PT-31 - won't power on.. Where to start?

[534N]

@CYBERYOGI =CO=Windler- I haven’t seen any other parts that look corroded or anything. Since the broken parts are both in places where someone could stick something inside and stab around blindly, I want to say they probably got damaged from negligent abuse.

 

The rest of the insides look nice (as far as I can tell) and there’s only a little bit of dust here and there.. mostly just from the disintegrated foam.

 

Do you have any recommendation for dealing with the missing reset button? It’s just a piece of metal on a spring that bridges 2 contact points, right? So.. that function could be achieved by just using a flathead screwdriver tip, right?

 

I think I may just bring this thing to an electronics repair guy locally and see if a more experienced person can get to the bottom of it.

 

The LCD screen and it’s cable seemed to be in pretty good shape as far as I can tell. Nothing seems to be falling apart and I haven’t found any obvious corrosion outside of the battery compartment. Hmm..

[534N]

@CYBERYOGI =CO=Windler - Oh, side note: I know the PT-30/31 aren't related at all to the MT-65 .. I was hoping the chipset from the latter type of model might be available in a PT-sized model, but from a little bit of research, it looks like the answer is No, it's not. There isn't a smaller keyboard that uses that chipset. Too bad.. I think the drums and all the possible unlocked features from the MT-65 would be amazing in a smaller form. I love the feel of the tiny keys and the portability, as I mentioned before. Oh well..

 

The MT-52 looks especially interesting with the Super Drums feature. I would love to have that functionality on top of the MT-65 stuff. I'm wondering if those MT-52 features can be unlocked on the MT-65/68. That could be really interesting.

 

The thing that attracts me the most to the PT-30/31 is having all the little chord options on the side with tiny buttons and the sequencer. The transpose option is a great addition too. I want to add that functionality and form factor to the sound quality of the drums and voices of the MT-65. I don't think my dream keyboard exists so I will have to accept the limitations of each model and appreciate them for what they are. Limitations are actually great for creativity in my opinion.

[pianokeyjoe]

@534Non the subject of the MT65, you know there is a full sized version called 405. Casiotone 405. THAT would be the unit to tinker with. Now since you will now have BOTH the MT65 and the MT68, I would tinker with the MT68. The MT65 for me is nostalgic as it was the first version I played that belonged to my Uncle in Puerto Rico when I was a child. He gave it to me when I turned 19. I rebuilt it so it would be like new. I tend to buy second keyboards of models I like to tinker with. The MT52 is also of nostalgic value to me as my dad bought that for me back in 1988. The chips in it are different from the MT65 but it DOES have tinkering abilities and as such I bought 2 CT320 full sized keyboard versions of this MT52 so I would leave my rare White MT52 intact. Back to the subject of the PT31. Buy a small 2.2kb tuning pot on ebay and put that back. The reset "P" is just a metal hovering over another metal. BUT, if you feel safer to install you can install and normally open push switch and install it on the back of the Casio and when or if the memory needs reset, viola! As for small formfactor Casios that have the same or close type chips as the MT65, there are some rare PT style boombox KX101 which has a polyphonic keyboard that corresponds to a MT model. The VL5 with LCD and calculator buttons is also polyphonic and also corresponds to a MT model which is maybe MT30 or MT31 or M10.? Cyberyogi has more info on these and I indeed found my info from his site.

[534N]

@pianokeyjoe - ah, I agree that it’s a good idea to play around with models that are less desirable but my girlfriend is becoming more critical of my keyboard collection lately and I don’t think the big ones will fly under the radar at all. Maybe that’s another reason I’m starting to love the PT-sized stuff. They are easier to hide away and they take up less space so they are a little bit more justifiable, for me anyway.

 

The MT-68 is more special for me than the 65 for the moment, but I haven’t received the 65 yet so it may change my mind. My 68 has slider pieces and a volume knob salvaged from other MT-68/65s. I kind of like it for the idea that it’s kind of a makeshift space junker like a Star Wars ship and it was really cared for throughout its lifetime, despite the scratches. I can’t wait to compare it to the 65. Hopefully there are no hidden surprises for me to find when I get it. The guy showed it to me in a video but the language barrier prevented me from checking every function.

 

Anyway, thanks for the info on the similar models. The boombox looks interesting, but I imagine it’s really hard to find. Maybe it’s bigger than I want also. Hmm.. I’ll keep an eye out for it. Looks like it would make an awesome show piece if nothing else.

 

I just ordered the 2k variable resister pot and I should get it in 2 weeks. By that time, I will be on an extended vacation time so hopefully I will have enough extra time to get to the bottom of this PT-31 mystery. I will look for a suitable switch for the reset function also. Would you happen to have a recommendation for that? I’m not sure I can imagine it yet.

Edited November 30, 2022 by 534N

[CYBERYOGI =CO=Windler]

MT-52 has different firmware in its NEC D930G CPU than MT-65/68, thus they likely can not be upgraded. (I haven't analyzed the keymatrix by myself yet.)

 

software number	hardware class	notes & features
011	MT-65, CT-7000, RC-1	original version with 3x4 accompaniment variations
013	CT-620	61 keys support (changed matrix layout), arpeggio & bass volume pins swapped
017	MT-800 (old)	ROM-Pack support, different preset sounds & rhythms
018	MT-85, MT-800 (new)	same like 017? (bugfix release?)
019	MT-210	uses percussion IC M6202-19, some preset sounds changed
020	MT-52	Super Drums support, different preset sounds & rhythms
022	MT-500	Super Drums support, uses percussion IC D934G, different preset sounds & rhythms

 

The Casio KX-101 is no relative of MT-65 either but rather a 4-note polyphonic sort-of PT-30 with very different software.

• CPU1= "NEC D1868G 006" (80 pin SMD)
• CPU2= "NEC D1879G 002" (80 pin SMD)

The D1868G with different firmware was else used in PT-30-like keyboards.

 

software number	hardware class	notes & features
001	PT-30	LCD support + datasette module, uses SRAM HD61914B
004	PT-50	LCD & ROM-Pack support + datasette module, uses 2x SRAM HD61914B
006	KX-101	combined with "NEC D1879G 002", uses 2x SRAM HD61914C, datasette storage
007	PT-80	ROM-Pack & key leds support
A01 (HD61703)	MT-18	same like 007
B01 (HD61703)	PT-82	ROM-Pack & key leds support, no chord buttons

 

 

 

[534N]

@CYBERYOGI =CO=Windler - Nice detailed info. I really appreciate that. 
 

So there’s no cross-over between the MT-65 capabilities and the Super Drums variable patterns? Bummer..

 

Too bad the MT-65 stuff didn’t get developed further and physically downsized. It would be the ultimate casual home keyboard to this day. I think a lot of modern stuff adds too many bells and whistles. I want a PT-30 + MT-65 + added 400v functions in a tiny package.

 

Oh well.. guess I just have to appreciate what’s already there.

[pianokeyjoe]

2 hours ago, 534N said:

@CYBERYOGI =CO=Windler - Nice detailed info. I really appreciate that. 
 

So there’s no cross-over between the MT-65 capabilities and the Super Drums variable patterns? Bummer..

 

Too bad the MT-65 stuff didn’t get developed further and physically downsized. It would be the ultimate casual home keyboard to this day. I think a lot of modern stuff adds too many bells and whistles. I want a PT-30 + MT-65 + added 400v functions in a tiny package.

 

Oh well.. guess I just have to appreciate what’s already there.

LOL! We must be of a like minded kindred spirit my good sir! I too would want such a keyboard and have indeed DREAMED of such unusual PT sized Casio keyboards throughout my lifetime since I started playing keys back in 1987! The PT30/MT65/400V keyboard has been in my dreams 2 or 3 times and I always found it in a used music gear shop that does not exist. It is White and is slimmer than the PT30 but wider than the PT20 and as long as the MT65. All of which are WHITE model keyboards lol! Love them white Casios!

[534N]

@pianokeyjoe- I’ve had dreams about finding musical treasure like that. I wonder if this keyboard idea will come up in my dreams also. I’m a bass and guitar player mainly but I’ve recently gotten hooked on these little toy-like keyboards and I can’t stop thinking about them. It seems the general rule for these things for me to like them is that they have to be from the early 80s or they don’t seem very cool. I can’t understand why on earth Casio stopped continuing the evolution with their early vision. The auto-accompaniment, arpeggiator, analog drums, etc.. They had an amazing thing started.

 

Anyway, my white MT-65 should arrive today. I hope when I open the case, I will suddenly become obsessed with the white models. The white PT-30 is a lot easier to find and I can keep my grey models for modification projects. Can’t wait!

 

Has anyone done an isolated output for each instrument kind of mod yet? Curious to hear how that turned out if anyone has done it. For me, this would be the best thing to do. That arpeggiator would be killer if it could be separated and run through effects like tremolo, delay, long reverb, chorus, etc. The isolated bass would be amazing isolated through a synth bass octave pedal to get a fatter dub sound. Drool.. 

 

I don’t want to get too off topic here, but has anyone tried the Yamaha MK-100? That’s the model that got me started. I bought it on a whim and research of similar keyboards has led me to all these great Casio models. Could be a fun one if anyone wants to explore a different brand. The drums and accompaniment styles are not as good, in my opinion, but it adds some very unique features that I haven’t seen anywhere else.

[CYBERYOGI =CO=Windler]

Microcontrollers of that era had very little internal rom , so Casio had to throw features out to add additional ones. The SuperDrums patterns or ROM-Pack support likely consume enough bytes to kick out the number tables for the synth features, despite the chip core was the same.

 

I have identified separate sound channels in MT-65 hardware platform (D930G+D931C). On my CT-410V I had to install an additional analogue envelope PCB to retrofit the arpeggio. I hope this doesn't go too off-topic. This chip has nothing to do with PT-30.

pinout D930G

The Accompaniment LSI "NEC D930G 011" (80 pin SMD, pins count anticlockwise) is one of the most interesting squarewave accompaniment CPUs ever made by Casio, because although it features only 12 rhythms, it has for each of them 4 chord, 4 bass and 4 arpeggio variants and features wonderful dark and sonorously droning multipulse squarewave bass and chord tones with different pulse patterns. It is 6 note polyphonic (4 chord channels, bass, arpeggio), and all tones have separate output lines (those partly need external envelope capacitors). It features also separate outputs for 7 analogue percussion trigger pulses and a static percussion waveform (2 mixed shift register feedback noises) for snare and hihats. Drums and clave timbre are made from external analogue circuits. The D930G also acts as keyboard matrix decoder for keys, control switches and accompaniment section keys. It contains in its ROM also definitions for main voice preset sounds those it can output through a 4 bit bus to the external main voice sound IC D931C (e.g. in CT-410V); in other instruments (e.g. Casio MT-45) this feature is not used. The keyboard matrix outputs are multiplexed as address bus out in keyboards with additional rom, ram or percussion IC (seen in MT-500 service manual); the data bus has only 4 bit. The "D930G 011" can also be controlled by an external CPU (e.g. D7801G used in Casiotone 7000 or the Symphonytron 8000 accompaniment unit RC-1 - both control also D931C from there instead of connecting it with D930G).

 

The switchable multi-track accompaniment is detailedly described in the US patent 4624170.

Other variants of "NEC D930G xxx" ("xxx" = software number of internal ROM) differ in accompaniments, preset sounds and have additional features those typically reduce the count of accompaniment variations (likely due to limited internal ROM space). The Technical Guide For Casiotone from 1986 mentions software number 018 also for MT-800 (mine has 017) thus it may be a bugfix release. 
 

software number	hardware class	notes & features
011	MT-65, CT-7000, RC-1	original version with 3x4 accompaniment variations
013	CT-620	61 keys support (changed matrix layout), arpeggio & bass volume pins swapped
017	MT-800 (old)	ROM-Pack support, different preset sounds & rhythms
018	MT-85, MT-800 (new)	same like 017? (bugfix release?)
019	MT-210	uses percussion IC M6202-19, some preset sounds changed
020	MT-52	Super Drums support, different preset sounds & rhythms
022	MT-500	Super Drums support, uses percussion IC D934G, different preset sounds & rhythms

 

This pinout was based on the service manuals of Casio CT-405/MT-65/MT-68/MT-100, CT-620, MT-52 and MT-500. Apparently all "O-#" pins are outputs, "I-#" are inputs. "DB-#" are data bus.
 

pin name purpose 1 O-34 chord wave out 2 O-35 chord wave out 3 O-36 chord wave out 4 O-37 chord wave out (only 7th) 5 O-38 bass wave out 6 O-39 arpeggio wave out 7 O-40 chord envelope out 8 O-41 chord envelope out 9 O-42 chord envelope out 10 O-43 chord envelope out 11 O-44 bass envelope out 12 O-45 arpeggio envelope out | in MT-500: bass trigger 13 O-46 base drum trigger out | in MT-500: chord trigger 14 O-47 snare drum trigger out | in MT-500: chord trigger 15 GND2 ground 0V (wired to GND) 16 O-48 low conga trigger out | in MT-500: chord trigger 17 O-49 high conga trigger out | in MT-500: chord trigger 18 O-50 claves trigger out | in MT-52: rimshot trigger 19 O-51 hihat trigger out | in MT-52: cymbal & hihat trigger 20 O-52 cymbal trigger out 21 O-53   22 O-54 white noise1 out (for cymbal, hihat, snare) 23 O-55 white noise2 out (externally mixed with O-54) 24 /   25 I-3 (wired to ground) 26 O-32 in MT-500: drum pad latch clock T1 out 27 O-33   28 I-1 /reset 29 O-25 /APO auto-power-off out 30 OSC   31 I-7 (used in Casio RC-1, CT-7000) 32 I-8 clock in 1.6MHz (from D931C pin CLK3) 33 VDD supply voltage +5V 34 O-26 main voice strobe B (to D931C pin I-2) 35 O-27 main voice strobe A (to D931C pin I-1) 36 O-28 main voice data out (to D931C pin DB-1) 37 O-29 main voice data out (to D931C pin DB-2) 38 O-30 main voice data out (to D931C pin DB-3)  39 O-31 main voice data out (to D931C pin DB-4) 40 I-6 (wired to VDD)

pin name purpose 41 I-5 (wired to VDD) 42 I-4 (wired to VDD) | in MT-500: drumpad interrupt /INT in 43 I-2 tempo clock in 44 KI8 key matrix in 45 KI7 key matrix in 46 KI6 key matrix in 47 KI5 key matrix in 48 KI4 key matrix in 49 KI3 key matrix in 50 KI2 key matrix in 51 KI1 key matrix in 52 KC1 key matrix out, address bus A0 out 53 KC2 key matrix out, address bus A1 out 54 KC3 key matrix out, address bus A2 out 55 KC4 key matrix out, address bus A3 out 56 KC5 key matrix out, address bus A4 out 57 KC6 key matrix out, address bus A5 out 58 KC7 key matrix out, address bus A6 out 59 KC8 key matrix out, address bus A7 out 60 KC9 key matrix out, address bus A8 out 61 KC10 key matrix out, address bus A9 out 62 O-11 in MT-500: rom CS out 63 O-12 in MT-500: rom CS out 64 O-24 in MT-500: ram WE,  percussion ic CS 65 DB-4 data bus (ram, rom, percussion ic, drumpads) 66 DB-3 data bus (ram, rom, percussion ic, drumpads) 67 DB-2 data bus (ram, rom, percussion ic, drumpads) 68 DB-1 data bus (ram, rom, percussion ic, drumpads) 69 O-23   70 O-22 KC20 key matrix out 71 O-21 KC19 key matrix out 72 GND ground 0V 73 O-20 tempo led out, address bus A13 out 74 O-19 address bus A12 out | in CT-620: KC21 key matrix out 75 O-18 address bus A11 out 76 O-17 address bus A10 out 77 O-16 in MT-500: chord filter switch out (H=dull, L=short release)  78 O-15 in MT-500: chord release out (H=long, L=short) 79 O-14 arpeggio volume out | in CT-620: bass volume | in MT-52: /hihat cymbal select | in MT-500: tempo led 80 O-13 bass volume out | in CT-620: arpeggio volume | in MT-500: auto bd led

 

Many unused pins of D930G version "011" (e.g. data bus) have a meaning in other software numbers. E.g. MT-800 ("017") supports a ROM-Pack slot and MT-500 ("022") a sample percussion IC; both also have additional RAM. In the MT-500 4 drumpads are buffered in a latch that is clocked by pin 26 to output its 4 signals to the data bus (pin 65..68). According to its service manual, a 4-input NOR triggers an interrupt at pin 42 when multiple (or any?) drumpads are hit. Pin 73 selects the active nibble of the 8 bit percussion ROM to be read through the 4 bit data bus.

Apparently a direct predecessor of this hardware class was the accompaniment CPU D910G with main voice sound IC D990G, those were used in Casio MT-60.

 

Edited December 1, 2022 by CYBERYOGI =CO=Windler

[534N]

@CYBERYOGI =CO=Windler - Wow, that is super thorough info. Thank you. This will come in handy when I start to look into the possibilities of modding my MT-68 or 65. The 65 just came in today and it looks very good after I cleaned it up a bit. I guess that means the 68 will become a future mod project. That seems to make more sense.

 

I think I only want to add isolated output jacks  on the MT models since I imagine that would be a more simple mod. Having a transpose option would be really great though too, if it's not too complicated. I will have to research that for awhile. I wonder what the best type of part would be for rotating through the levels of transposition so the processor understands clearly. That's a question for later.. I better focus on what I can do for now.

 

I think my first projects will just be to fix the PT-31 and the MT-400v. I'm just waiting for the 2k trim pot to come in for the PT-31 and I think I will open up the 400v further during my December vacation and continue on that thread again with my findings. Thank you so much for the continued interest.  Your responses make this journey a lot more exciting.

[CYBERYOGI =CO=Windler]

The transpose in MT-65 is a digital feature on the CPU. You only have to push a button and press a key to transpose to that note. If I remember well, additionally the "transpose on" switch is needed to activate this mode.

keyboard matrix

This matrix was initially analyzed by me, but later I filled gaps and fixed some bugs using Robin Whittle's essay and the Casio MT-65/ MT-100/ CT-405 service manual.
 

51 KI1	50 KI2	49 KI3	48 KI4	47 KI5	46 KI6	45 KI7	44 KI8		CPU pin
in 1	in 2	in 3	in 4	in 5	in 6	in 7	in 8	in / out
o C1	o C#1	o D1	o D#1	o E1	o F1			out 1	52 KC1
o F#1	o G1	o G#1	o A1	o A#1	o B1	APO disable	C. memory mode	out 2	53 KC2
o C2	o C#2	o D2	o D#2	o E2	o F2	C. casio	C. fingered	out 3	54 KC3
o F#2	o G2	o G#2	o A2	o A#2	o B2	C. manual bass	C. arpeggio on	out 4	55 KC4
o C3	o C#3	o D3	o D#3	o E3	o F3			out 5	56 KC5
o F#3	o G3	o G#3	o A3	o A#3	o B3		key hold	out 6	57 KC6
o C4	o C#4	o D4	o D#4	o E4	o F4	C. memory	octave down	out 7	58 KC7
o F#4	o G4	o G#4	o A4	o A#4	o B4	transpose on	transpose set	out 8	59 KC8
o C5	R. synchro	R. start/stop	R. fill-in	O. envelope 1	O. envelope 2	O. select	R. select	out 9	60 KC9
O. pipe organ	O. flute	O. trumpet	O. oboe	O. violin	O. bank switch			out 10	61 KC10
C. bass 2	C. bass 3	C. chord 2	C. chord 3	O. sustain	O. vibrato	O. delayed vibrato	O. reverb.	out 11	71 KC19
R. rock	R. pops	R. disco	R. 16 beat	R. swing	R. latin swing	C. arpeggio 2	C. arpeggio 3	out 12	70 KC20

All unknown function names and in/ out numbers in this chart were chosen by me. The input lines are active- low, i.e. react on GND, thus any functions are triggered by a switch in series to a diode from one "in" to one "out" pin.
 

legend:
"o"	= keyboard key
underlined	= function needs locking switch (i.e. stays active only so long the switch is closed)
R.	= rhythm
C.	= chord
O.	= orchestra (main voice sound)
orange background	= easteregg (unconnected feature)

 

octave down

A switch here transposes the main voice 1 octave down (works only in chord mode).

 

 

[534N]

@CYBERYOGI =CO=Windler - You make it sound like it's possibly a lot easier than I was expecting. I need to put a button somewhere that interacts with the chip to say the transpose function is temporarily "ON" while I press any key other than C and it will move everything relative to that? I wonder how you would activate transpose up vs transpose down though. Hmm.. (I am editing this afterward because I thought about it a bit more)

 

I understand the concept, but actually physically executing this will take some time to understand I'm sure. I see this as a long term goal but it's nice to know that there's a path to it that doesn't sound too wild or dangerous. I appreciate the info

Edited December 2, 2022 by 534N

[534N]

@CYBERYOGI =CO=Windler - I see there is also arpeggio 1 and 2 unlockable features. Would you just set a button for these also? 
 

If you don’t mind me asking, what would be the most ideal way to activate these features as a physical mechanism on the outside? I imagine individual slide switches.. but maybe that would interfere with the already-existing slide switch for (what I assume is) arpeggiator pattern 1.

[pianokeyjoe]

4 hours ago, 534N said:

@CYBERYOGI =CO=Windler - I see there is also arpeggio 1 and 2 unlockable features. Would you just set a button for these also? 
 

If you don’t mind me asking, what would be the most ideal way to activate these features as a physical mechanism on the outside? I imagine individual slide switches.. but maybe that would interfere with the already-existing slide switch for (what I assume is) arpeggiator pattern 1.

Oh my friend, worry not about the many extras if you are referring to the MT65/68. Those features are already active on those 2 keyboards . The transpose which is NOT on the MT65/68 would be the only thing from what I see, that you need to worry about. Also, making an interface for the individual outputs for:Bass,Chord,Arpeggios and Base drum,snare drum,claves,congas,hihat short,hihat long. Those are the only things you need to worry about on the MT65/68. The MT400V if you fix it, THAT is another story!! That keyboard is the one you will need to worry about all those MT65 features being activated and since the MT400V does NOT have built in speakers, I reckon you will have some room for those features and the corresponding switches and jacks.

[534N]

@pianokeyjoe- The extra arpeggio patterns are already active? I thought it was just an on/off switch with one standardized arpeggio pattern for each rhythm. It’s possible I’m misunderstanding the meaning of arpeggio 2 and 3 though.

 

The more I think about it, the more I feel like the transpose option isn’t really important. It would be nice for “cheating” and staying on the white keys though. Admittedly, I’m not so great at playing keys. I mostly just use them to record one part at a time.

 

Anyway, I am definitely not ready to go into more serious modding yet, but it’s interesting to start thinking about it. If it involves any soldering on the processor component, I will probably be too afraid to make a mistake. Those little leads coming off are too close together for me to feel any level of confidence on an irreplaceable part like that.

 

The isolated multi-output mod will probably satisfy me. But I want to understand the arpeggio possibilities too.. Could there be more?

[pianokeyjoe]

The arpeggio setting on the MT65/68 is ON, 1,2,3,4 as well as the Bass pattern and Chord pattern. They are labelled with Roman numerals I,II,III, and IV . You have plenty to enjoy no mods needed on the MT65/68. The individual parts output mods is the only thing you would need and I mean by that, volume or muting mods so you can mute and unmute the individual drums and auto accompaniment sections. Yeah transpose is nice especially when you can not really play the black keys I know lol!

[534N]

@pianokeyjoe- Ahh.. I made a huge mistake! I was not looking at my keyboard when I posted my response. There's an arpeggiator on/off switch, but there is also a 4-way selector switch for different patterns when that switch is ON. I tend to respond to this thread in the late evening when I've already been exhausted by my daily work. That's my excuse for the moment.. but I feel a bit foolish too.

Well.. I guess I have to brush that off and move forward with more focus. I appreciate your efforts to pull me back towards a basic understanding without shaming me, and I'm glad we have similar visions of what the ultimate "toy" keyboard should be. I think we both appreciate the auto-accompaniment options and the unique tones of these models. There's a special quality that nothing else seems able to create authentically.

 

I look forward to the direction of this discussion as my time gets freed up over the coming month. For me, it's a slow process of trying to figure out the right questions to ask (when I have the time) and then trying to understand the answers, and then correctly executing the actions that achieve the goal.

I don't have any updates for anything at the moment because it's a busy week. But I'm curious to hear about anyone's current project with modification, repair or dreaming up new things.

Edited December 3, 2022 by 534N

[CYBERYOGI =CO=Windler]

For transpose you will need a locking switch "transpose on" to enable it, and a push button "transpose set". If I remember well, you hold that button, press and release the key it shall transpose to, and then release the button.

 

The arpeggios and synth features are already fully enabled in MT-65/68. Only in crippled keyboards like CT-410V/MT-400V, MT-100 or CK-500 will need that surgery.

Edited December 4, 2022 by CYBERYOGI =CO=Windler

[Chas]

@534N - Sorry I didn't respond earlier with potentiometer details. It's been a busy week..

 

This is the original damaged trim pot from my PT80. Like your PT31, it appeared to have been damaged by someone poking it via the access hole causing two of the legs to break.. 

 

 

The next two pictures are of the damaged trim pot (yellow) next to the replacement trim pot (blue). The value on them is 472, though it's so long ago that I bought them and repaired my PT80,  that I cannot remember what  the number on them translates to in electrical resistance terms.

 

 

 

 

The value doesn't have to be 100% exact though,  and replacing them with a potentiometer with a wider range is what circuit benders used to do to allow wilder pitch shifting. There is a limit though,  as I think if you try to go too high or low, then the sound will simply cut off as the CPU decides that the value is out of range. 

[CYBERYOGI =CO=Windler]

472 means 47 with 2x 0 = 4.7k (4.7 kOhm aka 4700 ohm).

 

I doubt that it fell off by getting mauled by screwdriver. That would make rather the rotary part crack off but the bottom stays in place. I suspect the pins to be corroded off by battery acid, which makes it likely that also other components got damaged.

[534N]

@CYBERYOGI =CO=Windler - I will probably have to stay away from that mod because I don't understand what kind of switch can do that or where to connect it. That's ok. Maybe it's not my place to dig into that level of electronics. I want to someday, but I feel like I would likely get in over my head very quickly if I were to even attempt the first steps. I will remember you for future modification explorations.

 

For now, I think I will stick to the easier modifications.

 

@Chas- Ah.. it's too bad I already ordered a different part. I don't know if the part is the same between the 2 models anyway.. I wasn't sure when I would get a response so I ordered a 2k pot to expedite the shipping process. I saw 2.2kb printed on the board in that spot so I went with the best guess I could figure. It's odd that it says "kb" though.. Why doesn't it just say 2k? I feel like I'm missing something. What does the B stand for in 2.2kB? I'm clueless. At least it was only a dollar or so.. if it's not right, I just have a bag of useless doodads in a drawer I guess.

 

Can anyone clarify the "kb" thing?

 

@CYBERYOGI =CO=Windler - I don't doubt your expertise at all. But I do find it odd that the only destroyed parts I can find on this whole keyboard are exactly where someone would stick a screwdriver in. Why wouldn't any other parts have damage?

 

I understand there is possibly damage I can't see.. but really.. Everything looks very clean and tidy except for those 2 exact spots. They are physically broken unlike anything else. There is no other physical damage at all.

 

But I still don't doubt that it could be a combination of issues though..

 

Has anyone lost any hair from this stuff? Haha

[pianokeyjoe]

So I got my second PT20 and found that it indeed has issues with battery acid leak. Some of the traces on the PCB around the power input area and battery terminal area are either eaten away or on the verge. I have done some cleaning and repaired the traces that needed it and I have full power but the unit still would not make a sound and none of the controls reacted. After a few seconds of fussing with it it will shut off on its own. I did some MORE checking and discovered that several pins of the RIBBON CABLE were corroded and eaten away but you can not tell until you desolder the ribbon and the connections break off. So? @534NWhen you get that vacation, check your ribbon cables! You may in fact have corroded and broken connections between boards! Using a needle tip 15Watt pencil soldering iron like those from RadioShack, you will be better able to solder and desolder the ribbons. Best way to check the connections is by testing continuity BUT be WARNED! I checked that way FIRST and all pins checked out fine! So you may need at this point, to just desolder the ribbon from the main board to the control board, paying mind to PIN #1 on both boards. Yeah, I was convinced a dead CPU, but that acid is insidious and you really DO have to almost rebuild the Casio PT31 after such calamity. IF you decide not to tackle this yourself, tell you tech all this I have said about my PT20.. It may help guide him in a direction to go on at least to start. 

Edited December 6, 2022 by pianokeyjoe
New information

[ctt956]

I recently got a PT-20 that had the same issue at first after cleaning leakage from batteries that expired 21 years ago, with the exception of not responding to any keys or buttons. I don't remember if I tried the reset button. For the first time testing, I did use 4 Eneloops and one Energizer rechargeable AA (all were fully charged). I opened it to inspect for damage, and found the boards to be miraculously unharmed from the battery leakage – the foam pad on the battery door was the only total loss. I didn't see anything obviously damaged on the inside, so I put the batteries back in to check voltages. This time I had found another Eneloop, so I used all Eneloops, and it worked perfectly! I don't know if it just had an odd reaction to the one Energizer, it needed some extra persuasion to wake up from its quarter century hibernation, or opening the case moved something to make it work, but that was a surprisingly easy fix! Though it does still have a slight hiss in the background.

[pianokeyjoe]

@ctt956Hi! Well congrats on your PT20 score! Yeah I now have 2 of them and both do not work right. The one I just bought DOES have acid leak damage on the mainboard in the area where the battery terminal wires connect and while I did check continuity and only found ONE trace eaten up and I fixed it, the unit still does not respond to keys or buttons. When I plug it in and the switch is OFF, it stays one no matter what, unless I press the P reset underneath, then it goes off and stays off even with the switch ON, until I unplug it and plug it in again. CPU lock up seems to be the issue there. I have another one that also had the battery leak but I was able to fix that one partly.. It turns on and off normally but when I play it, the power light dims, the sound is in a different "tuning" and then I release the key, and the sound trails, the pitch goes up, and the led light get bright again. It is acting like it is not getting enough power. Like when you play it with dying batteries. That is how it sounds. But I think I already know what it is so I will attempt a fix on that and report back. Sadly for @534Nhis unit is a PT31 which by my looking at the outside of it, seemed to have been wet or something and he did state there was battery acid crust in the compartment(sad tell tale sign of doom), and broken tuning trim pot inside as well as the P reset contacts missing. His does not power on AT ALL. I am thinking dead CPU among a few other things which may be related to battery acid leak. At least it is not urine in the keyboard lol! I have a dead Yamaha PSR70 with that horrible damage and yes, it stinks!

[CYBERYOGI =CO=Windler]

If the PCB is marked 2.2k but a 4.7k trimmer was installed, it may work with 2.2k as well. But if it needs 4.7k, then 2.2k will likely play it with (possibly more than 1 octave) too high pitch or at least can not be tuned as low as it should. Of course idiots with screwdrivers, pens or needles can cause all kinds of mayhem in electronics. Look how the fracture surface of the cracked pin looks - if it is discoloured (green?) then it likely was battery acid.

 

Damage by battery acid (actually rather an alkaline substance unless you still use zinc-carbon cells) also depends on how moist (it corrodes stronger in humid air) and in which orientation it was stored (liquid flow down, not up), although evaporation also furthers corrosion when it can't get out quick enough. Hence a wet basement or garage or rainy fleamarket may be much worse than a warm and dry livingroom.

 

Casio ribbon cables with metal wires inside are easy to patch by resoldering or soldering wires across. Only the LCD cables (foil with printed carbon paint) are basically impossible to fix if cracked or decomposed.

 

The switches and buttons in MT-65 variants I mentioned need to be wired with a diode in series between each 2 pins of the keyboard matrix (CPU pin numbers are listed in the table). It needs some basic electronics knowledge and soldering skill to do that. (Do not solder directly to tiny SMD chip pins but follow their trace to an easier to reach spot.)

Edited December 6, 2022 by CYBERYOGI =CO=Windler