Teisco SX-400 Calibration

[apprenticemart2]

Little bump.

OK. Nothing wrong with my scope after a 2 day strip down, just some poor connections on the odd cap.

No one with any experiences of the SX-400, more readable copy of the service manual maybe?

Cheers

Martin

[acreil]

Check that the battery's not leaking while you're in there. If it's the original NiCd battery, you may want to remove it.

[apprenticemart2]

I've already cleaned that mess up and it was a mess.
A previous owner managed to fry everything connected to the memory chips and beyond, some 14 chips. I just had to replace another chip this morning. It was leaky on one pin and the battery was discharging.

Hopefully I don't have any more problems on the CPU board. I installed a flash memory chip instead of the Eprom, and a lower power Z80 so hopefully that shaved a few 100 milliamps of the power supplies work.

I will just have to soldier on and calibrate it by ear.

Cheers.

[apprenticemart2]

Anyone know how I can fix the aftertouch sensor? It's not particularly sensitive any more.
Cheers
Martin

[apprenticemart2]

^
I was able to take the touch sensor strip apart and clean it with some isopropyl alcohol. It works great now.

[apprenticemart2]

The Teisco SX-400 has 1 CV/Gate in, that is sent to all 4 x voices so they are stacked.

I am trying to modify the CV circuit so that I can control each voice individually.(I think I already have an idea of how to provide the gate signal without too much of a problem)

I have re-drawn a section of the original schematic as best I can to show the CV-in section.

Is the op-amp section a buffer of some sort, or is it to beef up the input signal so that it can drive the 4 voices from 1 input?
(I'm guessing I may need to build another 3 of these)

Can I hack some inputs with switched jacks straight in between the outputs of the 4051 and the 820? resistors?

Yes, I know I could just start experimenting but I thought I would drink form the font of knowledge before I get stuck in an break something.

Any pointers would we greatly appreciated. It's very difficult to read the original schematics so I'm probably getting a lot wrong.

Thanks
Martin

[apprenticemart2]

The 4051 I'm guessing is used as a demultiplexer.
(After the 4051 there are some op-amps. I'm guessing they are working as sample and holds.)


Could I superimpose another 4051 on top of the one that is there, and use it in reverse as a multiplexer to send 4 cv inputs in on the Y and out of the common Z and clock it to the same signals that are on A B C? The Z of this 4051 would be connected to the Z on the 4051 in the SX-400.