Dodgy MIDI Channel Selector Knobs

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midiquestions
 
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Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

I bought a x0xb0x a few months ago off of eBay, and while I absolutely love the sound, whoever put it together did a terrible job. The volume knob doesn't go all the way down to zero, it wasn't tuned properly, etc. -- there is quite a list of troubles.

However, one of the biggest problems that I am facing right now is that when I put the x0x into MIDI mode to be played as a sound module, the 1-16 rotary knob isn't stable. Left to its own devices, it only selects channels 1-8, then selects channels 1-8 again when you scroll around to 9-16. If you kind of push and pull on the knob and bend it back and forth (on this one as well as on the mode select rotary), you can get it to select channels 9-16, but then you can't even breathe on it, or it will lose the connection.

Of all the things wrong with it, I think this is the most important to fix for me right now. Can someone tell me what might be the problem and how to fix it, please?

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rv0
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by rv0 »

replace it.

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

I can't replace it. You couldn't take the time to write more than that?

Anyway, the rest of the stuff, I can live with, and I already tuned it. I just want to make this selection knob less jumpy, and it'll be perfectly usable for my current purposes. I also didn't build it, like I mentioned, but I don't mind opening it and replacing some of the parts to A) fix the problem and B) get to know its inner workings more closely.

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mmm
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by mmm »

Obviously the switch loses the highest bit. If this is perhaps the result of a cold solder joint or of the switch itself is hard to say. If the solder pads look ok it's probably the switch itself; and then it needs to be replaced.
If the Mode switch is affected as well the problem lies elsewhere.

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

The Mode switch itself seems to work OK, but jiggling it can affect the other knob's willingness to read the higher bit, so maybe it's just affecting a loose connection on the 1-16 knob side?

Also to "darf fader," when you wrote, "replace it," I assumed at first that you meant the whole x0xb0x, hence my testiness. Maybe that is not what you meant, but that is the kind of communication problem you can run into when you give only an ambiguous, two-word reply. The problem is that I don't know what to replace! Schematics and pictures would be very helpful. I have never worked on a x0xb0x before, and I am not an electronics wiz per se, but I can solder.

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antto
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by antto »

yes, he meant "replace the rotary selector"

as for more info, here's the original BOM: http://www.ladyada.net/make/x0xb0x/fab/parts.html
scroll down to the "Mechanical parts" and you'll find it

try what MMM suggested first

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

Thanks, I'll give it a look.

BTW, your tuning VST was very helpful.

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

OK, so after experimenting with this x0x a while longer, I am noticing that the cutoff and volume knobs also exhibit similar behavior. The volume, for example, does not turn all the way off unless you set the knob to zero, then pull down on it. Cutoff does the same thing.

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antto
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by antto »

what does that mean exactly?
i suppose you're not confusing the direction where the knob cap is pointing against the tick marks on the panel, since the alignment can be a bit off there

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

No, the knob is pretty easy to figure out. Turn it counter-clockwise to lower the volume; turn it clockwise to raise the volume.

What I am saying is that when it is entirely counter-clockwise, the sound continues. Only if you then jiggle the knob by pulling down on it does it actually register the "sound off" setting. Same thing with "Cutoff": turn it all the way down, and you're not getting the lowest filter setting unless you jiggle it/pull on it...but pull on it hard enough, and the sound stops completely! Clearly a bunch of these knobs have loose connections of some kind.

PS - For the record, I bought this x0x in "excellent condition" from kappaguy99 on eBay.

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rv0
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by rv0 »

sounds like this x0x fell down on the pots, and either the pots itself are broken or the connection with the pcb is dodgy.. i'm guessing the first

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midiquestions
 
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Re: Dodgy MIDI Channel Selector Knobs

Post by midiquestions »

Do you think it was something the assembler did to them, or that they came that way? I am curious b/c it affects both the regular pots and the 1-16 selector knob.

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