I bought a new synthesizer on ebay two days ago, and it arrived today
(2017/11/16). I suspect it was made back in the 80's because it's circuit board
was layed out by hand (pretty, curved lines everywhere) and single-sided. It
has a four-position volume slider, 25 keyboard keys (10 black, 15 white), a
"vibrato" (makes the sound go up and down) switch, and four 28-note recording
tracks (don't know if that's what you call it, but they call it "tempo mode".
You can record and play back notes using a four-position selector switch, a
playback button and a clear button.) There are also 10 pre-programmed song
accessible by a button. 4 of them are christmas songs! I know it was made in the
eighties, but it's not even thanksgiving yet!

It can't play the tetris theme song Korobeiniki because the sampling rate is too
low. It only gets about 3/4 of the notes. Speaking of notes, you can only play
one at a time. If you try to press multiple keys, it picks the lower note. Most
synths of the time can only do one note, but it's usually the first note that
gets played, iirc. The included songs all play very slowly. 

It uses a M8316 LM386N-1 op-amp, a S+B8432 C0P420-HGZ/N controller board, a P8344 CD4069CN inverter that has something to do with the recording functionality,
two nice-looking taiwanese speakers, and a cheapo rubber-dome keyboard with a
matrix built in to the main board. The matrix is kinda sloppy, using 8x4 instead
of a 6x5 grid, and has about wight bridges instead of the four or so I expected.
The plastic case is nice and thicc, with a battery compartment for six batteries
even though it only uses four. It tried to warn me but the engris was
indecypherable. On a sticker inside the battery compartent, it said "TO INSTALL
SPARE BATTERIES." I've gotta give them credit for trying. The vibrating drums on
the speakers appear to be made of a thick cardstock. I don't know if that's
normal.

I plan to put a STM32F microcontroller in. It has 32K of storage/memory onboard
(1K of which is volatile), and a 32KHz clock speed. It only has THUMB
instructions, which are so few that I have them all memorized. Phlog post on
them soon. Since it has a keyboard and stuff already, it would be a cool thing
to redo into a nice computer. It already has speakers and a case.