Display noise (was K5000 warranty support)

[Haible Juergen]

>><< P.S. Anyone notice a real soft high pitch whine coming from the power
>> supply?  I hope this is common and not another problem with my unit... >>
>>
>>This is coming from the LCD display; same thing for Wavestations and A50s
and
>>A90s.
>
>This is REALLY common for backlit LCD's.
>We used to see a ton of units come back at Roland for this exact issue.
>
>Some display power supplies (DC-DC converter) whine louder than others.
>Possibly some resonant thing going on with their transformers or the
>display itself.
>
>There are things that can be done to minimize it, but I don't have any easy
>solution.


This can be very annoying indeed, and I remember how disapointed I was when
I sold my "virtual analogue" D-50 (quiet) and bought a D-550 (high pitched
noise) instead.
I checked with Roland, they faxed me a copy of the PSU page from the service
manual and told me that they have changed the display from the keyboard to
the expander version of the D-50.
The new display needed an external high AC supply voltage (might be around
100V, don't remember exactly), and this was generated by an oscillator and
a little transformer. High frequency, small transformer, law of physics, and
law of economics ...
I tried everything to get this transformer quiet, pieces of styrofoam,
various
types of glue, pieces of carpet, but I didn't get it quiet.
Then I decided to replace the whole crappy circuit. The display would run
on 50Hz AC as well, as long as the voltage was the same.

I tried a few cheap AC wallwarts, connecting them *backward* to one of the
D-550's main PSU transformer secondary (!!) windings, until I found one that
had approx. the right (100V) voltage at it's *input*, when its *output* was
fed
from inside the D-550. Of course I could have done the same thing with a
little
transformer, but I wanted the isolation of the wall wart to avoid problems
with
building it into the expander.
This "reverse wallwart" is inside my D-550 for years now, and I never had
problems
anymore. The display is a little darker than before, but I could have had it
brighter by selecting a different wallwart. BTW, trying and selecting is the
way to go, "reverse" calculation will lead to false results, because these
small
transformers have high losses, and these go into the calculation with
different
sign when connected forward or backward.

Disclaimer:
Don't do this mod without knowing exactly what you do - I guarantee for
nothing.

JH.