Rookierafa

Hi IanB I will do it when I return home I am a traveler worker, so I don't have the Casiotone with me now. As soon as I return I will do the experience and post the outcomes. Thank you for the advise.

Hello again. Hope everybody had a nice Easter, I am still in digestion mode. Today I disconnected and removed the main board from the Casiotone to check it better. I looked into the NJM4558 Op Amps datasheet and saw an YouTube video on how to use the multimeter to check Op Amps. I didn't remove them from the board, so I don't know if the results help in anyway to determine the problem or to narrow the extension of it. I made a draw with the 4 NJM4558D chips and respective reads. https://imgur.com/gallery/YR7zTTb

I whish you all a good Easter with your families, and thank you again for keeping helping me on this adventure to repair the Casiotone. I already checked for visible defects, found a capacitor with bad soldering bed and repaired it, but the power still stops somewhere. Made a continuity test in the main board for the ground rail and everything is grounded. Started to check the negative rail, but when arrives to the main board it splits in different directions and since the board is big I loose myself some times. I looked into the schematic and found that some transistors are labeled with "base, emitter and collector" but there are 3 of them that are labeled with "ground, supply and drain". I suppose this mean some difference exists between them. Can anybody enlighten me? Anyway I restarted to measure some stuff and found that the negative rail have power in some places on the main board, I found -15V on the connector with the Yellow/20pin cable and it is feeding pin 1 and 3 of the STK020 power amp and have 2 caps connected on the negative side to the ground. But the connector with the brown/19pin cable doesn't show values is just 0V. The first components I found in the path are some resistors and 2 transistors T08 and T27. And that's it. I am still waiting for a component tester I ordered, maybe next week is here. And I hope I can count with your help to figure it out because I don't have enough knowledge or experience to do it by myself.

Hi IanB. All the fuses are OK. After detailed examination, I decided to repair some traces that where dubious around the 7815. The result is not the prettiest but it worked, finally I got readings: Pin20/yellow = -15.18V Pin19/brown = -15.22V I get the same readings in the tip of the cables that feed the main board so they have continuity. But everytime I reconnect the cables to the main board, brown and yellow cable return to 0V, and no sound. I checked again and one of the op amp is reading +15 in both sides but the other is reading +15 in one side and in the other is oscillating near 0V and very small values.

Hi! Thank you in advance for helping. With all the cables for the main board disconnected. Measuring 7915: center pin = 0.08V (approx) right pin = 0.00V left pin = 0.00V Measuring the fuses: - VCC gives -27.8V +VCC gives +27.4V +VA/ +VDD +15.6V -VA -15.9V The 7915 is bolted directly on the PCB, no metal touching it. Measuring point 19/brown reads 0.00V. https://imgur.com/gallery/zsvfbwv https://imgur.com/gallery/H8g4ddD

In the pin 19/brown and in the pin 20/yellow the reading is 0V.

Hi all. I checked the main board and found that near the Power Amp there is +15V and -15V, but when I measured the op amps I found out that I have +15 V in both sides, pin4 and pin 8. I think the circuit need´s one to be positive and another one to be negative. Anybody more experienced can tell me how this is achieved or if this gives a better clue of what maybe is causing the synth to go mute?

Thank you for the info. Still trying to find the faulty part. I re-solder the transistor and the high pitch noise vanished. In any case I am still just getting very faint rhythm and melody noise.

Hi! I am trying to fix a Casiotone Ct401 for a friend. He complained that the keyboard started smoking and stop producing sound, it was disconnected and stored until now. Since we are in an area where audio tech´s are not available, and send this to a distant technician is economically unviable, because of the low commercial value of the keyboard, he asked me if I could try to fix it. And because I have some spare time a accepted looking at this as an opportunity to learn something new and expand my little electronic knowledge. I looked online for people with similar problems with this Casiotone models and found that usually it is a paper cap supressor in the power supply module that usually cause this issue and found that most of them solved the problem just changing it. I examine the module and that it was the burned cap ! https://imgur.com/4vpcaD1 https://imgur.com/S1WxpVt I started rubbing my hands with joy, it was going to be an easy solution. So I thought that although the paper caps are unreliable, my friend would be ok maintaining the originality of the object. https://imgur.com/IoYWmj8 https://imgur.com/MS6SMZ5 I assembled everything to test it and, nothing happened, still no sound. Then I tried to troubleshoot basic stuff like: Speaker- ok Nothing connected or stuck to the headphone line, cleaned, re-solder pins.- (started to ear very low almost unperceptive sound of the accompaniment rhythm and melody sounds, but still no proper sound) Volume Pot resistance (continuity of the cables also)- ok Visual inspection -no cracks anywhere in solders or boards Key Bed cleaned and checked - ok Key Bed ribbon cable continuity - ok One dirty 22u100V Cap from the power supply removed and checked - Ok Cables from power supply to mainboard continuity- Ok So after this I got the Service Manual, and measured the points, and found out something that I am fighting to understand because of my rookieness. I found that the +VCC voltages reads ok in the main board it gets +15 and in the power supply side reads +25 , the 5+ V in the main board reads ok, the ground pins reads 0 everywhere, but every single place where it is supposed to read -15V in the ,ain board reads 0 nd in the -VCC in Power supple board, reads 0 too. https://drive.google.com/file/d/1oND9ugvzNN9W4g83hsgiObp5lFSWdhh4/view?usp=drive_link https://imgur.com/SdWYmyH https://imgur.com/EeMtHD7 After this I started to suspect of the transistor 79M15, downloaded the datasheet and found out that this transistor output is -15V. Again I thought, Voilá! https://imgur.com/HORbGy2 But No no! I ordered a spare one and changed it, and measured, and finally I have -25 in -VCC in the power supply board but nothing in -15 point in the main board. This piece o s$%# still doesn´t sing, just started to make a high pitch noise, and with headphones I can ear a little bit better the accompaniment rhythm but nothing close to the supposed sound. https://imgur.com/rjj0jEX And that´s it I am stuck! Can anybody, please, help me to find out what is going wrong with this? I still thought maybe it can be the STK020 Power amplifier is bad, but I don´t want to order more stuff without being certain of what it is happening with this. Thanks in advance