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Killed my xoxbox! Help if you can?

by echoditto on Sat Dec 22, 2012 2:55 pm

Hi guys... So- I am a jackass.
I just got a used xoxbox, and I was so excited. I played around
and realized that half the tact switches needed to be cleaned or replaced
and that it needed to be calibrated because it was awfully out of tune.
I have a multimeter and it didn't sound difficult, so I opened it up,
sprayed the tact switches with some deoxit (which worked beautifully),
used the trimpot to adjust the power supply to 5.33, messed with the
tm5 and tm4 pots till I had at least 2 octaves relatively in tune, and I should have
stopped there. Unfortunately I did not. I decided (after getting a bit stoned)
that I could do better with the tuning. I thought that maybe I had tuned it too low, and
that explained the major slippage that was still occurring, so I reopened it, tried again,
did a better job, and then started admiring the circuit board. I said to myself, "oh, how lovely...
Look there! Those resistors seem to be touching! I should separate them just a bit"
and whatever the hell I did, apparently killed it. When I applied power again, all the lights came on and
stayed steady and nothing had any effect. I tried find the resistor cluster again and looked all over
for another reason... I tried to tell with the multimeter whether I had loosened one of the ribbon cables...
I stared at it for like two hours, and now upon receiving power all the lights come on and then
just the tempo light stays lit steadily.
Any idea at all how I could start to figure out what went wrong?
I bet I blew up some chips or something as well... :-(
Take pity on me, please. I would love to fix it.
Thanks in advance
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by MMM on Thu Dec 27, 2012 5:58 pm

Do you have access to an oscilloscope?

Don't worry, I've not yet seen a xoxbox that couldn't be fixed.
MMM
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Thu Dec 27, 2012 6:38 pm

I do have access to an Oscope!
You are my hero!
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by MMM on Fri Dec 28, 2012 7:15 pm

So, what we need to find out is if the processor is actually running.

Make sure the xoxbox is in "Pattern Play" mode, and then measure the following pins of IC3 (the processor):

pin 40
pin 9
pin 18
pin 19
pin 1
pin 32

You need to use the oscilloscope in "DC coupled" mode for this.
MMM
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Sun Dec 30, 2012 4:48 pm

alrighty!
no idea if I was doing it properly, but-
holding the alligator clip end of my probe to pin 20 (gnd),
and touching the others as directed, I saw the following:
pin 40) 4.80v
9) 4.80v
18) 320.00mv
19) 560.00mv
1) 4.80v
32) 4.80v

if I was doing it wrong, or should select another measurement option,
please let me know! I had not used a scope for anything other than
viewing an audio signal thus far, so... I was kinda guessing.
THANKYOU!
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Sun Dec 30, 2012 4:50 pm

oh, and pattern play mode is "pattern (sync out)"?
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by MMM on Mon Dec 31, 2012 4:35 am

echoditto wrote:oh, and pattern play mode is "pattern (sync out)"?


Yes, that's the correct one.

echoditto wrote:alrighty!
no idea if I was doing it properly, but-
holding the alligator clip end of my probe to pin 20 (gnd),
and touching the others as directed, I saw the following:
pin 40) 4.80v
9) 4.80v
18) 320.00mv
19) 560.00mv
1) 4.80v
32) 4.80v


In general the first four measurements look ok (albeit a tad bit low - however this could easily be the resolution of the oscilloscope).

For pin 32 it would be important if there is some kind of pulse or if this is just 4.80V DC. Please check pins 6 and 8 as well; you may have to set the horizontal resolution of the oscilloscope to less than 1ms for the pulses to see.
MMM
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Sun Jan 06, 2013 2:15 pm

sorry it has been a few days!
I have been trying to figure out this oscilloscope when I can and either I am
failing or pin 32 is not oscillating...
the scope goes from 50.0V to 20.0mVbw and time from 50.0s to 20.0ns.
can you suggest a setting to me?
and holding the alligator clip end on ground (pin20) is the way to go?
:oops:
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Sun Jan 06, 2013 2:15 pm

and happy new year!
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by MMM on Tue Jan 08, 2013 6:51 am

echoditto wrote:sorry it has been a few days!
I have been trying to figure out this oscilloscope when I can and either I am
failing or pin 32 is not oscillating...
the scope goes from 50.0V to 20.0mVbw and time from 50.0s to 20.0ns.
can you suggest a setting to me?
and holding the alligator clip end on ground (pin20) is the way to go?
:oops:


Yes, that's all ok.

A possible setting would be 5V or 2V vertical and 500ns horizontal; this should show the pulse (unless the triggering doesn't work). Many scopes have an "autoset" feature that tries to guess the resolution and the triggering setup; you may want to try this as well.
MMM
 
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Re: Killed my xoxbox! Help if you can?

by synthplayer on Wed Jan 09, 2013 12:34 am

Some food for thoughts, do you get sound in RANDOM mode?

If you have a CRO then go into RANDOM mode and have a look at pin 7 of IC11, You should see a stepping DC in the range of 0-5V with each change of note(OSC CV). This verifies that the MCU is working in the right mode and no sound means, the problem exists in your synth circuit section. You might then want to

Check VCO for output
1. Measure with a meter in AC mode or better yet, look on the CRO at node R62 connecting to the WAVEFORM switch to see if you have SAW and SQUARE wave.

Check VCF for output
2.Measure with a meter in AC mode or look on the CRO at C14

Check VCA for output
2.Measure with a meter in AC mode or look on the CRO at C38(Volume pot pin 3)

You should get at least >1V signal at all of these points.
synthplayer
 
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Re: Killed my xoxbox! Help if you can?

by echoditto on Wed Jan 09, 2013 9:47 am

Alright! I will have a chance to try all of these things this evening I hope.
What is a CRO, though?
oscilloscope?
Thank you both-
echoditto
 
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Re: Killed my xoxbox! Help if you can?

by synthplayer on Wed Jan 09, 2013 10:18 am

Yes, CRO stands for cathode-ray oscilloscope.
synthplayer
 
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