DIMITRIS73GR Posted March 10, 2020 Share Posted March 10, 2020 Hello, I own a casioctk-691 that was working fine but suddenly stopped working.When I press power button the LCD goes ON but on screen shows something like I press a lot of keys/buttons at the same time,some letters are half.Also none of the keyboard buttons and keybed keys working.No sound at all.It looks like cannot boot or load the firmware to continue.Also I cannot turn it off from power button and I have to unplug the ac/dc power plug..The 9v adaptor is fine and also I used another bench adaptor with the same results.With batteries same result also. I disassembled the keyboard.The power supply board is fine.All dc voltage/capacitors/diodes according the service manual are ok.The cpu board gets all the 5v,9v,3.3v power..I found only that 1 of 2 Vram ics getting very hot quicly.If Vram is faulty IC can this be the reason for no booting or Not?..I tried the factory reset but because buttons not working nothing happens..I sent message to CASIO for a spare pcb but with no luck..It is my favorite keyboard and I will be very glad if someone with knoledge can help me or any ideas? Sorry for my long message, Thanks, Dimitris. 😊 Quote Link to comment Share on other sites More sharing options...
Jokeyman123 Posted March 10, 2020 Share Posted March 10, 2020 I don't think those RAM chips should be running hot, this is not typical. Did you check voltage going to those pins power-usually one of the pins on the ends if these are dual-inline package ICs. If the voltages there are normal-should be 12v or 5V depending on the chip logic, I think it should 5. Most other pins, without knwing the exact chip, will be ground-no voltage, Others would (typically) be lower voltage than the source voltage. And if the Vram is shorting out-yes definitely would cause it to not boot. You might have luck checking websites that sell spare parts for Casios. I know of three-Keyboard Kountry, Casio Junkyard and Fullcompass-you might want to check eBay which also has a few listings for Casio mainboards-there are some around, especially for the older Casios. Are the chips socketed? I would guess not, but you might be able to source a chip if these are. I have managed to find some pretty oddball ICs if you google around the web. Hope you manage this successfully! Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted March 10, 2020 Author Share Posted March 10, 2020 Thank you very very much for your help...These ics are identical.The one is not hot,the other is really very hot.The voltage on the ics is fine..You said if vram is shorting definetely would cause to no boot..That makes me very happy because I found the ic on ebay (its very common) and i have the knowledge to desolder and solder the new ic with hot air gun.. 1 Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted March 10, 2020 Author Share Posted March 10, 2020 (edited) voltage goes to ic is 3.3v. Edited March 10, 2020 by DIMITRIS73GR add some explanation Quote Link to comment Share on other sites More sharing options...
Jokeyman123 Posted March 10, 2020 Share Posted March 10, 2020 From your schematics-I think you have this already? Just in case. Definitely could be a major shorted chip. there might be other peripheral damage, if this IC has shorted anything else. Are any neighboring components running hot-excluding of course the power ICs? How does the main CPU feel? Could be a little warm, but that would typically be OK. Shouldn't be too hot. I found 5 casio mainboardson e*&&^%ay but not specifically for the 691, but close, if this repair doesn't work. Casio CTK691 service manual.pdf Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted March 10, 2020 Author Share Posted March 10, 2020 Thank you for your help...All other ics are not hot in the board.The cpu is almost cold just a very little warm.The only hot ic is a regulator wich is normal to get hot.It has a heatsink and the output voltages are fine.. If this repair does not work how to use another mainboard?..Is ti possible?..I think only ctk-900 is identical but I cannot find that either.. I visited the casio unkyard but no spaares fro my model... Quote Link to comment Share on other sites More sharing options...
Jokeyman123 Posted March 11, 2020 Share Posted March 11, 2020 I'll keep my Google eyes open for you too. I think you would need as close to an identical match as possible. Try the new chip first, might be all you need to do. Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted March 11, 2020 Author Share Posted March 11, 2020 Thank you very much for your interest and help...I will replace the ic and I will inform you for the results...Have a good day!!🙂👍 Quote Link to comment Share on other sites More sharing options...
Jokeyman123 Posted March 11, 2020 Share Posted March 11, 2020 You are welcome-I do quite a bit of repairs myself, interested to see how you do. Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted April 23, 2020 Author Share Posted April 23, 2020 Hello,how are you?.. I received the vram ic i changed it but nothing...still the same...I think this is the end of my keyboard...the m1am main board cost 228 us$ so I will stop repairing it.. Quote Link to comment Share on other sites More sharing options...
IanB Posted April 23, 2020 Share Posted April 23, 2020 I think the CPU is not running. Have you got an oscilloscope or a multimeter that can test frequencies? Are you able to run the diagnostic program by holding down Cursor Up and Cursor Down when pressing the Power button to power on? Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted April 23, 2020 Author Share Posted April 23, 2020 Hi,I tried the diagnostic program,no respond.I have the correct voltage on cpu ic but I dont have an oscilloscope. The only button that working is the power on.If I try to power off from the same button nothing happens...You are right I think also is CPU or bootloader. Quote Link to comment Share on other sites More sharing options...
IanB Posted April 26, 2020 Share Posted April 26, 2020 Hi Dimitri, sorry I missed your reply as the notification went in my spam folder. I think the problem is this needs technical facilities like test gear to figure out what the problem is. Unfortunately without that it could be pretty much anything wrong. The warm RAM chip makes me wonder if the CPU is permanently stuck on a memory access, overheating the chip. I take it your test meter doesn't have a frequency range? Quote Link to comment Share on other sites More sharing options...
HELVETIA Posted April 26, 2020 Share Posted April 26, 2020 On 4/23/2020 at 5:07 PM, DIMITRIS73GR said: Hello,how are you?.. I received the vram ic i changed it but nothing...still the same...I think this is the end of my keyboard...the m1am main board cost 228 us$ so I will stop repairing it.. Your sure the new vram was new and not defective too ? I bought some chips from ebay in the past and they where just like death lol Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted April 27, 2020 Author Share Posted April 27, 2020 On 4/26/2020 at 4:32 PM, IanB said: Hi Dimitri, sorry I missed your reply as the notification went in my spam folder. I think the problem is this needs technical facilities like test gear to figure out what the problem is. Unfortunately without that it could be pretty much anything wrong. The warm RAM chip makes me wonder if the CPU is permanently stuck on a memory access, overheating the chip. I take it your test meter doesn't have a frequency range? No,my test meter is simple and doesnt have frequency meter...Thanks for your help..I am searching for the main board on the internet...I hope one day I ll find one to replace the defective board... Quote Link to comment Share on other sites More sharing options...
DIMITRIS73GR Posted April 27, 2020 Author Share Posted April 27, 2020 23 hours ago, HELVETIA said: Your sure the new vram was new and not defective too ? I bought some chips from ebay in the past and they where just like death lol Hello,the ICs were brand new.I ordered 2 of them and tried both... 1 Quote Link to comment Share on other sites More sharing options...
IanB Posted April 27, 2020 Share Posted April 27, 2020 Okay, no harm in trying some things. On board MA1M, find IC6 and measure the DC voltages on all the pins, and tell me what you get. Also, transistor Q2, what are the voltages on the 3 pins and also at the end of R35 nearest to Q2. With the board the right way up so you can read the writing correctly, that's the left side. IC6 is below the left corner of the big IC. Quote Link to comment Share on other sites More sharing options...
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