Casio PT-50 small keyboard with nice analogue rhythm, accompaniment & ROM-Pack

This was the only Casio keyboard with ROM-Pack slot but no key lighting; instead it can load the ROM-Pack musics into an internal sequencer, and with the optional Casio TA-1 module it can even save them on audio cassettes. Even a RAM-Pack cartridge Casio RA-1 was made for this thing to save sequencer data - I never saw any other Casio keyboard designed for using it.

Despite this keyboard looks almost like a twin of the Casio PT-30, there are many small differences. 3 of the 8 preset sounds are changed, the chords and bass timbre is different and also the rhythm set is completely different and includes fill-in. Even the LCD has different segments and shows e.g. a "J" for major chords. Also the sequencer of this thing was changed and is horribly awkward like with Casio MT-70, because it apparently neither can record note lengths in realtime nor melody and chord together, thus everything has to be entered in different modes step by step. But by the general similarities I only explain here the differences to the PT-30.

different main features:

  • 8 OBS preset sounds {piano, harpsichord, organ, violin, flute, clarinet, trumpet, celesta}.
  • 16 preset rhythms {rock, rock'n'roll, disco, 16 beat, samba, latin rock, bossa-nova, beguine, tango, march, waltz, rock waltz, slow rock, ballad, swing 2beat, swing 4beat} made of analogue percussion + bass & piano accompaniment (contains no arpeggio).
  • tempo +/- buttons (19 steps, counts 1..20)
  • different editable sequencer (no realtime recording, terribly awkward!)
  • transpose buttons (12 semitone steps)
  • different LCD display shows pressed keys and chords (only important for the sequencer)
  • ROM-/ RAM- Pack slot (but no key lighting/ melody guide feature)
  • demo button (plays musics from the inserted ROM-Pack when present)
  • multi-chip hardware:
    • CPU= "NEC D1868G 004, 8314EK, Japan" (80 pin SMD)
    • 2x SRAM= "HD  B, 61914, 3D, 23" (44 pin SMD)
serial F015914


eastereggs:

  • To mute only the accompaniment but keep the rhythm running, keep the sequencer memory empty and press the "one key chord" button.

modifications:

  • Power supply jack polarity changed and protection diode added.

notes:

Like the Casio MT-800, this instrument came with the ROM-Pack RO-201 and has to load ROM-Pack musics into its internal RAM (takes a few seconds) before it can play them. This is also valid for the demo melody, which doesn't play with ROM-Pack removed (shows error "E -") despite the melody keeps playing when the ROM-Pack is removed while the demo is playing. The hardware in the small PT-50 case is even more crowded than in the similar looking Casio PT-30, because between panel and analogue PCB it contains even a 3rd intermediate PCB for the digital ICs. But fortunately this daughter board at least makes the CPU behaviour a bit easier to examine since you don't need to take out the panel PCB (with a hand full of loose buttons flying around) to access it. Also the LCD here is held by a sheet metal bracket that didn't exist in the PT-30. (I haven't examined the hardware further yet.)
Some preset sounds differ from Casio PT-30: The "organ" here has neither vibrato nor sustain, the "violin" and "flute" here lack sustain also. The sounds "horn", "fantasy", "mellow" of the PT-30 were replaced with "clarinet" (has no vibrato), "trumpet" (like "horn" without sustain) and "celesta" (like "harpsichord" with sustain and 1 octave higher).The manual organ chord voice lacks the dull organ bass component and instead everything plays an octave lower, which sounds cheaper and more squarewave- like. In opposite to the PT-30, here you can trill around on different chord type buttons while holding a chord note key. (The PT-30 ignores further chord type button presses, thus you have to also release and press again the chord note key before you can choose another chord type, which was bad for comparing how different chords sound.) With rhythm, the bass voice has here a low, sonorously buzzing, decaying squarewave timbre with sustain, that reminds to an e-bass, but is also a little brassy. The rhythms set is very different from PT-30 and unfortunately lacks the nice arpeggio styles. But instead the rhythms now have each a fill-in pattern with accompaniment. Annoying is that the rhythms don't start immediately anymore after selecting them, but you have to press the "start/ fill-in" button, which always begins with a 4 step snare lead-in before starting the rhythm itself. Also the pattern restart trick of the PT-30 can not be used here by the lack of "chord change" buttons.

Casio RAM-Pack RA-1I finally found on eBay the mysterious RAM-Pack cartridge for the Casio PT-50. It is named Casio RA-1 and can store apparently only one song. You can even save any ROM-Pack song from the internal PT-50 sequencer memory to it, which is correctly loaded back including the obligato voice.
I first hoped that it would be possible to compose own musics on the PT-50 (or even PC through the TA-1 tape interface) and play them on other ROM-Pack compatible Casio keyboards. However unfortunately the RA-1 seems to be incompatible with normal ROM-Pack keyboards; they ignore it like when the ROM-Pack slot was left empty.
The RA-1 contains a 3V lithium button cell "BR-2016"; the manual claims it would last only 1 year, but longer with RA-1 inserted into the keyboard. (This can make only sense so far the keyboard contains batteries.) However in PC mainboards the same kind of "CMOS" memory backup batteries last about 10 years. For battery replacement you have to open the cartridge; first remove the slider, then unscrew the 2 tiny screws underneath.
To analyze the hardware closer, I needed to take out the PCB itself. But the only screw holding it was jammed in so tightly, that its flat soft iron head refused to be moved and only crumbled apart by any serious attempts of loosening it. Thus I had to drill it out; unfortunately the thin drill I used suddenly bent away by too much force, which made my heavy household drill machine violently crash down into the PCB, resulting in a PCB crack that damaged a lot of traces - arrg! Fortunately by my Casio KX-101 nightmare repairs I was more than experienced enough to patch them together again.
The hardware is made of 2 identical SRAM ICs "HD B 61914". Interesting is the pin assignment; the left side of the 1st RAM exactly corresponds to the pinout of the ROM-Pack slot, the traces are 1:1 connected with its top side pins and with the left side of the 2nd RAM. To top row pins of RAM 1 are all wired to +Vs. Almost all pins of the down side of both ICs are shorted with each other. To the right side only few pins are used (apparently for control purposes), while many others are shorted too. I assume that the top pin row of the 61914 IC is likely NC (internally not connected) and thus simply connected in a way that makes it easiest to route traces from other pins underneath it on the single sided PCB.
Casio used the same IC also as internal SRAM in the PT-50, the PT-30, and a similar looking HD C 61914 in the KX-101.
The ROM-Pack implementation of this keyboard is very different from all my other Casios and a little unobvious. To select a song, press the "R/MT" button once ("R" appears in the LCD), then type the 2 digit song number with the rightmost keys and press "play", which copies the song into the internal RAM (takes some seconds) and plays it. (Pressing "R/MT" twice displays "MT" and apparently tries to load the music file from a cassette through the optional Casio TA-1 module.) Unlike a ROM-Pack, the RAM-Pack RA-1 ignores the selected song number, because it apparently holds only 1 song. The "demonstration" button plays all musics from the inserted ROM-Pack in a sequence, starting with the first. The 2nd melody voice (obligato) of ROM-Pack musics plays a bit too quiet on my PT-50. (Warning: Playing any ROM-Pack musics overwrites and thus deletes the actual sequencer contents.)
Unfortunately I have no manual for this thing, but this is what I found out. Press "chord" and then "play" to play only the chord track. Press "melody" and then "play" to play only the main voice. To delete the sequencer contents hold "record" and press "clear". To record your own melody into the sequencer, hold "record" and press "melody" to enter melody recording mode. Play the melody note by note (press "reset" to quit). Afterwards the note lengths must be entered separately, and also chords can not be recorded together with the melody. :-[  (No joke! The PT-30had no trouble with that.) To enter the note lengths, press "play" in melody recording mode and step with the right tempo through the melody using the "one key play" buttons until the melody ends (or press "reset" to finish). When no note lengths are entered, the melody plays with tremendous speed. To record chords works similar, but hold "record" and press "chord" for the chord recording mode. To enter chord lengths (not necessary when you played right), press play in this mode and step forward with the "one key chord" button. To edit the sequencer contents, enter the melody or chord recording mode again and step through your track with the "for" button. Any new played notes or chords are inserted at the current position. The "delete" button deletes the last played note/ chord from the track. After edit press play in that recording mode and correct the note lengths with the "one key play" and "one key chord" buttons again. (Note: ROM-Pack musics contain beside melody and chord voice a 2nd main voice called "obligato"; unlike melody and chord, this additional voice can apparently not be edited in the sequencer.) To save the actual sequencer contents on a RAM-Pack, press "R/MT" once and then "save".

Like the Casio PT-30, the PT-50 has an expansion cartridge slot for the Casio TA-1 tape memory interface to save the sequencer contents, thus it might be possible to save with this thing ROM-Pack music data on cassettes or upload them to a PC for further analysis or even sound emulation. Unfortunately you can not play them through the RAM-Pack RA-1 on other ROM-Pack keyboards, because the RA-1 is incompatible with them.
 


Casio PT-20

(photo from eBay, showing my specimen)

This tiny instrument seems to be just a downsized Casio PT-30 and sounds very similar. (I haven't examined the hardware yet.) Unlike the latter it is missing the LCD, the cartridge slot, some of the sequencer buttons, the transpose buttons and 2 high note keys (thus also the "arp. 6" rhythm). Instead of separate rhythm and chord volume sliders it has only a combined slider. Its small case resembles the Casio PT-1. The original German retail price in a German Conrad catalogue from 1986 was 199DM (about 100€).

The likely most advanced member of this hardware family was the ultra- rare keyboard boombox Casio KX-101 (37 mini keys, chord button pad, complex sequencer that saves data on audio cassettes), which was even 4 note polyphonic.