CasioForest Posted June 17, 2022 Share Posted June 17, 2022 (edited) hello everyone, long time listener but a first time caller. My beloved casio tone m10 has been giving me issue in that it isn’t producing any sounds anymore. It turns on with both a battery and power supply, and the volume control works and the floor noise is audible when the volume is turned all the way up (this hum is affected a bit when keys are depressed), but no actual sound as far as the 4 settings go. the vibrato switch doesn’t seem to affect the noise floor hum at all. So its safe to say its at least not the speaker as its amplifying fine and the problem persists through the outboard jack as well. I’m very very green with electronics and this is my first dive in diagnosing what specific component is giving me issue on the circuit. A visual noted some leaked battery evidence near the battery port but nothing that I could see on the traces or the circuit board. no obvious burned up components. There are what looks to be 'burn' marks on the top side of the circuit to the battery leak but nothing I could see in detriment to the underside traces. I couldn’t find a schematic or service manual, if anyone has either i'd be very much grateful. for the time being without, I started measuring the supply voltage for each of the following IC’s and transistors on the board with the following values. If i’m doing this wrong please stand me corrected. 2SK30 JFET=1.88V ????? 2SD400 NPN SILICON TRANSISTOR=5.30V TC40H004P HEX INVERTER=5.44V TC40H074P D-TYPE FLIPPY FLOPPY=5.48V 14049UB HEX INVERTER=5.30V 14049UB HEX INVERTER=5.30V D773G MAIN BRAIN=5.42V LA4120 AMP= (and I hope i'm measuring the right pins as I couldn't find a definitive data sheet . VCC+ on pin 1 and ground on 16, is this correct? if so, im not getting a reading. but if i go off the ground on pin 5 (if im assuming right), im getting 4.75V. what's weirder is that if i put my ground to the ground pin 8 on the 14049UB, the voltage for the la4120 reads out at 10.76V which seems high instinctively but then again im tripping my way through this and don't really know what I am doing ) S10L0025 (S10L0025C-2001 printing on component)=???? I couldn't find a data sheet for this little guy either I wasn’t able to get a measurement for the S10L0025 or the LA4120 as i couldn’t find a data sheet and didn’t want to risk probing about on an inline IC or one where I can’t make out the definitive polarity. If its safe to experiment with some deductive reasoning and the probe i’d love to get some kind of measurement to go off to help. I also wasn’t able to get a proper measurement for the 2SK30 Jfet as I’m not sure if i’m doing it correctly by measuring the voltage off the drain. Is this the correct approach to getting the voltage readings for that JFET? When I do try I get an increase in noise through the speaker when I probe the drain pin, and I do get a voltage reading of 1.88V. i’m not really sure where to go from here other than hoping this means that the chips are at least ok and the problem may be with one of the several electrolytic capacitors on the board. there are a number of diodes too that are not marked. could these be considered a viable suspect for what may be going wrong? could it be any of the resistors? How does one troubleshoot things further down to the very component if its not one of the chips? Thanks for any help folks, it would be amazing to get this up and running again to make some music with Edited June 17, 2022 by CasioForest 1 Quote Link to comment Share on other sites More sharing options...
IanB Posted June 17, 2022 Share Posted June 17, 2022 Hmm, okay. Can we have some photos of the PCB etc? First quick thing, when checking power voltages, don't use the ground pin of the IC as ground. Use some common ground reference point e.g. ground on the power supply or the negative terminal on the output jack. I see the LA4120 is a power amp, I can't find a pinout either (as of this posting) but it may be dual rail e.g. +5 and -5, hence your 10.76V. It probably isn't any standard position for the power pins. You should be able to trace the power connections to the rails though, by identifying the rails on the board (or we should be able to do it with photos). But the power amp sounds like it's working anyway so the problem would be elsewhere. It could just be a bad switch in the signal path, for instance. I Another possibility is the CMOS chips like the 4049s, one logic gate down could take out the signal. I wouldn't be surprised if it's one of those. The 773G is (I think) one of Casio's range of music LSIs, looking for info but can't find anything right now but it rings a bell. This is a small keyboard and I'm going to assume that the LSI puts out an analog signal that eventually reaches the amp via (probably) some other filtering circuitry but we don't know which pin that comes out of; a bare audio cable (shield to the keyboard's ground) could be used to find it and trace audio generally (the other ended plugged into an amplifier). I did find this company that says they have the service manual for download, they look legit to me but I've never used them https://www.samswebsite.com/en/photofact/details/index/id/31489 -but it is $23.00 to get it. If you go that route, I'd email them to check it's the right manual before ordering. My first guess is this will turn out to be one of the CMOS chips (the inverters or flip flops) but my first guesses are frequently wrong! Quote Link to comment Share on other sites More sharing options...
Brad Saucier Posted June 17, 2022 Share Posted June 17, 2022 8 hours ago, CasioForest said: Hello everyone, long time listener but a first time caller Welcome to the forums! Quote Link to comment Share on other sites More sharing options...
Chas Posted June 17, 2022 Share Posted June 17, 2022 I covered some of the hardware details in the first segment of Part 2 of my M10 Test & Review video (see below). There's also links in the video description to Robin Whittle's modification guide that contains a lot of technical info. Some of that might help guide you in fixing your M10? 1 Quote Link to comment Share on other sites More sharing options...
pianokeyjoe Posted June 18, 2022 Share Posted June 18, 2022 (edited) @CasioForest I read your post and I waited for the punchline and I got it.. Battery leak damage to the circuit board directly behind the battery compartment from what you added to your post. You are not going to diagnose components if battery alkali has already eaten through some circuit traces. As @IanBhas asked, we need you to take good close up pics of the circuit board in the areas where you SEE the damage in order to better help you. No schematic or manual is going to help this situation for now. DO NOT power the unit on again, until the battery leak damage is remedied and you have carefully cleaned off the battery acid(alkali)off the board inside. I was told baking soda and vinegar. Google the best option for you as I have tried both and at least for me I only had to use vinegar(white distilled) to clean my Yamaha PSS480 and that worked soo, mileage may vary. Simple fact, I buy Casios second hand at fleamarkets in Florida and the ONE thing I hate is when they left batteries in the darn things. That is the bane of my Casio existence.. batteries.. Cause they leak and ruin all the fun. BTW, I reread your post and seems you did quite a bit of troubleshooting already. Now you say you see burn marks on the component side of the PCB? Near WHAT components? Also your voltage readings for the most part are correct for a 6VDC powered instrument(Casio PT1,VL1 are 6VDC). I am betting you have a eaten trace or bad discrete component like one of the resistors or diodes. But without pics it is only speculation as this seems to be a situation that DOES show visible signs of distress, it is just now a matter of getting more eyes on the prize to help ya. I say a eaten trace only because some traces LOOK like they are ok but are indeed slightly darker shade of green or black gray in color.. indeed very close and careful inspection will reveal something. Edited June 18, 2022 by pianokeyjoe adding more info. 1 Quote Link to comment Share on other sites More sharing options...
CasioForest Posted June 19, 2022 Author Share Posted June 19, 2022 (edited) Hi everyone and thanks a bunch for taking the time with your responses. They were very much helpful and i've already gone about cleaning the remaining alkaline residue off the case (thanks a bunch @pianokeyjoe)(after the fact when these photos were taken). Apologies for my late reply as it took me a bit to figure out how to get a photo posted here. You can see the residue and the 'burn' marks on the top side of the PCB. Fortunately, they seem very nominal and most of the spill occurred on the casing and doesn't seem to have affected any of the components or traces to the underside. One thing I did notice is that when trying to get voltages off of the 14049UB's, that it was difficult as it seemed some of the pins were rusting over a bit. the voltage was either real low or jumping about, i had to scratch away some of this residue to get a constant reading at around 5.5V. Figured I would mention that but it doesn't appear that the battery explosion affected the actual PCB, and from what I can remember, this unit was functioning after the rupture and removal of the damaged batteries. memory be hazy these days though. thanks a bunch @IanB for your reply, that does now make sense if my issue is with one of those 4049's. They do measure voltage though, but is it possible to still be damaged and measure a voltage? Sorry for the beginner questions. And thanks for the link to the service manual, if I keep on hitting a wall and grab it ill be sure to get a schematic up here if that is ok for the archives. Reckon it would be helpful for other folks in this situation. @Chasyour video is what eventually led me here lol! Your video(s) are great and were a wealth of knowledge and what made me dust off the m10 in the first place, realize it was dead, then somehow find this spot. Thanks a bunch, it was the only place I could find a clear gut shot before I eventually opened mine up. I'm going to go about remeasuring the voltages just for the sake of good practice, thanks again @IanB for showing me the error in my ways in where im putting my grounds. Gonna see where I can source those pins too for the LA4120 and see if things differ from the original voltages i pulled. If its not one of those chips and it may be a discreet component, how does one zero in on it? I was looking into using an audio probe but not sure where to start on the circuit just yet. Would that be a good approach to take to figure out whats wrong? Thanks again everyone for the help : ) Edited June 19, 2022 by CasioForest 2 Quote Link to comment Share on other sites More sharing options...
IanB Posted June 19, 2022 Share Posted June 19, 2022 @CasioForest The fact there are voltages on the power supply pins of an IC doesn't mean it is working; neither does the presence of voltages on the output pins of the internal gates. The output may be incorrect, or stuck at high or low voltage. Often a single gate can fail (e.g. one inverter out of the six in a hex inverter). They are commonly available as replacements fortunately, and cheap. Observe anti-static precautions as they are CMOS chips. Example here https://uk.farnell.com/texas-instruments/cd4049ube/inverting-buffer-hex-4000-cmos/dp/3119255 (it can be a bit tricky searching for part numbers as they tend to have extra letters; in this example note the CD4049UBE. Rusty pins isn't a good sign but that doesn't mean they are at fault also. I'm presuming you don't have an oscilloscope? Quote Link to comment Share on other sites More sharing options...
pianokeyjoe Posted June 20, 2022 Share Posted June 20, 2022 Thankyou for the mention and for the big pictures! Ok, I cringed when I saw the top of the PCM and that big section of the keybed with rust.. that is battery acid rust. and then there is the punchline... the Power Amp IC chip which has brown discoloration all over the top.. That is the LA4120? I think that is the bad componant.. The top of that LOOKS burnt.. I mean that top label is silver white in most normal cases of these Casios. That usually get a heatsink on some cases too. Yours is burnt, and that is where you get your audio output from. So it is NOT a logic IC that is out cause you said you could hear like buzzing when you pressed keys no? Like there is a hum that changes with key presses.. You seriously need to look at the schematic and check the amp INPUT pin with something that can do audio like the mic input of a cassette recorder or your computer(set the mic input to ON or to monitor)and take the other end of the 3.5mm cable stripped and hook the ground to ground on the Casio, and the live or hot mic input lead to the amplifier INPUT pin and then play the keyboard keys. Make sure to turn the mic level up to midway and the keyboard to max volume. Mmm.. btw, Have you checked the volume control to see if it is defective? That would be an even easier check. You short out the pins of the volume where the max volume would be(find the common on the POT and use a wire to touch from the common(wiper), to either of the other pins on the POT, while pressing keys or using a rubber dome to activate a key whilst it is apart). USE the 6VDC adapter to power it do not use batteries. I fixed a Yamaha PSR11 this way. It has a defective volume slider but I have none to replace so I just shorted the volume to MAX. Try those things and see. I doubt there is a LA4120 for sale new now but ya never know. 1 Quote Link to comment Share on other sites More sharing options...
Chas Posted June 21, 2022 Share Posted June 21, 2022 On 6/19/2022 at 9:45 PM, pianokeyjoe said: T. I doubt there is a LA4120 for sale new now but ya never know. A quick Google search and I found a couple of sellers with new LA4120 chips for sale: https://www.ecrater.com/p/29112806/sanyo-la4120-2-channel-af-power https://www.ebay.com/itm/371237825471?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=PkjcM4faSgC&sssrc=2349624&ssuid=Y2Gbk031Qm2&var=&widget_ver=artemis&media=COPY 1 Quote Link to comment Share on other sites More sharing options...
IanB Posted June 21, 2022 Share Posted June 21, 2022 From the picture, I don't see damage to the LA4120 itself, though the top has clearly been dunked in gunk. It looks like there's metal on top, a small heatsink? This thing has a line out, right? That should be unaffected by the LA chip which is the power amp? Quote Link to comment Share on other sites More sharing options...
CYBERYOGI =CO=Windler Posted July 7, 2022 Share Posted July 7, 2022 (edited) Power amp chips can oxidize also without overheat. If it turns hot (burns your finger) when turned on, then it is toast (this will happen if anybody used a power supply with wrong polarity). If not, battery acid does nasty things (in worst case ate itself through the package and destroyed that chip from inside) and definitely can discolour metal this way. Particularly measure continuity of PCB traces with a DMM. If any traces have dark spots under the green coating, they are likely corroded and need to be patched with solder and a piece of thin copper wire (e.g. one individual fiber of a wick cable). The Robin Whittle text has thoroughly analyzed the digital part of this hardware. Edited July 7, 2022 by CYBERYOGI =CO=Windler 1 Quote Link to comment Share on other sites More sharing options...
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