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xoxbox won't stay in tune. please help!! (Solved)
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xoxbox won't stay in tune. please help!! (Solved)

by juicepatrol on Wed Feb 24, 2016 3:06 am

I just recently got a used mode machines xox mk2 online. It didn't come with a power adapter. I ended up having a 9vac 780mA and it worked. The xoxbox is in good shape but when I got it it was out of tune width wise (tm5). I ended up poking around the forums and managed to get it perfectly in tune with tm4 and tm5. But every time I turn it off and come back later the scale is out of tune again and I have to redu the whole thing. Is it possible that since the power adapter I have is 780mA and not 500mA it is making it go out of tune. Any advice is appreciated this is driving me crazy.
Last edited by juicepatrol on Sun Feb 28, 2016 11:06 pm, edited 1 time in total.

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Re: xoxbox won't stay in tune. please help!!

by antto on Sun Feb 28, 2016 7:18 am

highly unlikely to be the adapter
the VCO has a thermo-sensitive resistor, it should compensate for temperature differences, but it may be not working, or not positioned properly, or wrong value.. who knows

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Re: xoxbox won't stay in tune. please help!!

by MMM on Sun Feb 28, 2016 1:23 pm

I need the serial# of the xoxbox; then I might be able to help you further.
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Re: xoxbox won't stay in tune. please help!!

by juicepatrol on Sun Feb 28, 2016 4:20 pm

The serial number is 00473. I have checked out the thermistor and it doesn't look like any other ones ive seen online. It is big and grey. When I measure it I get 560ohm.

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Re: xoxbox won't stay in tune. please help!!

by MMM on Sun Feb 28, 2016 5:02 pm

Where are you located?

The thermistor is wrong; there had been a number of machines from that series with this thermistor.
One of the technicians at Mode Machines at the time had the brilliant idea to use a different part when building this series; what he didn't notice was that he was substituting an NTC thermistor in place of a PTC. The thermistor has the function to counter the thermal effects; but using the wrong type means that it actually worsens the thermal problem and the xoxbox is never really fully in tune. This was especially ironic since I had implemented a different parts substitution a few months earlier that actually improved tuning precision; you can imagine how "happy" I was when those machines started showing up at my door...

Anyway, if you're in Europe Mode Machines will probably fix this at no charge. If you're outside Europe it's probably easier to take the machine to a tech to have it modified; I can supply the parts for this.
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Re: xoxbox won't stay in tune. please help!!

by juicepatrol on Sun Feb 28, 2016 5:32 pm

I'm actually in America. I bought the box off ebay from the UK. But I have already ordered the (2) ptc 1k thermistors from the wilzyxk site. So they should be here in the next couple of days. These should be fine right? I also wanted to know that if I needed to replace r106 with a 24k if I swap out the bad thermistor for the good ones? Thanks so much for your reply btw =)

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Re: xoxbox won't stay in tune. please help!!

by MMM on Sun Feb 28, 2016 6:08 pm

Yes, R106 should best be 24k when using the two thermistor setup. It's possible that your xoxbox has some kind of "kludge" out of two resistors in place of R106; I've seen this a couple of times with the affected units. Some also had already a 24k resistor installed. It is very clear that the tech at the time was really struggling to tune it somehow.
Usually when installing the correct thermistors (and exchanging R106 if needed) the xoxbox becomes very stable; and since those units use high-precision resistors for R74 to R90 you should be able to tune it very precisely. When I tune those boxes I aim for less than 5 cent deviation between the lowest and the highest note; and usually all the notes between also stay within 3 cent or so from the ideal tuning.
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Re: xoxbox won't stay in tune. please help!!

by juicepatrol on Sun Feb 28, 2016 11:04 pm

fantastic! Thank you so much that is a load off my mind. When i test r106 it is around 29k so it looks like i'm gonna have to order a 24k but at least I know what to do now.

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