Built Xoxbox // NO SOUND

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

At the cathode of D27 you should get more or less 0.5V which will then decrease over time (that's the slow decay of the volume envelope); at pin 4 of IC15 you should get a similar behaviour but starting with about 1.2V. In both cases the voltage will drop to zero (or nearly zero) when the note button is no longer pressed.
I suspect the problem in the general area of Q1 to Q4. Please check thoroughly, especially for the correct parts and possible solder bridges.

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

got the correct voltage on D27, which is around 0.5V.
I've triple checked Q1 to Q4 components (types, directions and solder joints), they seems ok.

What kind of test should i try to verify that Q1/Q4 are faulty ?

Many thanks, I owe you a beer if you go to Paris! :)

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

Is there always about 12V on pin4 of IC15B or only when playing a note?

I would suspect Q1 and Q2 here; perhaps the easiest way would be to desolder them and check them with the multimeter (if it has a transistor tester).

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

12V on pin 4 only when a key is pressed.

ok, for the transistors, my multimeter should a transistor tester. iI'll desolder Q1 & Q2 and let you know.

Thanks!

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

Hi there!

I've desoldered Q1 & Q2 (it was quiet paintfull, so i've put some sockets there).
I've tested both transistors:
Current flows from emitter/collector legs to base leg as it should (PNP) and only on that direction.
To my mind, Q1 & Q2 seems to be ok.

Any thought?

I'll do the same thing with Q3 & Q4 to see if i have a different result.

I've also ordered some remplacement parts from xoxshop.de to help me to resolve my issue (few 2SC536F, 2SA733P and BA6110), then i could make tests with the new components.

Thanks for your great help! ;)

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

The problem with this particular circuit is that it is not voltage controlled; it is current controlled. The voltage changes we observe are the results of current changes (or at least they should be).
Q1/Q2 and Q3/Q4 are so called "current mirrors" that essentially "forward" the current coming from the envelope.
There are a number of things that could be faulty here.
One possible scenario would be the second half of the Q1/Q2 mirror failing for whatever reason. Let's see how far the envelope comes:

Remove just Q1 (since you have them socketed this should be no problem) and measure all three solder pads/socket pins without playing a note.

The emitter pad should be at the 12V rail voltage (which most of the time isn't exactly 12V but that's not important).
The collector pad (which connects to IC15B) should be close to zero.
The base pad should be about 0.5V beneath the 12V rail.

Now play a note. The measurements will depend a bit on the internal impedance of the multimeter. You should see a slight drop (about 0.1V or less) of the voltage at the base pad.

Does that work so far?

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

ok, great infos! Thanks.

here are my measures:
Image

with no keyboard note pressed:
Red leg (base): 11.28V
Blue leg (collector): 0V
Green leg (emitter): 11.78V

When a note is pressed:
Red leg (base): drop to 11.10V and then goes back to 11.28V
Blue leg (collector): 0V (no change)
Green leg (emitter): 11.78V (no change)

it seems to behave as it should.

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

Yes, seems good.

This points finally to IC15B. Please measure the voltage on all pins of IC15B.

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

here they are on IC15B when no key pressed:

1 -> 5.33V
2 -> 5.33V
3 -> 0V
4 -> 0V
5 -> 0V
6 -> 5.33V
7 -> 5.33V
8 -> 5.37V
9 -> 11.75V

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

Please check the following:

Do have both pin 3 and 5 connection to ground? Does by chance pin 4 have also connection to ground (it shouldn't)?

Finally: Install Q1, but without the emitter (bend it so that it is outside the socket) and measure what happens at this emitter when playing a note.

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

Pin 3 & 5 are connected to ground.
Pin 4 is not.

with Q1, when emiter is out of its socket:
no key pressed:
-> 3.6V

when a key is pressed:
Voltage drops to around 3.4V and goes back to 3.6V.

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

My mistake: Please test above Q1 scenario without the collector in the socket (and measure at the collector leg).

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

no problem! :)

so, on the collector leg, it happens the same as on pin 4 of ic15B:
when a key is pressed, voltage raises from 0V to 11.75V and then drops to 0V.

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mmm
 
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Re: Built Xoxbox // NO SOUND

Post by mmm »

Well, that all looks good (same behaviour as on my machines) which pretty much points at IC15B itself as the possible source of trouble.

sequentialmood
 
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Re: Built Xoxbox // NO SOUND

Post by sequentialmood »

Ok, i really appreciate your help and great expertise.

i'll wait to receive a new BA6110 from xoxshop.de to test if the one i got is faulty.
I'll let you know soon. :)

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