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Xox new build not working
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Xox new build not working

by xtals on Sat Sep 02, 2017 5:24 pm

Hi to everyone! :)

I've almost finished building my xox (everything but leds and led resistors)
Unfortunately nothing works: I have the correct voltages at the main pcb connector, checked all the electrolytic caps, ic's, transistors and checked for shorts: all seems to be fine.
Where you suggest to start checking?

Thanks!

xtals
 
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Re: Xox new build not working

by antto on Sun Sep 03, 2017 3:34 am

it would help if you give some more details
where did you get your x0x kit from
did you perform the varios tests during the build process
what exactly doesn't work right now, and what does work

antto
 
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Re: Xox new build not working

by xtals on Sun Sep 03, 2017 9:23 am

Hi!

i have a willzyx kit!
During the building process i didn't had a scope (but now i have it), so i performed
the tests described in the ladyada manual with multimeter and variable bench power supply.
I've put the xox in keyboard mode, pots at 50%...no sound at all.

xtals
 
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Re: Xox new build not working

by xtals on Mon Sep 04, 2017 10:32 am

No suggestions? :(

Double checked all resistors too...everything ok.
It would help if i check the analogue section voltages as shown at the eagle file in the sticked thread?

Update:

I've checked the waveforms with the scope:

square is present at the waveform switch pin with 3.90vpp
sawtooth is present at R105 with 5vpp

xtals
 
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Re: Xox new build not working

by antto on Mon Sep 04, 2017 12:35 pm

that's good
follow the audio signal along the path
check that it reaches the filter, and that it gets filtered and goes out
check that it reaches the VCA

now, the VCA is the amplifier, it normally mutes the output ..
check that the sequencer generates the expected signals - specifically Gate, and Pitch (you can check that after the resistor network, or at the pitch CV output jack (you need the corresponding jumper cable between the two PCBs to be connected for that)

if all of that checks out fine, and you're still not getting sound - we shall think further

antto
 
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Re: Xox new build not working

by xtals on Mon Sep 04, 2017 2:24 pm

Thanks!

So I can start doing again this test as described in the manual:

Connect power from the IO board and provide 2.0VDC to R90, as before.
In a quiet room, connect up a pair of low-fi (32ohm or greater impedance) headphones as before: ground the sleeve, and use the tip for probing. Touch the tip to rightmost pin (the one that is not connected to the ground plane) of where the volume potetiometer VR8 will go.

Am I right?
And then I will follow the remaining signal path.
I don't have that kind of headphones, so I will use the scope for that!

xtals
 
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Re: Xox new build not working

by antto on Mon Sep 04, 2017 2:48 pm

if your sequencer is populated, then be careful with the tests from the build manual
the build manual goes section by section, and some (many) of the tests assume that the following sections are not populated yet
so it instructs you to inject some voltage at some place.. but if the following section is populated - you would inject voltage into something that already outputs a voltage.. this can result in a short circuit

anyways.. injecting 2V at R90 is meant to give you some pitch for the VCO
if you got a sequencer already in there, the sequencer should provide pitch
so measure it with a multimeter.. for example at J6 - pin1
you can use Keyboard mode to get the sequencer to produce something about 2 to 3V
the reason for this is because, if the pitch voltage is too low, the VCO will oscillate so slowly that it would not seem like it's oscillating at all, and if it's too high it might get completely filtered out by the VCF

antto
 
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