These days a Mk.I String Ensemble made its way on my table.
While working perfectly without the ensemble effect, it showed some heavy noise and reduced volume in ensemble mode.
The noise turned out to be a defective TCA350Y BBD chip. While I’m waiting for the replacment part, I checked the other two delay circuits and found one showing no output at all. Fortunately only a transistor in the astable circuit driving the BBD’s clock inputs was intermittent, so all transistors of this type will now be replaced to prevent further trouble.
There were several types of this instruments available under different manufacturer labels – Solina, ARP and Eminent. The earlier models used TCA350Y BBDs while the latest had TDA1022s.
(for the case your String Ensemble is missing one or more certain notes…)
At least three different top octave synthesizer chips (TOS) were used: M087, SAA1030 and TMS3616. All of those could be replaced by my universal replacement module RPLTOS or RPLTOS+.
Read more about this little board here http://huebnerie.de/index.php?article_id=14 (in German language)