[sdiy] Memorymoog acting strange

[Chris Manders]

Hi Christian

I don't know the Memorymoog, but the problem sounds
very similar to the one I had with my Moog Source. It
suffered from the 'Crazy Source' problem which was
caused by oxidisation on the voltage regulators which
are pushed into sockets on the circuit board.

I removed the sockets and soldered the regulators
directly down and the problem disappeared.

If not this, perhaps another loose connection
somewhere. 

Christian


--- ChristianH <chris at chrismusic.de> wrote:

> well, I know, they're almost all acting very
> strange...
> 
> Mine has developped something weird: it contiuously
> sees pot movements,
> even when completely left alone. 
> This is pretty nasty, since this will abort any
> calibration menu,
> and the display will jump to the changed pot values
> instead. Most of the
> time, I won't even get to the calibration menu at
> all, because I can't
> complete the "C" and number button sequences without
> being struck by
> some intervening pot change display.
> 
> At first I suspected the 4051s on the panel boards
> collecting the pot
> voltages, but replacing those didn't change a thing.
> Same with the 393
> comparator on the DMUX board. 
> 10 V pot reference voltage is perfectly stable
> within +/- 1 mV, both at
> the DAC and after the buffer for pot supply.
> 
> The programmable threshold circuits on the DMUX
> board (IMHO not quite
> correctly described as "hysteresis" in the technical
> manual, real
> hysteresis is only achieved in conjunction with
> software operation)
> appear to do their thing. If I manually activate
> them one by one, the
> MUX BUS voltage is increased or decreased by some 50
> mV, as intended.
> 
> If I completely remove the MUX BUS line, leaving the
> CR2/CR3 junction
> before the 393 comparator open, there are no changes
> seen. 
> However, connecting the bus line to a single pot or
> ground will show
> continuous movement again (and that pretty much
> precludes the simplest
> cause, i.e. a shaky pot).
> 
> Has anybody else ever seen behaviour like this?
> 
> regards
> Christian
> 
> BTW, I can't remember having seen so much bad
> mechanical engineering in
> one device (well, apart from my own wild'n'careless
> diy stuff I did at
> the tender age of 16). The wiring is a mess, oodles
> of cables going from
> everywhere to everywhere. Accessing the DMUX board
> (or even removing it...)
> is a major pain in the you-know-where. Big fat
> ground wires soldered
> closely in between two ICs only 100 mil apart, so
> you can hardly
> unsolder them without burning the IC sockets. Add to
> that lousy board
> silk screening where you mostly can't tell "6" from
> "8". Yuck.
> 
> If only that goddam thing wouldn't have that
> gorgeous sound ;-)
> 
> 


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