[sdiy] Tiracon 6V - Vermona / VEB Cottbus - Help and Schematics Needed

[cheater cheater]

Hi guys,

I am trying to resurrect this Tiracon 6V that I got off eBay some time
ago. It doesn't put out any sound.

It came to me in a non-functioning state. Since then I have repaired
the PSU (hopefully correctly) and have been trying to work out why it
doesn't work, and how it works in the first place.

I have tried contacting Vermona about the synthesizer, however have
had no luck with getting a reply about schematics etc.

Currently, the digital board with the LCD turns on, and I can load and
edit patches (haven't tried to save them yet, not sure if that's such
a good idea). I can also change the speed of LFOs which is depicted on
the LEDs pulsating quicker or slower. There is no sound coming out of
the synthesizer.

It does seem that the scanning matrix works to some extent, since the
voices do seem to get triggered.

About the synthesizer layout: if you look at the pictures here:

http://www.vermona.de/htm/tiracon2.htm

then you'll see the arrangement of the boards is as follows:
the top of the synthesizer opens and has the LCD board in it. When
that's open, we are presented with several boards. From left to right:

1. leftmost: digital board - http://www.vermona.de/Tiracon/digitalteil.jpg
2. main/analog board with six voice cards -
http://www.vermona.de/Tiracon/analogteil.jpg
3. regulator board
4. rightmost: transformer board

(both PSU boards can be seen here: http://www.vermona.de/Tiracon/netzteil.jpg )

The voice cards themselves have a 2mm pin interface of some sort that
they plug into. I have been trying to scope them out.

About the PSU repair: the top left regulator (B3170V, an LM317 clone
from the GDR) was not in circuit and one of the capacitors has broken
loose. After soldering it all back together, I have had +15V show up
on one of the pins, where it was 0V before.

About the voice cards:
Pictures can be seen here:
http://www.vermona.de/instrumente/tir3.jpg
http://www.vermona.de/Tiracon/6-voices.jpg

they have two connectors, call them the Left and Right connector. The
Left connector has 12 pins, the Right connector has 6 pins plus a "key
pin" which doesn't do anything.

Here are my notes for the connectors:
Left:
1. frequency CV, V/Hz
2. 15V
3. GND
4. -15V
5. ?
6. 3.69V with a lot of digital noise
7. digital gnd?
8. digital gnd again?
9. ?
10. 5.2V
11. unused
12. -12V with a lot of noise

Right:
1. ?
2. very very quiet white noise. Perhaps the output pin?
3. ?
4. white noise, probably an input from central distribution.
5. gate. off = -7.29V, on= -7.53V
6. -13.23V

About the Left connector signals:
The Frequency CV is very weird. C3 is -0,470V, whereas C2 is -0.233V
and C4 is -0.945V. Obviously has a scaling problem, which I hadn't
tried to address yet, since that's like waxing a train wreck. The
weird thing is that the voltages are all negative.

Pin 6 in reference to pin 7 still has the digital noise, but the
amplitude is reduced by 50%. Pin 5 seems to contain a very very quiet
mix of the output, I might be wrong though. Or maybe it's just some
current escaping through ground to somewhere, who knows.


About the cards:

I have been able to get the 6V to run to some extent: the voice boards
receive triggers and they change in pitch according to the note being
played. The oscillator is audibly changing pitch if you listen to it
by tapping the voltage on either of its terminals directly (which is
funny, because I had thought only one of the terminals would have
output, but both do - one of them is much quieter though). I have had
a look around the board as to what it has got and it basically has two
areas. On the left there is the VCO and on the right there is the
filter.

One weird thing is that there is a droop in the oscillator's pitch as
long as the key is being held down. That means, that I will press the
key (repeatedly until the voice I'm scoping gets triggered), and the
pitch will change to what it should be minus a few semitones. Then
when I let go of the key the pitch jumps up.

The Gate is VERY weird. you can see the voltages above - off is
-7.29V, on is -7.53V. Definitely something wrong going on there.

The VCO area contains resistors, some small capacitors, some other
stuff which I am unable to identify, and these chips:
V 4 082 (probably a TL082 clone)
B084D V7 (probably a TL084 clone)
V 4066 D (a CD4066 clone, a quad bilateral switch)
a second 4066
CD4013 BE (probably the only western chip in the whole voice board).

The presence of two quad bilateral switches and the fact that the VCO
wave is audible on both ends of the capacitor (which is 15nF) suggests
to me that it is a triangular core vco. I assume that the second
switch is used for creating a sawtooth wave. I'm assuming the CD4013
is used as the comparator in the reset circuit (it is a CMOS dual
D-type flip flop).

The filter board is about the right 45% width of the board, and it
contains four chips marked as IA317D UD, some resistors, and some
small foil capacitors as well as tantalums. The chips appear to be
also known as AK317DC. Here's a thread about it in Polish:

http://www.elektroda.pl/rtvforum/topic755331.html

(google translate might help)

For example it was used in some old laser printers to control motors.
In the thread it is mentioned that it is an OTA. The presence of four
OTAs implies to me that it is a COTA filter, which fits together with
what I remember about the demos.

One good thing about this situation is that I have multiple sets of
boards for this synth: I have got the one keyboard, and I have got two
pretty much complete sets of boards as bare parts. Of course, none of
them work.

Any clues, guys?

Please help!

Damian