happens at pin4 of IC15B when pressing a note button.

Foobn
 
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Re: Finished X0xbox, but no sound

Post by Foobn »

Hi,

i used the lunch break to make some very quick checks.

IC15B
1 - 5,3 V
2 - 5,3 V
3 - 0 V
4 - 0V, 11,89 if key is pressed
5 - 0V
6 - 5,03 V
7 - 5,03 V
8 - 5,33 V
9 - 11,91 V

There is no signal on Pin 2 (checked with AC mode on)

I quickly checked some lines and found the signal on C21, R67 and R99. But more checks must be done at night when I have time.

Best regards
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Attachments
C21 right.jpg
C21 right.jpg (34.59 KiB) Viewed 1254 times
R62 high C.jpg
R62 high C.jpg (35.5 KiB) Viewed 1254 times
IC15B Pin2.jpg
IC15B Pin2.jpg (41.49 KiB) Viewed 1254 times

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mmm
 
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Re: Finished X0xbox, but no sound

Post by mmm »

Foobn wrote:Hi,

i used the lunch break to make some very quick checks.

IC15B
1 - 5,3 V
2 - 5,3 V
3 - 0 V
4 - 0V, 11,89 if key is pressed
5 - 0V
6 - 5,03 V
7 - 5,03 V
8 - 5,33 V
9 - 11,91 V

There is no signal on Pin 2 (checked with AC mode on)

I quickly checked some lines and found the signal on C21, R67 and R99. But more checks must be done at night when I have time.
OK, my mistake: It's pin1, not pin2 that carries the signal.

But that's probably not too important, because this
4 - 0V, 11,89 if key is pressed
is way off. From the latest experiences this hints at a problem with IC15B; or possibly a problem with the current mirror. But my guess would be IC15B.

Foobn
 
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Re: Finished X0xbox, but no sound -> SOLVED

Post by Foobn »

Your guess was right.

I had 4 BA6110 and 3 of them were broken. I tried a new one from xoxshop and now I have a tone.

Not exactly xoxbox or TB like but this is now fine tuning.

Thanks a lot for the help!!!!

Best regards
Jedo

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