eml synthesizers

My EML 200 is doing something strange. First off, OSC 2 is not
working. BUT if I turn up the Frequency knob all the way, poof - the
fuse is blown. Any ideas?

> My EML 200 is doing something strange. First off, OSC 2 is not
> working. BUT if I turn up the Frequency knob all the way, poof - the
> fuse is blown. Any ideas?

If the wiper of the frequency pot is shorted to ground (or maybe
to the case?), it would short out the power supply when you
turned the pot to max. Check that the wiper (middle connection)
of thepot isn't touching anything else, check that the wire
from the wiper contact hasn't come off at the other end. There
is an electrolytic cap between the wiper and ground - if that
has gone short, that might do it.

I'm just working from the schematic. I don't own a 200. Got any
photos of the inside.


Steve

Wow Steve,

Good call. I checked the pot and there was a spot that was questionable in touching the
faceplate. Cleaned it up and it's working great. NOW seeing as you are that good with
schematics, any idea why the Both Saws and Square wave will not work on OSC 1 of my
EML 101? (Triangle and pulse work) ;)

Thanks again Steve,
Heath

--- In emlsynth@yahoogroups.com, Steve Ridley <spr@...> wrote:
>
>
>
>
> > My EML 200 is doing something strange. First off, OSC 2 is not
> > working. BUT if I turn up the Frequency knob all the way, poof - the
> > fuse is blown. Any ideas?
>
> If the wiper of the frequency pot is shorted to ground (or maybe
> to the case?), it would short out the power supply when you
> turned the pot to max. Check that the wiper (middle connection)
> of thepot isn't touching anything else, check that the wire
> from the wiper contact hasn't come off at the other end. There
> is an electrolytic cap between the wiper and ground - if that
> has gone short, that might do it.
>
> I'm just working from the schematic. I don't own a 200. Got any
> photos of the inside.
>
>
> Steve
>

> Good call. I checked the pot and there was a spot that was questionable in touching the
> faceplate. Cleaned it up and it's working great.

Splendid!

> NOW seeing as you are that good with schematics, any idea why the Both Saws
> and Square wave will not work on OSC 1 of my EML 101? (Triangle and pulse work) ;)

If you look at the schematics for the 101, page 6 has VCO1. The squarewave output
circuit is in the top right of the page. It goes to the sawtooth wave reset circuit,
so if the square wave is dead, you get no sawteeth either. I assume the squarewave
also goes to the waveform selector switch, but it's not shown on the schematic.

The triangle is OK coming out of the 748 opamp, so it's either the block marked "S.T."
(presumably schmitt trigger - a squaring up circuit), the transistor buffer (the bit
with the circle drawn around it) or the wiring.

I've never been inside a 101, so I can't take you very far. Also, I don't know your
level of electronic ability, so let's start with the easy stuff.

Unplug the juice and trace the wire from the square position on the VCO1 waveform
switch back to board 2. I'm guessing there should be two wires off the square
output of the board - one to the switch and one linking to the sawtooth reset
circuit. Check that they haven't broken off. Also check that neither wire are
shorted to ground, especially at the switch.

If they're OK, the next most probably cause is the two transistors with the
circle drawn around them. That circle implies that someone has had a problem
here before, and it's not a well protected circuit. If you don't know how
to check the transistors, then it's a job for a tech.

If the two transistors are OK, then the last place to check is the "S.T.".
I'd guess that the circuit is going to be the same as the one shown on the
VCO2 schematic on page 7. Again, unless you have some electronics
knowledge, it's a job for a tech, but if you feel brave you could check
under the board for dry (cold) joints or broken tracks - but try not to
snap any wires off the board.

That's all the help I can offer...


Steve