Old x0x never been tuned (solved)

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isak
 
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Old x0x never been tuned (solved)

Post by isak »

Hi x0xers

I'm trying to Tune an old x0x that never been tuned.
It's strange, gives me very low notes even below C0 and I can't get it higher then C2.
I checked the 200k's resistors, looks kosher to me, maybe ic9 is the problem? The IC's are not socked so I'm trying not to desolder any IC's.
I get 5.33V from j4.

What do I need to check?

Cheers,
Isak E.
Last edited by isak on Mon Apr 29, 2013 6:14 pm, edited 1 time in total.

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isak
 
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Re: Old x0x never been tuned

Post by isak »

I think the problem starts from the I/o board, today I checked the V on j4 and I got 5.30V to 5.31V after trimming it yesterday to 5.33V
But yet again I don't think it's only the I/o, it continues to the mainboard as well.

Any one?

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mmm
 
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Re: Old x0x never been tuned

Post by mmm »

Please check all voltages first; do this on the mainboard (you can measure directly at the connector from the IOboard).
If they are roughly in the ballpark put the xoxbox in keyboard mode and measure the voltage on pin7 of IC11 while playing low and high C (non transposed). Please report back your findings.

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isak
 
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Re: Old x0x never been tuned

Post by isak »

hi mmm and thank you for your reply.

j4 on the mainboard is ok, i get 5.33V and 11.87V.
pin 7 on C1 gives me 1.01V at highest gives me 5.01V.
in all octaves it gives me good V results.

what next?

another problem i found is that it doesnt have midi in, the midi out and midi thru is working great, but no midi in.
i found this thread and follow dear guest directions
http://forums.adafruit.com/viewtopic.php?f=12&t=21479
i'v check all the wires, all seems to be ok.
one thing tho...from the junction of Q50 and r15 to pin 10 of the microcontroller i get 0.4 ohm when guest said it haves to be 0 ohm, if it helps somehow.

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mmm
 
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Re: Old x0x never been tuned

Post by mmm »

As far as your tuning problem goes: The results show that IC9 is not faulty and that everything up to this part of IC7 is ok. Which means we need to dig elsewhere.
I'd probably check all the parts on the "left side" (in the schematic) of Q26. TM4 and so on.

The MIDI IN problem is comparatively easy to debug if you have an oscilloscope.

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isak
 
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Re: Old x0x never been tuned

Post by isak »

i think i found the problem!
its the BANNED, they are not BANNED!
ill check it and let you know.

i dont have a scop but i have a multimeter, can i check with that?
if yes what should i check?

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isak
 
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Re: Old x0x never been tuned

Post by isak »

this is how they looks like.
they dont look like BANNED to me, please correct me if i'm wrong..

Image

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pulsar256
 
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Re: Old x0x never been tuned

Post by pulsar256 »

The color coding of these presumably genuine PTC resistors looks about right. I take it the second ring from the bottom is actually dark green. Each of these has about ~1k, so in parallel you should measure about 500Ω, in-circuit I've got ~480Ω.

To be honest, I have no Idea what gives those types away in comparison to normal 5 band resistors. When compared to the pictures over at willzyx's they do look just about right: http://www.willzyx.com/products/1k-ptc-thermistor

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pulsar256
 
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Re: Old x0x never been tuned

Post by pulsar256 »

One more thought: I take it, you did already try to follow the VCO tuning guide according the the build instructions? I mean, applying test voltages to R90 (You will need to use R89 instead, since your R90 is mounted the "wrong" way), centering TM4 and adjusting the octave width with TM5?

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isak
 
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Re: Old x0x never been tuned

Post by isak »

Thanks for replying.

I didnt build this x0x, I got it for fix.
I have 4 new BANNED from x0xsh0p, they are deferent color code, instead green it have black in the end, I think more color are not match.
I'll try to replace them and see if it's helping somehow.
I know how to tune the x0x, I did it more then ones or twice in my life ;)
If the replacament of the BANNED wont help I really don't know what to do next.

I'll try to do the building manual tests, thanks :)

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pulsar256
 
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Re: Old x0x never been tuned

Post by pulsar256 »

BANNED from x0xsh0p (.de) have very dark green bands which look almost black to the eye. I've just checked these under my magnifying glass lamp.

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isak
 
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Re: Old x0x never been tuned

Post by isak »

Really? I need to take another look :shock:
Have you maybe notice that there is deferences of the head of the wire?
I mean where the wire connected to the boudy if the resistor.
From willzyx it's looking like regular resistor, from x0xsh0p the base of the wire is wider.
anyway I guess both are the same.
Moving on, what to check?

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pulsar256
 
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Re: Old x0x never been tuned

Post by pulsar256 »

take a look:
2x 1k PTC
2x 1k PTC
2013-04-11 20.55.38.jpg (172.33 KiB) Viewed 2495 times
In comparison to standard resistors, the wiring ends up in a metal cap. Also note, that my mobile phone does not make the best photos in terms of color, the bands are green. Upper one very dark, bottom one is a bit lighter green. Still dark.

I would still start troubleshooting the VCO by injecting 1-3V directly between R90 and R89 to rule out everything behind the uC / DAC. But since I am just building my first x0xb0x, I should rather shut up and let more experienced troubleshooters give you a hand here :)

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isak
 
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Re: Old x0x never been tuned

Post by isak »

thanks for the pic.

you mention that both BANNED should give me about 500hom, right?
well they give me 1k, this is was suspicious to me, i solder both out and measure them one by one, the first is ok, gives me 1k as it should, the second didnt give me reading at all!
my guess that its a bad Tempco, go figure, with all the troubleshooting there is i bumpt to a bad Tempco :x

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pulsar256
 
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Re: Old x0x never been tuned

Post by pulsar256 »

Perhaps soldered too hot? we'll never know. The construction manual mentions to be careful with these. Good hunch!

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