Riva Lima Posted January 11 Share Posted January 11 (edited) Hey, guys! I hope everyone is well... I bought a classic MT400V, but it came with a problem, of course I bought it at a lower price than normal, as this problem is affecting it... the keys don't work, except the main part. accompaniment, all the keys in this section respond to the accompaniment chords... however in 'solo' mode none of the keys work, even with the accompaniment activated, the rest of the keys do not contain any sound! I've already opened it and it doesn't contain any stains of corrosion from the battery, apparently everything is clean from the factory... any idea what could be happening? Yes, it came sounds with the speakers and the L and R output sound connected to the normal keyboard outputs. Edited January 11 by Riva Lima error Quote Link to comment Share on other sites More sharing options...
briefer Posted January 11 Share Posted January 11 May be a dead capacitor, you can desolder and check them. But is is a lot of work. I have an MT 65 with the same symptoms, but if I leave it powered on it works after a couple of minutes, Typical of a faulty capacitor. Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 12 Author Share Posted January 12 8 hours ago, briefer said: Pode ser um capacitor morto, você pode dessoldar e verificá-los. Mas é muito trabalho. Tenho um MT 65 com os mesmos sintomas, mas se deixar ligado ele funciona depois de alguns minutos, típico de capacitor com defeito. Maybe it would be a resistor... but I did a visual inspection and didn't see any leaky or bulging capacitors Quote Link to comment Share on other sites More sharing options...
pianokeyjoe Posted January 12 Share Posted January 12 This sounds like a popped resistor or the cpu for the main sounds went bad. However, check the melody volume slider. Seriously, check the volume slider. The accompaniment section has a different cpu for it as well as different volume controls for it separate from the melody(main voices)section. check for solder or wire joints and the simplest.. spray electronic contact cleaner that has teflon or some other lubricant in it! Has to be lubricated ELECTRONIC contact cleaner, not ELECTRIC/TV contact cleaner! vigorously slide that sucker left and right to see if you hear static and sound while holding down some melody keys, say in the upper octaves? Report back what you come up with. Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 12 Author Share Posted January 12 (edited) 2 horas atrás, pianokeyjoe disse: Isso é como um resistor estourado ou a CPU dos filhos principais estragou. No entanto, verifique o controle deslizante de volume da melodia. Sério, verifique o controle deslizante de volume. A seção de acompanhamento tem uma CPU diferente, bem como controles de volume diferentes, separados da seção de melodia (vozes principais). verifique se há juntas de solda ou fio e o mais simples... borrife um limpador de contatos eletrônicos que contenha teflon ou algum outro financiamento! Deve ser lubrificado com limpadores de contato ELETRÔNICO, não com limpadores de contato ELÉTRICO/TV! deslize vigorosamente aquele ventosa para a esquerda e para a direita para ver se você ouve estática e som enquanto mantém pressionadas algumas teclas de melodia, bem nas oitavas superiores? Relate o que você descobriu. Many thanks for the reply! Unfortunately, I didn't find any service manual, so I don't know exactly which resistor would be damaged, without specific guidance on where it would be on the board, it's difficult to identify where it would come from... of course, I have a multimeter, but measuring resistor by resistor, it's a very arduous and difficult task but I will try the other tips which are also important! But it would be very interesting to know where exactly the resistor would be... I looked for a service manual for it and unfortunately I couldn't find it anywhere. Edited January 12 by Riva Lima error Quote Link to comment Share on other sites More sharing options...
briefer Posted January 12 Share Posted January 12 Maybe you can check if any resistor is hot by touching them, with the keyboard powered off. Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 12 Author Share Posted January 12 1 hour ago, briefer said: Talvez você possa verificar se algum resistor está quente tocando nele, com o teclado desligado. I will try this, thanks! Quote Link to comment Share on other sites More sharing options...
Chas Posted January 12 Share Posted January 12 Look for an MT65/ 68/ CT405 service manual. They share almost identical hardware and features with the MT400V/ CT410V models. The tone sets and rhythms/ accompaniment section are the same. They lack the analogue filter of the 400V/ 410V, and have a couple of extra features, but otherwise they are identical. Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 13 Author Share Posted January 13 8 hours ago, briefer said: Talvez você possa verificar se algum resistor está quente tocando nele, com o teclado desligado. This 220r 1/4W resistor is getting very hot, is it the culprit, or is some component nearby causing it to get hot? Quote Link to comment Share on other sites More sharing options...
briefer Posted January 13 Share Posted January 13 (edited) That green thing in the photo seems like a voltage regulator, and they always run hot (at least the ones built in the 80s). You should check the service manual (as Chas mentions) to see the voltage that should be delivered by that regulator. Maybe the faulty part of the keyboard depends on it. Edit: nevermind, that green thing it is a transistor (2sb507f). Did you check the resistor with your multimeter? Link to the service manual: https://www.synthxl.com/wp-content/uploads/2020/04/Casio-CT-405-MT-65-68-Service-Manual.pdf Edited January 13 by briefer Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 13 Author Share Posted January 13 9 hours ago, briefer said: Aquela coisa verde da foto parece um regulador de tensão, e eles sempre esquentam (pelo menos os construídos nos anos 80). Você deve verificar o manual de serviço (como Chas menciona) para ver a tensão que deve ser fornecida por aquele regulador. Talvez a parte defeituosa do teclado dependa disso. Edit: deixa pra lá, aquela coisa verde é um transistor (2sb507f). Você verificou o resistor com seu multímetro? Link para o manual de serviço: https://www.synthxl.com/wp-content/uploads/2020/04/Casio-CT-405-MT-65-68-Service-Manual.pdf Hello again! Yes, I did the tests with the multimeter measuring the resistor that is heating up, and its value is still within, no changes... also the transistor, it is in perfect condition... I'm back to square one... the accompanying sliders , rhythm, all of them, are working normally... no sound from the keys yet... mystery... without the specific electrical diagram for it, it gets very complicated, and the service manuals for other MTs are very confusing For me, apart from the fact that some components are on different boards, it is much more difficult to interpret. Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 14 Author Share Posted January 14 On 1/12/2024 at 9:04 AM, pianokeyjoe said: This sounds like a popped resistor or the cpu for the main sounds went bad. However, check the melody volume slider. Seriously, check the volume slider. The accompaniment section has a different cpu for it as well as different volume controls for it separate from the melody(main voices)section. check for solder or wire joints and the simplest.. spray electronic contact cleaner that has teflon or some other lubricant in it! Has to be lubricated ELECTRONIC contact cleaner, not ELECTRIC/TV contact cleaner! vigorously slide that sucker left and right to see if you hear static and sound while holding down some melody keys, say in the upper octaves? Report back what you come up with. Here's an interesting detail that I only noticed after increasing the amplifier volume a lot... it's possible to hear the notes, but at a very low volume, beneath the amplification noise... can you hear them? Quote Link to comment Share on other sites More sharing options...
Chas Posted January 14 Share Posted January 14 Focusing on one component because it is getting hot will be unlikely to solve your issue. The component itself might be faulty, or it could be components elsewhere that are faulty and causing the resistor to run hot. If you replace the running hot component you might end up with the new component doing the exact same thing. That's the whole purpose of a service manual. It will have details and test points with information on what you should be reading at those test points. That will help you to isolate where the problem is most likely to be. Saying that, as you are actually getting some very quiet sounds from the Tone section, that does indicate that the tone generating part of the keyboard is still functioning. Even though it's very quiet, can you select different Tones and hear the Tone change when you play the keys? If so, that might suggest an issue between the 931C Tone Generator and the mixer output sections. I've copied a page out of the MT65/ 68/ 405 Service Manual that shows a block diagram and how the Rhythm, Accompaniment and Tone sections of the Casio are all brought to the final output. As you can see, Accomp goes to Mixer 1 and Rhythm goes to Mixer 2, then these both are brought together into Mixer 3 before being fed to Mixer 4. The MT400V is slightly different as it lacks the arpeggiator section, but the point being is that the Accomp and Rhythm sections are brought together at Mixer 3, which is then fed into Mixer 4. Note that the D931 Melody (the "Tones") also gets fed into Mixer 4, and then all sections of the keyboard are controlled by a master volume. Point being, if you can hear the accomp and rhythm sections perfectly well, that rules out any issue with the Master Volume slider (potentiometer) and likely no issue with Mixer 4. Therefore you would need to work back from Mixer 4 and look at the path that the D931 Melody signal takes. After the Tone signal leaves the D931 Tone generator it passes through a D/A converter, a Sample/ Hold circuit and also a Low Pass Filter before being fed into Mixer 4. Unless there is any connection issues at Mixer 4, the problem is most likely somewhere in the three sections before it. Only by testing each of those circuits following the Service Manual schematics will you be able to pin point the problem. 1 Quote Link to comment Share on other sites More sharing options...
pianokeyjoe Posted January 14 Share Posted January 14 uh man! I had the same issue with my MT500 and I fixed it and now since it has been years(2018), I forgot what I fixed on it lol! I do know it was some simple component and not a transistor or ic. I think it was a diode as that is easy to check while in the circuit and they tend to act like a fuse that can blow easily when you tamper with the wrong circuits trying to circuit bend lol.. Oh my circuitbending dayz :D. The other could very well BE a resistor but assuming you nor the previous owner did any circuit bending and the battery situation is good, then you need to check the ribbon cables that go between the mainboard(biggest board) and the POWER/audio amplifier board(the board with your DC power jack and audio jacks). It could be also that some one tried using a center positive 9vdc power supply instead of the correct but harder to find negative center 7.5vdc power supply and that caused a diode to pop between the amplifier IC and the tone gen ic.. COme to think of it I think thats IT! Check the amp section. I hear the buzzing of the casio itself, and it is different with every sound you select so yes, all is well with the logic side of things, you need to concentrate now of the audio amp ic and test the resistors and mainly the diodes around that as those diodes would be used to prevent audio feedback and voltage back feed between ic chips, etc. You almost there my friend! 1 Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 14 Author Share Posted January 14 2 hours ago, pianokeyjoe said: ah cara! Tive o mesmo problema com meu MT500 e consertei e agora, já faz anos (2018), esqueci o que consertei nele haha! Eu sei que era algum componente simples e não um transistor ou IC. Eu acho que era um diodo, pois é fácil de verificar enquanto está no circuito e eles tendem a agir como um fusível que pode queimar facilmente quando você mexe nos circuitos errados tentando dobrar o circuito haha.. Oh meu dia de flexão de circuito : D. O outro poderia muito bem SER um resistor, mas supondo que você nem o proprietário anterior tenham feito qualquer flexão de circuito e a situação da bateria esteja boa, então você precisa verificar os cabos de fita que vão entre a placa principal (placa maior) e a placa amplificadora de POWER/áudio (a placa com seu conector de alimentação DC e conectores de áudio). Pode ser também que alguém tenha tentado usar uma fonte de alimentação central positiva de 9 VCC em vez da fonte de alimentação central negativa correta, mas mais difícil de encontrar, de 7,5 V CC, e isso fez com que um diodo aparecesse entre o IC do amplificador e o gerador de tom. disso eu acho que é isso! Verifique a seção do amplificador. Eu ouço o zumbido do próprio casio, e é diferente a cada som que você seleciona, então sim, está tudo bem com o lado lógico das coisas, você precisa se concentrar agora no amplificador de áudio e testar os resistores e principalmente os diodos ao redor que esses diodos seriam usados para evitar feedback de áudio e retroalimentação de tensão entre chips IC, etc. Você está quase lá, meu amigo! Hi, thanks for taking the time to respond! I did tests with the diodes here to detect any defects, also with the flat cable that connects to the main board, and there is no problem between them, I did a continuity test on the cable from one side to the other, and everything appears to be fine. , apart from the fact that the keyboard melody part doesn't work haha, but let's try other possibilities! Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 15 Author Share Posted January 15 (edited) Mais um vídeo mostrando o que realmente acontece com ele, com ritmos e algumas melodias mortas Edited January 15 by Riva Lima Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted January 27 Author Share Posted January 27 Guys, I got the service manual, I'm posting it for all... https://drive.google.com/file/d/1wrsjkiLiFo4w-gsI-i6DkahMg4AgkZc0/view?usp=sharing Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted February 26 Author Share Posted February 26 Finally solved! The problem is with the 'Sample Hold' chip... I just changed it and it's back to normal. To everyone who tried to help, thank you very much, and I hope that the solution will be a reference for someone who goes through this one day. Video abaixo 1 Quote Link to comment Share on other sites More sharing options...
Riva Lima Posted February 26 Author Share Posted February 26 Quote Link to comment Share on other sites More sharing options...
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