The SX 400 was made under the name Teisco from the year 1980 to1982.
It is a four voice programmabel (8 Preset and 8 Userprogamms) polysynth with CV and Gate.
The oscillators have sine ,saw and rectangle (PW and PWM) waveforms and a suboscillator.
They are switchabel as a dualvoice, a fourvoice or a monovoice.
In monomode you can give each of the four oscillators a diffrent range and finetuning (16´ 8´ 4´ 2´).
The filter has 24 dB and resonance with selfoscillation. Modulation is possible by LFO 1 or 2 and
+ and - ADSR. Behind the VCA is still a HPF and a ensemble. The ADSR can trigger by LFO 2.
The keyboard is pressure sensitive with diffrent routings, portamento and glissando is also available.
Press pictures for close-ups
Inside Keyboard CPU board PSU board
VCO board Mod board
Please check the condition of the backup battery.
The SX-400 is vulnerable to leakage from the NiCad memory backup battery located on the CPU board.
On trhe below[picture, the standard NiCad battery has been replaced
with a non-rechargeable
Lithium battery fitted in a holder.
When you decide to do this, you MUST remove the diode that allows charging. (clearly marked in picture)
Press picture for close-ups
Here's a binary dump of the EPROM contents.
It's proberly labeled "1P002".
A full color copy of the complete manual in one pdf file. 28 pages, 5,09MB. User Manual
Synthdoctor has made the complete service manual available. If your synth needs a repair,
He is specialized in repairing old/new synths, etc.http://www.synthdoctor.nl
Download the service manual
And here's only the CPU board section of the servicemanual. 3 pages. 3,1MB. CPU board
Huge article/review of the SX400 and other Teisco synths
Big thanks to Stephen Lenham, Ingo Rippstein and Martijn aka Synthusiast.