Elektor Formant Modular

Hello everyone,
I have finally been able to continue building the (original) Formant 
VCOs again this summer.
These VCOs are build with original parts (uA726 and all), but with the 
updated Fet opamps (LF356H).

VCO #1 - everything works just fine!

VCO #2 - the core works (CCO, Exp conv., summing amp), and sawtooth and 
"spaced sawtooth" works fine.
However; the triangle (and hence the sinus) converter does not work as 
it should. It looks fine on the scope after the two diodes (the 
clipping part), but then something goes wrong, and all I get is a very 
weak (like 0.1V amplitude) semi-sawtooth. I have changed diodes, 
changed transitors, tripled-checked all components, solderjoints and 
connections. Putting in the optional cap (C13) does not change 
anything. It´s a fairly simple little circut, that triangle shaper, so 
there shouldn´t be much wrong. Any hints as to what I can do?

VCO #3 - the core does not work. Or start at all. Tomorrow I will try 
to put in the trimmer (P10) that was not needed because of the updated 
FET op-amp. It mentions in the text that inproper balance/level with 
the original FET transistors could lead to the VCO core not to start, 
hence the trimmer. However, this should be redundant with the new FET 
opamp. There could of course be something completely else that is 
wrong.
The summing amplifier for CVs (fine and course pots, offset trimmer, 
external CV etc.) seem to work.
The exponential converter seems to work.
All components gets the correct power (+15V, -15V, +5V, gnd)
I have used quality timer caps (polypropylene)
The transistor has been tested (I build the testing rig as explained in 
the book) to spec
Checked all components etc.

Any help appreciated.


Terje Winther
terje.winther@...
http://www.wintherstormer.no/