Patches and discussion for Ensoniq VFX family

On Fri, 2009-01-30 at 21:48 +0000, markbreton@... wrote:
> ok, that i will do.   i can't get a hold of the soniq, i have emailed
> and called to arrange to just send him the keyboard but have not heard
> back, and he doesn't have an answering machine.  interesting chap.  how
> do i check a diode?

Okay, you're going to either need to learn a bit about electronics, or
find someone to help you ;-)

On the power supply board there are sets of diodes arranged as a "bridge
rectifier" which is essentially a way of turning the AC power into a
rough approximation of DC, which is then smoothed by the capacitors and
regulated by the regulators.

There are a number of things that can go wrong.  From my own experience,
I've found that the rectifier diodes fail quite often on older synths,
usually short-circuit.  They're supposed to only pass current one way,
but when they blow they start to pass current *both* ways - not a good
state of affairs, and one that will definitely blow fuses in the VFX
power supply (the VFX and VFX-SD power supplies look the same.  They
might be the same as EPS ones too, I need to compare side-by-side.  My
VFX power supply has a floppy disk power connector).

Basically to test them, you need to remove them from the board (making
sure you know how they go back in), and check that they only pass
current one way.  If they don't pass any current either way, or pass
current both ways, they're stuffed and you need to replace all four (no
point just doing one - another will fail immediately when you put the
power back on, most of the time).  It's not hard, but you *will* need a
few specialised tools and a bit of skill with soldering.  Find your
friendly neighbourhood electronics geek and bring your synth round with
some beer or other socially acceptable bribe.

I usually replace the diodes in synth power supplies with ones rated at
10A at 800V.  They don't need to be that big, but it means they will
never ever fail again.

Gordon