eml synthesizers

I posted here a little while ago about this, but I have since figured out more of what it's doing
wrong.

Long story short is that the Saw, Negative Saw and Square wave do not work as they should.
The triangle and pulse work fine. The three waveforms do not work in either LFO mode or in
audio mode.

Now the really strange thing is if I have OSC 1 controlling OSC 2 as an LFO what happens is if
I have lets say SAW selected and I switch it from high to LFO mode is will ramp up once and
just give me a high pitched sound once ramped up. Basically, it doesn't start a cycle again.
Same with NEG SAW. If I switch if from high to LFO it just ramps down to really low tone but
does not repeat it's cycle. Any idea what the culprit could be? My initial guess is a capacitor.

I can tell from the schematics that there is a section where the saws and square seem to be
off on their own which would explain why the three don't work, but the other two do.

There are clearer schematics and service manual here:

http://manuals.fdiskc.com/tree/EML/

There doesn't seem to be an Osc. 1 circuit, but parts of osc. 2 & 3
are similar, so look at the schematics on page 4 of the new redrawn
schematics.

> Now the really strange thing is if I have OSC 1 controlling OSC 2 as an LFO what happens is if
> I have lets say SAW selected and I switch it from high to LFO mode is will ramp up once and
> just give me a high pitched sound once ramped up. Basically, it doesn't start a cycle again.
> Same with NEG SAW. If I switch if from high to LFO it just ramps down to really low tone but
> does not repeat it's cycle. Any idea what the culprit could be? My initial guess is a capacitor.

If you read my reply from back when, you'll see that this all makes sense.

The square is derived from the triangle wave in the schmitt trigger circuit -
three transistors, a zener diode and a few resistors - it's labelled on the
schematic.

The squarewave is used to flip the ramp/sawtooth waves using a E112 fet (middle
top), so with no squarewave, the ramps will just rise and sit there waiting.
Which seems to what's happening. (The osc. 1 circuit is slightly different
here, but the basic idea is the same).

There is good news. The triangle wave also gets reset by the squarewave,
via another E112 fet bottom left, so the squarewave seems to be working.

If you look at the old schematics, they show the wire to the sawtooth circuit
coming off AFTER the two big transistors, like the wire to the waveform switch,
so I think your problem is either around the these output transistors (the
MPSA14 and MPSA66 on the bottom right of the new schematic). It could be one
of these has blown, or the wires to the waveform switch and sawtooth circuit
have fallen off.

I'd check for wires fallen off first, as that should fairly easy to see. Give
a GENTLE tug to make sure they're not just resting in the right place. Or it
could be a dry/cold joint. Inspect the soldering.

If a transistor has died, you may need professional help. I don't know the
extent of your ability.

All the above advice is from schematics. I don't have an EML101, so I'm
working from schematics only. There may be errors, variations or
transistor substitutions.


Good luck


Steve