[sdiy] Cheetah MS800 Internals pictures
rburnett at richieburnett.co.uk
Sat Jun 5 18:37:27 CEST 2021
A few photos for your viewing pleasure:
The main ICs...
Main CPU: UMC 6502A
Wavetable Synth: SGS M114S
MIDI UART: 6850
MIDI Opto: PC900V
8KByte SRAM: 8464A-10L
2KByte SRAM: HM6116LP-2
CPU's ROM: M2764A
Wave ROM: 27C256
...and lots of address decoders and other glue-logic. 4MHz crystal running
the show. TL072 presumably buffering the audio output. And a trusty L78S05
regulator keeping one side of the case nice and warm!
The 8464A "Low Power SRAM" and the 74HC00 next to it are powered from the
battery backup supply.
When I take the main board out to change the battery, I'll stick it on the
scanner and get a picture of the bottom side tracking too.
Incidentally the SGS wavetable chip runs quite warm to the touch! It also
uses some sort of pulse-amplitude-modulation to output multiple voices to
the limited (2) audio outputs. There's little attempt made to filter this
at all, and the multiplexing is clearly visible in the waveforms from the
output jacks. Aliasing / Imaging is something this synth does in spades!
M114S wavetable chip datasheet:
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