Casio PT-82
PT-87
EP-20		 small keyboard with ROM-Pack, key lighting & blip rhythm

Casio PT-82

This keyboard from 1986 has many similarities with the Casio VL-Tone 1 and PT-1, but includes a "melody guide" key lighting feature for music teaching (not the keys itself light up but a row of small LEDs above them) with ROM-Pack music cartridge slot. Unfortunately it is very restricted and lacks the built-in synthesizer, sequencer and 3 octave switch of the VL-Tone.

Although the automatic music playback from the ROM-Pack includes wonderful polyphonic accompaniments, the player can play own musics only monophonic with thin and dull sounding blip rhythms. A bit unusual is that this white keyboard has brightly coloured orange and red buttons and red lines while Casio normally preferred pastel colours. Also a red case version of the PT-82 was made (which according to an e-mail lacks the headphone jack). In 1987 it was re-released in grey as Casio PT-87.

warning: IMO this is the perhaps most boring sounding Casio keyboard with rhythm, so do not pay moon prices for this! - and no, it is not analogue. Even circuit-bent the behaviour stays stubborn and you can not play chords or accompaniment nor modify the digital sound synthesis (there are no eastereggs).

main features:

modifications:

notes:

The PT-82 was likely intended as a technically simplified successor of the Casio PT-80. The speaker has an unpleasant, loud mid- range resonance. The main voice sounds are the same like with the PT-80, but tend to sound a little thinner and harsher. These sounds resemble much a Casio VL-Tone 1; unfortunately they don't include the famous "fantasy" sound of the latter. Although the musics from ROM- Packs play with nicely orchestrated accompaniment, the player can play own musics only monophonic with a simple rhythm and no accompaniment at all. The distorted percussion sounds a bit harsh, very colourless, and really thin and boring (like when blip drums from a PT-30 keyboard would have been resampled at an extremely low resolution and sample rate which removes all dynamics). The rhythm patterns resemble PT-80, but are not identical (e.g. blip instead of popping base drum). Much like with VL-Tone 1, the harpsichord sound suffers from a too slow attack rate, which makes it unrealistic. In the plastic case of my PT-82 was an embossed mark that seems to be the manufacturing date 86-02-08.

When the instrument is switched on, it plays a tone scale (8 notes) while a light runs from left to right on the LED chain. The instrument was sold with the Casio ROM- Pack RO-551. The ROM- Pack cartridge employs the same conductive carbonized silicone rubber connector that is used in many LCD watch displays. (I had to clean mine and the contact row on the PCB with isopropanol to make it function reliable.)

More interesting is that the musics from it can be used with "melody guide" training feature, in which a flashing LED (next key) and a lit LED (current key) in the LED chain above the keys teach monophonic keyboard play. It has 4 training levels {1= with light, waits for correct key, 2= with light, no waiting, 3= without light, waits for correct key, 4= without light, no waiting}. After finishing a piece of music, the player can press the "rating" button to see how good he has played. To show this, a sort-of "wheel of fortune" noise effect is played while a light runs multiple times from left to right above the keys. The light turns slower and then stops at a certain key. The better the player has played (less wrong noted and timing flaws), the further right it stops with a short jingle that depending on how good the player was {"* TRY AGAIN"= falling notes, "** FAIR"= very disharmonic clip of "Unterlanders Heimweh", "*** GOOD"= fanfare, "**** EXCELLENT"= different fanfare}. As a sound effect, the rating jingles can be also started by pressing the "rating" button while the mode switch is set to "play" instead of "melody guide". In this case the melody guide level select switch selects which of the 4 jingles is played.
 

hardware details

The Casio PT-82 is based on the single-chip CPU "Hitachi HD61703B01".
The PT-82 was the cheapest and most primitive keyboard with ROM-Pack port. Its hardware is much simpler than PT-80 and contains far less analogue components. The CPU name strongly suggests that it is based on Casio MT-18 (i.e. late PT-80 hardware) with only changed software. The PT-82 instrument concept with rating algorithm is described in the US patent 4694723.

In my 1st PT-82 one of the red key lighting LEDs was faulty and had to be replaced. 

multipulse squarewave & timbre filter

The digital part of the sound generator is almost identical with Casio PT-80 (see there), but the analogue part was strongly simplified and hence sounds poor. The envelope height differs among sounds to match the volume (and shorten certain sounds?). They have maximum 12 steps (only 8 in 'violin'?) and thus plenty of zipper noise (unlike VL-1 without smoothening circuit). The main voice is routed through a fixed timbre filter, which is controlled by 2 CPU outputs 67 O5 (highpass) and 68 O4, those however stay always the inverted of each other (likely to save cost of an external inverter), so it has only 2 settings.
 
preset sound:
 multipulse pattern
filter O4
filter O5
piano 1111100000000000
H
 
harpsichord = piano
 
H
organ 1110101011001010
H
  
violin 11111110
 
H
flute 11110000
H
 
clarinet 1111011100001000
H
 
trumpet 1000000000000000
H
 
celesta = flute
 
H

The accompaniment bass voice is plain 1:1 squarewave that is alternatingly output with the chord and muffled by a capacitor.

The percussion has grainy digital envelopes (likely 3-bit) and thus is typical blip percussion. The snare looks like plain squarewave modulated (logic AND) with shift register noise. Unlike earlier models, this percussion is not routed through an external analogue smoothening circuit (nor there are trigger pulses to e.g. bypass the snare for this) but comes completely premixed out of CPU pin 74.

keyboard matrix

See Casio EP-20.

Casio PT-87

This grey cased instrument was a re- release of the PT-82 from 1987. Inside the case embossed marks for 87 and {5, 6, 7, 8} make me conclude that it was manufactured between may and august in 1987. Unlike the PT-82, it has the classical pale coloured Casio buttons again.
(old eBay photo of my PT-87 & PT-82)
The PCB of this specimen contains less discrete components, the shielding aluminium cardboard inlay is gone and the PT-87 has also no headphone jack anymore. The CPU is "HD61703B01, 7D 33". My specimen has a strange defect; when operated with batteries, it sounds distorted and howls, while with a power supply it sounds perfect. Apparently the battery voltage (5 batteries = 7.5V) is too low to operate the circuit properly - possibly a defective voltage regulator drops too much voltage.

Casio EP-20 'Muppets'

Also this yellow toy keyboard from 1987 (embossed case date and "© ha! 1987" under Muppets "Ms. Piggy" picture) is a mutilated Casio PT-82. The power supply jack, tuning knob, "rating" button and "melody guide" level switch are omitted (level stays always 1). Also the ROM cartridge slot is gone, instead it has only a fixed soldered ROM chip "OKI MS268V-57, 7405" which contains 4 nicely orchestrated musics from the "Muppets" TV series. The CPU is "HD61703B01, 7D 33".

eastereggs:

modifications:

notes:

I initially had analyzed this (rather boring sounding) hardware in the hope to find out more about the much more delicate and complicated PT-30 and PT-50 (same hardware family, flimsy foil cables) those are very unpleasant and risky to work with. But later I analyzed them too.
 

circuit bending details

The Casio EP-20 (Muppets keyboard) is a variant of PT-82/87. But instead of its ROM-Pack port, in EP-20 the CPU is wired to a ROM chip "OKI MS268V-57, 7405" (44 pin square SMD) that is nothing else than an internal ROM-Pack with 'Muppets' songs. An interesting technical detail is that it apparently technically contains 7 pieces of music, but the musics 2, 4 and 6 are empty files to make the ROM use only the white keys for song selection.
At the CPU the unused upper pin row is unsoldered to save space for making traces run underneath. There are 2 adjacent unused solder pads to CPU pin 9 and 21 those look like a jumper or omitted capacitor. But bridging them only makes the CPU keep resetting (power led flashes) or (with capacitor) not start at all. Because similar PT-series keyboards (e.g. PT-30 or PT-80) have a set of additional buttons to the left of the keyboard to play chords, I searched for such keyboard matrix eastereggs but found none; even the matrix layout has nothing common with PT-80, thus I think they use totally different software. Likely Casio had to rewrite everything to make the melody guide "rating" algorithm fit.

keyboard matrix

The keyboard matrix is grouped by 6 and relatively clean. That is to say, unlike e.g. PT-80 there is no chord button section supported by this CPU, so pins KO8 and KO9 stay simply unused. And like with other software numbers of this CPU, the matrix layout is unique and not just a variant of others with some places left blank. I analyzed the matrix by myself and later got a PT-82 service manual (that differed in octave numbering) to confirm.

Useful eastereggs in EP-20 are only those of PT-82.
 
2 KI1
3 KI2
4 KI3
5 KI4
6 KI5
7 KI6
8 KI7
9 KI8
 
CPU pin
in 1
in 2
in 3
in 4
in 5
in 6
in 7
in 8
in / out
 
o
F#3
o
C4
o
F#4
o
C5
o
F#5
o
C6
O.
piano
O.
flute
out 1
10 KO1
o
G3
o
C#4
o
G4
o
C#5
o
G5
o
F3
O.
harpsichord
O.
clarinet
out 2
11 KO2
o
G#3
o
D4
o
G#4
o
D5
o
G#5
rating
O.
organ
O.
trumpet
out 3
12 KO3
o
A3
o
D#4
o
A4
o
D#5
o
A5
rhythm
select
O.
violin
O.
celesta
out 4
13 KO4
o
A#3
o
E4
o
A#4
o
E5
o
A#5
-
(?)
tempo
-
tempo
+
out 5
14 KO5
o
B3
o
F4
o
B4
o
F5
o
B5
one key
1
one key
2
stop
out 6
16 KO6
-
(?)
o
F#4
-
(?)
o
F#5
 -
one key
1
one key
2
stop
out 7
15 KO7
-
-
-
-
G.
1
G.
2
G.
3
G.
4
out 8
19 KO10
-
-
-
-
M.
play
M.
auto play
M.
guide (halt)
M.
guide
out 9
20 KO11

The input lines are active-high, i.e. react on +Vs. Any functions can be triggered by a non- locking switch in series to a diode from one "out" to one "in" pin. The key leds are multiplexed from the matrix output pins {10..20} to pin {69..71} through 11 transistors.
 

legend:
"o"
 = keyboard key
O.
 = preset sound ('orchestra')
M.
 = 'mode' switch
G.
 = 'guide' switch
orange
background 		 = easteregg (unconnected feature)
grey
background		 = unconnected doublet

  • rating
    Solder a button with diode in series from CPU pin 12 to pin 7 to enable rating.
  • guide switch
    In the lower left(?) PCB corner (component side view, speaker facing left) between leds PCB and keys are 2 groups of 3 diodes followed by 1 diode. This fixed matrix diode CPU pin 19 -> pin 6 simulates a 'guide' switch set to "1". Desolder this diode at pin 6 (stripe end). Instead connect either its now open end through a 4 step switch to CPU pins {6..9}, or connect 4 button switches through each a diode from pin 19 to pins {6..9}.
    With the fixed diode removed (and all switches open), the guide mode defaults to 3, melody waits in a loop but leds stay dark and only light up when you missed a note for some seconds.
Among the 'mode' switch matrix places is a  'guide' doublet (diode at CPU pin 20->8) that behaves like the regular one but makes the CPU halt (key led 1 stays lit, sounding tones except percussion hang with stopped envelope) so long the contact stays closed. This may be a test feature to stop the program. Connecting a diode at 14-> 7 prevents panel buttons from working and does nothing else. A diode at 15->2 or 15->4 behaves like a mute note key, i.e. it does not sound but truncates any held note; like with regular keys, pressing a 2nd key will sound as usual.

ROM-Pack hack

In my 2nd EP-20 specimen I removed the music rom with an SMD hot air soldering station to transplant the 'World Songs' rom from a RO-551 and vice versa and though play the Muppets music on other keyboards. Important is to use a ROM-Pack with square 44 pin IC  "OKI MS5268". I used a RO-551 with JASRAC label and rough flat back (Japanese version?, apparently came with my PT-80). Other RO-551 (no JASRAC, shiny back with 3 holes) contain a rectangular 22 pin IC "Matsushita MN6404xxxx" that won't fit.
Theoretically to the EP-20 also a ROM-Pack slot can be added, but this would be mechanically very difficult and not worth the effort.
 
 removal of these screws voids warranty...    
WarrantyVoid
back to tablehooters collection
  
 
back