[sdiy] x0x repair questions

ezion ezion67 at gmail.com
Mon Dec 23 07:46:53 CET 2013

I build about 13 x0xb0x'es so far.
Some where ordered with different LED than the standard red.
In those cases I had to change the resistors driving the LEDs as well.
This might be your problem also.

Cheers, Theo
Groetjes Theo

On Fri, Dec 20, 2013 at 7:25 AM, Pete Hartman <pete.hartman at gmail.com> wrote:
> These may be more generally applicable too....
> I picked up a non-functional x0xb0x for a good price, with the intent
> to repair and resell.
> The good news is, the repair is 99% done.  A number of interesting
> problems, but nothing too frustrating.
> I have one repair related question and one general question.  The
> repair-related one is: does anyone have a suggestion for a good way to
> match LED colors?  Particularly BLUE.  The 13 note LEDs are blue, but
> it's not the piercing bright blinding blue I'm accustomed to :-).
> Unfortunately, I don't have any stock of ANY 5mm blue LEDs, so I will
> have to source some.  I'd ask the builder, except apparently this
> board has been through several hands before it came to me, so I don't
> know who that is even....and that was a couple years ago, so I think
> it's fairly unlikely they'd even remember if I did track them down.
> The ground plane in this beast is pretty hard to work with when
> desoldering, even with my temp controlled iron, so I really don't
> relish the idea of replacing all 13 LEDs....
> The general question is: one of the problems was a significant
> low-frequency (100Hz?) hum on the output.  It did not vary with the
> volume setting, was about 1Vpp, and was a periodic but irregular
> waveform.  Kind of like a folded sine with some resonance added.  But
> the sound to my ears was just a barely buzzy low hum.  It did not show
> up on the "mix out" jack, only the headphone jack.
> As I tracked this down I found three classes of problems.  1) the 5V
> regulator had been bent back and forth and was barely attached, so
> bumping it reset the x0x.  2) the 6V regulator was putting out 12V
> (this feeds power for the headphone amp only)  3) there were a
> significant number of what appeared to me to be cold solders in the
> vicinity.  I repaired all these things and the hum is now gone.
> I'm curious what my culprit was likely to be for the hum.  My
> immediate reaction was that the 5V regulator was unlikely, it was just
> causing overall instability because it would reset the processor and
> doesn't directly feed the output.  I figured it was the 12V instead of
> 6V supply for the headphone amp, but as I think about it I'm not sure
> that it wasn't possibly the cold solders.  Anyone with more experience
> care to hazard a likely guess? If it was the 12V supply for the
> headphone amp, I'm curious why that might be.
> Thanks!
> Pete
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