Help with Casio keyboard not working

[LJ89]

Also should I go ahead and desolder PIN 11 of 4127? and if so.. what should I look for after I desolder PIN 11..

NO . . . . no need to float / desolder pin 11 that was being related to your initially only finding 1.8 VDC on it.
Your retest has now shown that the 4117 is NOT severely loading down your input power. . .and is actualluy pulling ~
~ 300 mw.

BATTERY POWERED ON:

PIN 1 : 9.04V
PIN 2 : 8.36V

BATTERY POWERED OFF:

PIN 1 : 9.25V

Can you now do my earlier test of going into AC metering mode in 1 VAC or less range and measure with meter neg to ground and red meter lead to
4127 and replicate the earlier procedure found in post # 24. Repetitively key in and then stop a note and the meter should respond accordingly.
Therewith, we are wanting to know if there actually is a note being created back at the uPs output and then showing up at the audio input of the 4127.
If being so, we will then have to further evaluate the units 4127 situation.

Sir I have completed your test of pressing a key and measuring the voltage.

keyboard was battery powered, turned ON, volume at max position.

With my black lead on ground and my red lead on LA4127 PIN 6 there was no voltage change when key was pressed or not. It stayed at 0 VAC

With my black lead on ground and my red lead on LA4127 PIN 15 there was no voltage change when key was pressed or not. It stayed at 0 VAC.

I wasn't sure if I was selecting the range properly so I've attached a picture.

I also did the same test of having someone press a key while measuring the voltage on DC mode just to see if it made a difference and it did not.... both pin 6 and pin 15 stayed at 0vdc, regardless if a key was pressed or not...

Although there definitely was a lot of audible static coming from the speakers when my red lead was on 6 or 15 I noted.


I also did the test with my black lead on pin5 and than tested pin 6 and pin 15 with someone pressing the keys, no voltage was measured at all. I did both AC and DC....

But my conclusion was that there was no change when the key was being pressed... all the reading were at 0 volts....

I've attached a picture and maybe let me know if my meter was on the correct setting.

 

[vbplayer]

LJ89 ..... did you ever get any further responses to resolve your problem?

I have a very similar situation with trying to fix my Casio CT-670.

Per Harold Kapp's recommendation in Post #8, I saw where you took measures across pins on the CA5668 Voltage Regular IC and recorded those measurements in Post #19. But, I didn't see that the voltage on pin 6 was close to 5V DC. This is concerning, which is my issue also.

I would like to try to help you solve your problem, while trying to see if I can solve my problem too. Perhaps you have found a solution outside this forum or have just given up. Maybe I should start a new tread, any advice Harold as a Moderator?

 

[H2814D]

I noticed this thread did not come to a successful conclusion. In looking at post #33, the solder connection above the two white wires near the upside down "B" looks odd to me. Anyone agree? I do remember the OP saying that he checked every solder connection though.

 

[LJ89]

LJ89 ..... did you ever get any further responses to resolve your problem?

I have a very similar situation with trying to fix my Casio CT-670.

Per Harold Kapp's recommendation in Post #8, I saw where you took measures across pins on the CA5668 Voltage Regular IC and recorded those measurements in Post #19. But, I didn't see that the voltage on pin 6 was close to 5V DC. This is concerning, which is my issue also.

I would like to try to help you solve your problem, while trying to see if I can solve my problem too. Perhaps you have found a solution outside this forum or have just given up. Maybe I should start a new tread, any advice Harold as a Moderator?

Hi there,

I have not fixed the issue, I ended up just ordering a replacement CA5668 and LA4127, I'm just waiting them to come over on a boat from China.

I kind of gave up and figured I'd just try that, plus my electronics skills are pretty non existent lol.

Il let you know if that does anything.

Sorry wish I could help more.

 

[LJ89]

I noticed this thread did not come to a successful conclusion. In looking at post #33, the solder connection above the two white wires near the upside down "B" looks odd to me. Anyone agree? I do remember the OP saying that he checked every solder connection though.

Yes you are right it does it quite questionable, when I get some time I will examine it further and resolder it.

Thanks for noticing that!

 

[vbplayer]

LJ89..... thanks for the response. I am going to throw out a lot of information on what I have done below. I don't want to overshadow your issue, but I think we are on a very similar (if not same) path. I also do not want to confuse the issue, so if you have any confusion on what I am saying (or terms I am using), please ask. I want to be part of the solution, not part of the problem.

Yes LJ89, I think it might be a good idea to try replacing CA5668 (or LA5668 as the same). I tried replacing this IC as pin #6 was reading only 2.14V DC. But, after that replacement, I still had low voltage on this pin with the new voltage regulator. I tested the 1st IC (i.e. the one I replaced) by itself and pin #6 read 0V DC (like the IC was damaged). I just don't want you to go down the same path I have LJ89 and start destroying voltage regulators.

I have been trying to understand if there is some circuitry on this VD output (like resistors or capacitors) that could be drawing down the expected 5V DC. I have desoldered pin #6 (on the new voltage regulator) from the PCB to isolate this output from other circuitry and now it reads 0V DC (like this IC is now damaged too). I have one more new voltage regulator IC (which I checked for proper 5V DC on pin #6 in an isolated environment off the PCB), but am reluctant to solder it into the PCB for fear I will just damage this IC too.

Are there any thoughts from anyone on this possibility (of other components damaging the voltage regulator) and what I should do to check for other bad components (following the pin #6 VD output)? Unfortunately, I don't have a capacitor meter right now (looking into getting one, but it seems like all of them have some issue or another, and I cannot afford a Fluke).

I also saw in Post #10 from 73's de Edd that the Vcc max voltage for LA4127 (power audio amplifier) is 11V DC. My AC power supply is putting out 11.28V DC to pin #11 of this amplifier (when the keyboard is switched ON). I am using the original AD-5 power supply I got with the CT-670 keyboard. Sound like this is too much supply voltage for this amplifier IC. Could the AD-5 power supply be the root of all my problems (i.e. can these wall warts actually go bad and produce MORE voltage)? I guess like LJ89, I could go to a set of 1.5V D batteries (or a mix of D & C batteries) to eliminate the wall wart.

 

[LJ89]

LJ89..... thanks for the response. I am going to throw out a lot of information on what I have done below. I don't want to overshadow your issue, but I think we are on a very similar (if not same) path. I also do not want to confuse the issue, so if you have any confusion on what I am saying (or terms I am using), please ask. I want to be part of the solution, not part of the problem.

Yes LJ89, I think it might be a good idea to try replacing CA5668 (or LA5668 as the same). I tried replacing this IC as pin #6 was reading only 2.14V DC. But, after that replacement, I still had low voltage on this pin with the new voltage regulator. I tested the 1st IC (i.e. the one I replaced) by itself and pin #6 read 0V DC (like the IC was damaged). I just don't want you to go down the same path I have LJ89 and start destroying voltage regulators.

I have been trying to understand if there is some circuitry on this VD output (like resistors or capacitors) that could be drawing down the expected 5V DC. I have desoldered pin #6 (on the new voltage regulator) from the PCB to isolate this output from other circuitry and now it reads 0V DC (like this IC is now damaged too). I have one more new voltage regulator IC (which I checked for proper 5V DC on pin #6 in an isolated environment off the PCB), but am reluctant to solder it into the PCB for fear I will just damage this IC too.

Are there any thoughts from anyone on this possibility (of other components damaging the voltage regulator) and what I should do to check for other bad components (following the pin #6 VD output)? Unfortunately, I don't have a capacitor meter right now (looking into getting one, but it seems like all of them have some issue or another, and I cannot afford a Fluke).

I also saw in Post #10 from 73's de Edd that the Vcc max voltage for LA4127 (power audio amplifier) is 11V DC. My AC power supply is putting out 11.28V DC to pin #11 of this amplifier (when the keyboard is switched ON). I am using the original AD-5 power supply I got with the CT-670 keyboard. Sound like this is too much supply voltage for this amplifier IC. Could the AD-5 power supply be the root of all my problems (i.e. can these wall warts actually go bad and produce MORE voltage)? I guess like LJ89, I could go to a set of 1.5V D batteries (or a mix of D & C batteries) to eliminate the wall wart.

Hey vbplayer,

So if I understand correctly something on that board is damaging your CA5668 voltage regulator. And it sounds like it could be due to bad capacitors. Is it possible to just change all the capacitors that are in line with that voltage regulator? I know this is a shotgun approach... and probably the right thing to do is to get a capacitor testing tool... but it sounds like that's expensive.

Is there anything else besides capacitors that could be causing damage to CA5668 voltage regulator ?

Thanks

Lj89

 

[vbplayer]

LJ89....... the questions you have are really the same questions I have. I don't know if there are other components in the circuitry following the CA5668 pin #6 output (VD @ ~5V DC) that could be causing the damage to this voltage regulator. I wasn't expecting you to have this answer and I don't have the answer either. I was hoping someone else in this forum (perhaps an expert) might be able to shed some light on this and help us figure out a way to troubleshoot this.

As for just replacing components (like capacitors) in a shotgun approach, that is an idea. I was hoping for a less invasive and more structured approach as I don't have any extra capacitors (of the right values) to swap in at this time.

As for capacitance meters, some of them are inexpensive (and cheap construction), but the reviews I read on them state: 1) many are delivered broken, 2) if they work on delivery, they break quickly, and/or 3) they are inaccurate. Plus, capacitance meters read the values of the capacitor to verify they are within tolerance. These meters cannot be used for "in-circuit" testing (i.e. you must remove the capacitor from the PCB), discharge the capacitor (so you don't damage your meter), then connect the test leads to the capacitor to get the value. If you want to do "in-circuit" testing of capacitors, an ESR Capacitance meter is needed from my understanding. You can do an internet search on this if you want to learn more about how an ESR meter works.

 

[LJ89]

LJ89....... the questions you have are really the same questions I have. I don't know if there are other components in the circuitry following the CA5668 pin #6 output (VD @ ~5V DC) that could be causing the damage to this voltage regulator. I wasn't expecting you to have this answer and I don't have the answer either. I was hoping someone else in this forum (perhaps an expert) might be able to shed some light on this and help us figure out a way to troubleshoot this.

As for just replacing components (like capacitors) in a shotgun approach, that is an idea. I was hoping for a less invasive and more structured approach as I don't have any extra capacitors (of the right values) to swap in at this time.

As for capacitance meters, some of them are inexpensive (and cheap construction), but the reviews I read on them state: 1) many are delivered broken, 2) if they work on delivery, they break quickly, and/or 3) they are inaccurate. Plus, capacitance meters read the values of the capacitor to verify they are within tolerance. These meters cannot be used for "in-circuit" testing (i.e. you must remove the capacitor from the PCB), discharge the capacitor (so you don't damage your meter), then connect the test leads to the capacitor to get the value. If you want to do "in-circuit" testing of capacitors, an ESR Capacitance meter is needed from my understanding. You can do an internet search on this if you want to learn more about how an ESR meter works.

I understand, hopefully we can both get an answer and fix our keyboards!

I found this on YouTube, could our problem be similar to this? And how does he find the " short circuit " so quick?

Let me know what you think.

Thanks

Lj89

 

[vbplayer]

It's possible, but with my little experience, anything is possible at this point. I am learning as you are right now. I did attempt to check a few capacitors the way he did on my end, but they seemed to be OK (from what little I know so far). I tried to look at your circuit board layout from your pics in Post #1, but it's hard to determine the exact schematic from traces on one side of the board (green side) and components on the other side (brown side).

If you want to test capacitors the way this guy in the video does (for shorts), I can run you through that procedure. But, in order to know what capacitors are related to the pin #6 output of the voltage regulator, I will have to find a service manual for your Casio. I cannot remember if someone found that manual and put a link to it in this thread. I will look around.

Also, on your question as to how he finds it sooooo fast, I think he has a lot of experience doing this kind of debugging.

Another thing I want to mention is I screwed up on some terminology and want to correct myself so I don't add any further confusion. I used the term "VD" in several places in my previous posts. In looking at the pinout diagram for CA5668 in Post #32, "VD" is actually the output from pin #8 (which is the 5-volt supply to the Digital circuitry on the PCB(s). "VA" is the output from pin #6 (which is the 5-volt supply to the Analog circuitry on the PCB(s). I should have used "VA" wherever I used "VD". My bad.

 

[vbplayer]

I could not find a Service Manual for the CT-638. Bummer.

 

[LJ89]

It's possible, but with my little experience, anything is possible at this point. I am learning as you are right now. I did attempt to check a few capacitors the way he did on my end, but they seemed to be OK (from what little I know so far). I tried to look at your circuit board layout from your pics in Post #1, but it's hard to determine the exact schematic from traces on one side of the board (green side) and components on the other side (brown side).

If you want to test capacitors the way this guy in the video does (for shorts), I can run you through that procedure. But, in order to know what capacitors are related to the pin #6 output of the voltage regulator, I will have to find a service manual for your Casio. I cannot remember if someone found that manual and put a link to it in this thread. I will look around.

Also, on your question as to how he finds it sooooo fast, I think he has a lot of experience doing this kind of debugging.

Another thing I want to mention is I screwed up on some terminology and want to correct myself so I don't add any further confusion. I used the term "VD" in several places in my previous posts. In looking at the pinout diagram for CA5668 in Post #32, "VD" is actually the output from pin #8 (which is the 5-volt supply to the Digital circuitry on the PCB(s). "VA" is the output from pin #6 (which is the 5-volt supply to the Analog circuitry on the PCB(s). I should have used "VA" wherever I used "VD". My bad.

So if I follow the 'traces' from CA5668, that could lead me to what capacitors, resistors are in line with it? If I understand correctly, you will know what is connected to what.. Like a schematic , but this is just done visually?

Also if you don't mind, how do I go about testing for shorts like the guy does in the video. I watched him do it but I just don't fully grasp what he's actually doing.. I have a hard time understanding electronics :/ I think it has to do because it's something I can't actually see.

Thankyou

 

[vbplayer]

Since I couldn't find a service manual, I tried combining 2 of your images: 1) the component side of the board, and 2) the trace side of the board. It is a bit difficult to see everything because of the overlay. But, if you look closely and zoom in a lot, you can see how the components are connected to the traces. Don't know if this is useful, but it was sort of fun to see if I could actually create this. In order to upload this image, I had to greatly reduce the file size (from a 6.77MB PNG file to 825KB JPG file) probably due to some size constraint imposed by the forum. Hopefully, it will still be useful at a lower resolution.

As for your last post LJ89 (#52), the answer to your 1st question is 'yes, you will just need to follow the traces from component to component'. Hopefully, the image I provided will help with that. Without me going through my 'make-shift schematic' (i.e. my image) in detail, I cannot tell you every capacitor, resistor and other component that are tied to the pin #6 output of the voltage regulator (CA5668). But, I can see a 22Ω resistor on the output of pin #6 followed by the 6V220μF capacitor which goes to ground. So you could check these 2 components. The 22Ω resistor is located just below the CA5668 voltage regulator IC (near pin #10) and the 6V220μF capacitor is just to the left of that resistor.

Checking resistance (for resistors) and shorts/opens (on capacitors) are done with the power OFF (never with power ON as this will kill your meter). In fact, I would probably remove the AC plug from the keyboard (if you are using an AC wall wart) or at least one of the batteries (if you are using batteries in the battery compartment). This is also a good safety precaution to ensure you don't get zapped (even though this is fairly low power, but still good practice).

For the 22Ω resistor, set your multimeter to the lowest setting that is above 22Ω (it should be something like '200' or '2000' on your meter). Make sure you are setting the meter dial to ohms (Ω), not amps (A) or volts (DCV or ACV). You probably know this, but I am not sure exactly what experience you have with this stuff (no insult intended). With resistors, there is no polarity (i.e. + and - doesn't matter), so you can connect your test leads from your meter across the resistor leads in either direction. You should read something around 22Ω. The really important thing is that you don't read something close to 0Ω (meaning a short-circuit) or something up greater than 100Ω (meaning an open-circuit). If short or open-circuit is determined, removed the resistor from the PBC and checked it again off-board

For the 6V220μF capacitor, the first thing you ALWAYS want to do with any capacitor is DISCHARGE IT. This is something any of us can forget to do, but it will fry your meter.(whether you are using your multimeter to check continuity or a capacitance meter to check the capacitance value). We will be using your multimeter to check continuity (i.e. whether there is a short or open-circuit) and whether the capacitor charges or not. This continuity test (which is what the guy in the video was doing) does not by itself prove that a capacitor is perfectly good. But, it is a good start to checking them out quickly for problems. OK, back to DISCHARGING a capacitor. The easiest way to do this is to put some kind of metallic conductor across the capacitor leads (i.e. + and -). This can be done with a screw driver or even a bent paper clip (since this is low voltage). You DON'T want to do this in a high voltage situation (like a capacitor in a heat pump using 220V (as you could die - VERY DANGEROUS). Now that the capacitor is discharged, set your multimeter to the 'continuity' setting (which looks like a diode, i.e. a filled-in sideways triangle with a vertical line on one side). Now, figure out which side of the capacitor is the negative (-) side. This is indicated on your PCB by a '-' symbol inside a circle. There is a stripe drawn on the side of the electrolytic capacitor (6V220μF capacitor type). Connect the positive (+) lead of your multimeter to the + side of the capacitor and connect the negative (-) lead of your multimeter to the - side of the capacitor. You SHOULD see the number on your meter going up very quickly which means your capacitor is charging (eventually it will stop meaning it is fully charged, but you don't need to fully charge it). If you don't see this, there is something wrong with the capacitor. There are 2 things that can be wrong: 1) there is a short-circuit (indicated by a very low constant value, like 0 - 10), or 2) this is an open-circuit (indicated usually by a '1' on the left side of the meter or 'OL' displayed). Both of these things are major problems and the capacitor should be removed from the PBC and checked again off-board. To reiterate, ALWAYS discharge your capacitor before testing it (even if you are testing the same capacitor again).

I know I over-killed this explanation, but I just want to ensure it is clear and safe. Let me know what you find out and if you have any questions (which I will try to answer).

 

[LJ89]

Since I couldn't find a service manual, I tried combining 2 of your images: 1) the component side of the board, and 2) the trace side of the board. It is a bit difficult to see everything because of the overlay. But, if you look closely and zoom in a lot, you can see how the components are connected to the traces. Don't know if this is useful, but it was sort of fun to see if I could actually create this. In order to upload this image, I had to greatly reduce the file size (from a 6.77MB PNG file to 825KB JPG file) probably due to some size constraint imposed by the forum. Hopefully, it will still be useful at a lower resolution.

As for your last post LJ89 (#52), the answer to your 1st question is 'yes, you will just need to follow the traces from component to component'. Hopefully, the image I provided will help with that. Without me going through my 'make-shift schematic' (i.e. my image) in detail, I cannot tell you every capacitor, resistor and other component that are tied to the pin #6 output of the voltage regulator (CA5668). But, I can see a 22Ω resistor on the output of pin #6 followed by the 6V220μF capacitor which goes to ground. So you could check these 2 components. The 22Ω resistor is located just below the CA5668 voltage regulator IC (near pin #10) and the 6V220μF capacitor is just to the left of that resistor.

Checking resistance (for resistors) and shorts/opens (on capacitors) are done with the power OFF (never with power ON as this will kill your meter). In fact, I would probably remove the AC plug from the keyboard (if you are using an AC wall wart) or at least one of the batteries (if you are using batteries in the battery compartment). This is also a good safety precaution to ensure you don't get zapped (even though this is fairly low power, but still good practice).

For the 22Ω resistor, set your multimeter to the lowest setting that is above 22Ω (it should be something like '200' or '2000' on your meter). Make sure you are setting the meter dial to ohms (Ω), not amps (A) or volts (DCV or ACV). You probably know this, but I am not sure exactly what experience you have with this stuff (no insult intended). With resistors, there is no polarity (i.e. + and - doesn't matter), so you can connect your test leads from your meter across the resistor leads in either direction. You should read something around 22Ω. The really important thing is that you don't read something close to 0Ω (meaning a short-circuit) or something up greater than 100Ω (meaning an open-circuit). If short or open-circuit is determined, removed the resistor from the PBC and checked it again off-board

For the 6V220μF capacitor, the first thing you ALWAYS want to do with any capacitor is DISCHARGE IT. This is something any of us can forget to do, but it will fry your meter.(whether you are using your multimeter to check continuity or a capacitance meter to check the capacitance value). We will be using your multimeter to check continuity (i.e. whether there is a short or open-circuit) and whether the capacitor charges or not. This continuity test (which is what the guy in the video was doing) does not by itself prove that a capacitor is perfectly good. But, it is a good start to checking them out quickly for problems. OK, back to DISCHARGING a capacitor. The easiest way to do this is to put some kind of metallic conductor across the capacitor leads (i.e. + and -). This can be done with a screw driver or even a bent paper clip (since this is low voltage). You DON'T want to do this in a high voltage situation (like a capacitor in a heat pump using 220V (as you could die - VERY DANGEROUS). Now that the capacitor is discharged, set your multimeter to the 'continuity' setting (which looks like a diode, i.e. a filled-in sideways triangle with a vertical line on one side). Now, figure out which side of the capacitor is the negative (-) side. This is indicated on your PCB by a '-' symbol inside a circle. There is a stripe drawn on the side of the electrolytic capacitor (6V220μF capacitor type). Connect the positive (+) lead of your multimeter to the + side of the capacitor and connect the negative (-) lead of your multimeter to the - side of the capacitor. You SHOULD see the number on your meter going up very quickly which means your capacitor is charging (eventually it will stop meaning it is fully charged, but you don't need to fully charge it). If you don't see this, there is something wrong with the capacitor. There are 2 things that can be wrong: 1) there is a short-circuit (indicated by a very low constant value, like 0 - 10), or 2) this is an open-circuit (indicated usually by a '1' on the left side of the meter or 'OL' displayed). Both of these things are major problems and the capacitor should be removed from the PBC and checked again off-board. To reiterate, ALWAYS discharge your capacitor before testing it (even if you are testing the same capacitor again).

I know I over-killed this explanation, but I just want to ensure it is clear and safe. Let me know what you find out and if you have any questions (which I will try to answer).

Thank you very much for the detailed response, I really appreciate the time you took to make that schematic picture.

You made the whole thing very understandable and It actually makes sense now.

I will most definitely be checking that capacitor and resistor. I will report back with my findings.

Thank you so much

 

[73's de Edd]

Sir LJ89 . . . .

You know . . . . back when you were checking out the voltages from that regulator and power switching I.C., I don't see your voltage figures for pin 6 being given.
And that is a constant on power supply output for some of the digital circuitry of the unit.
What voltage are you reading on 6 . As we initially were worried about the voltage from pin 1 getting to the power Audio output I.C.
But, you were initially just measuring incorrectly and a corrected measuring procedure then came up with enough. .
So o o o o o o how much DC is now being on pin 6 . . . . . .expecting + FIVE'ish ?

73's de Edd . . . . .




.

 

[LJ89]

Since I couldn't find a service manual, I tried combining 2 of your images: 1) the component side of the board, and 2) the trace side of the board. It is a bit difficult to see everything because of the overlay. But, if you look closely and zoom in a lot, you can see how the components are connected to the traces. Don't know if this is useful, but it was sort of fun to see if I could actually create this. In order to upload this image, I had to greatly reduce the file size (from a 6.77MB PNG file to 825KB JPG file) probably due to some size constraint imposed by the forum. Hopefully, it will still be useful at a lower resolution.

As for your last post LJ89 (#52), the answer to your 1st question is 'yes, you will just need to follow the traces from component to component'. Hopefully, the image I provided will help with that. Without me going through my 'make-shift schematic' (i.e. my image) in detail, I cannot tell you every capacitor, resistor and other component that are tied to the pin #6 output of the voltage regulator (CA5668). But, I can see a 22Ω resistor on the output of pin #6 followed by the 6V220μF capacitor which goes to ground. So you could check these 2 components. The 22Ω resistor is located just below the CA5668 voltage regulator IC (near pin #10) and the 6V220μF capacitor is just to the left of that resistor.

Checking resistance (for resistors) and shorts/opens (on capacitors) are done with the power OFF (never with power ON as this will kill your meter). In fact, I would probably remove the AC plug from the keyboard (if you are using an AC wall wart) or at least one of the batteries (if you are using batteries in the battery compartment). This is also a good safety precaution to ensure you don't get zapped (even though this is fairly low power, but still good practice).

For the 22Ω resistor, set your multimeter to the lowest setting that is above 22Ω (it should be something like '200' or '2000' on your meter). Make sure you are setting the meter dial to ohms (Ω), not amps (A) or volts (DCV or ACV). You probably know this, but I am not sure exactly what experience you have with this stuff (no insult intended). With resistors, there is no polarity (i.e. + and - doesn't matter), so you can connect your test leads from your meter across the resistor leads in either direction. You should read something around 22Ω. The really important thing is that you don't read something close to 0Ω (meaning a short-circuit) or something up greater than 100Ω (meaning an open-circuit). If short or open-circuit is determined, removed the resistor from the PBC and checked it again off-board

For the 6V220μF capacitor, the first thing you ALWAYS want to do with any capacitor is DISCHARGE IT. This is something any of us can forget to do, but it will fry your meter.(whether you are using your multimeter to check continuity or a capacitance meter to check the capacitance value). We will be using your multimeter to check continuity (i.e. whether there is a short or open-circuit) and whether the capacitor charges or not. This continuity test (which is what the guy in the video was doing) does not by itself prove that a capacitor is perfectly good. But, it is a good start to checking them out quickly for problems. OK, back to DISCHARGING a capacitor. The easiest way to do this is to put some kind of metallic conductor across the capacitor leads (i.e. + and -). This can be done with a screw driver or even a bent paper clip (since this is low voltage). You DON'T want to do this in a high voltage situation (like a capacitor in a heat pump using 220V (as you could die - VERY DANGEROUS). Now that the capacitor is discharged, set your multimeter to the 'continuity' setting (which looks like a diode, i.e. a filled-in sideways triangle with a vertical line on one side). Now, figure out which side of the capacitor is the negative (-) side. This is indicated on your PCB by a '-' symbol inside a circle. There is a stripe drawn on the side of the electrolytic capacitor (6V220μF capacitor type). Connect the positive (+) lead of your multimeter to the + side of the capacitor and connect the negative (-) lead of your multimeter to the - side of the capacitor. You SHOULD see the number on your meter going up very quickly which means your capacitor is charging (eventually it will stop meaning it is fully charged, but you don't need to fully charge it). If you don't see this, there is something wrong with the capacitor. There are 2 things that can be wrong: 1) there is a short-circuit (indicated by a very low constant value, like 0 - 10), or 2) this is an open-circuit (indicated usually by a '1' on the left side of the meter or 'OL' displayed). Both of these things are major problems and the capacitor should be removed from the PBC and checked again off-board. To reiterate, ALWAYS discharge your capacitor before testing it (even if you are testing the same capacitor again).

I know I over-killed this explanation, but I just want to ensure it is clear and safe. Let me know what you find out and if you have any questions (which I will try to answer).

Ok so I tested that resistor below and it read 22ohms ( just as it written down next to it on the pcb)

I tested the 6V220μF capacitor just left to that 22ohm resistor with the diode mode on the multi meter. It charged up to 0.998V... than it slowly fell down to 0.967V and stayed there.

So I found another capacitor with the same specs on the pcb written next to it (6V220μF) but this one charged to 2.1V.. and never went back down...

And than I found another capacitor on the board with the same specs (6V220μF) and it only charged it 0.98V.

So I'm not really sure if I can say anything definitely.

Maybe I will just follow the traces and see if I can see what is in line with PIN 6 and teat all those components and see if anything jumps out. I will be using the schematic you made. Thank you very much for gling out of your way to make that schematic and for the simple explanations you provided. It really helped me understand!

 

[LJ89]

Sir LJ89 . . . .

You know . . . . back when you were checking out the voltages from that regulator and power switching I.C., I don't see your voltage figures for pin 6 being given.
And that is a constant on power supply output for some of the digital circuitry of the unit.
What voltage are you reading on 6 . As we initially were worried about the voltage from pin 1 getting to the power Audio output I.C.
But, you were initially just measuring incorrectly and a corrected measuring procedure then came up with enough. .
So o o o o o o how much DC is now being on pin 6 . . . . . .expecting + FIVE'ish ?

73's de Edd . . . . .

View attachment 51281


.

Hello Sir,

The output of pin 6 of CA5668 is 1.248vdc. I tried both wallwart powered and battery powered. I had the red probe on pin 6 and I had the black probe on the ground plane ( star washer solder blobs on the side of the board)

 

[LJ89]

I noticed this thread did not come to a successful conclusion. In looking at post #33, the solder connection above the two white wires near the upside down "B" looks odd to me. Anyone agree? I do remember the OP saying that he checked every solder connection though.

I took a look at that solder joint and unfortunately it looks like it was just the angle of the photo. The solder joint is good. I appreciate you taking a look!

 

[73's de Edd]

Sir LJ89 . . . . .

OUR CONTINUANCE . . . . .

Now you are finding fault ! . . . . .
with that output pin 6 of the LA / CA5668, being now only at a 1.248 VDC level is being suggestive of it feeding out to a circuit and then encountering a short /or excessive loading on that branched off line, thereby loading down and pulling the +5V AVDD supply on down to that lower voatage level, instead of being the expected ~ 5VDC.

I magged up and then digitally enhanced one of your top board photos to give us the supplied reference and a relevant piecemeal researched schematic that agrees with your boards LC 7881C D/A converter , LM5218 dual op amp, used for filtering out of digital artifacts and trash , and then the final Dual Audio Output Power Amp of the LA4127.

My closest mark up reference is being at the CA5668 regulator chip and its RED rectangle designation marking and in its RED square foreground seems to show the last half of . . . ?'2 ohms printed on the PCB.

SET UP . . . . .

In a NO POWER /BATTS disconnected test, use metering in its low ohms function.
Then you measure from from IC pin 6 to what looks to be its associative resistor connection . . . .of one of the leads of that ( RED-RED-BLACK band, color code marking) 22 ohms resistor. Then you confirm that the touching of one of its leads results on an almost zero reading / like shorting the meters two test probe leads together. OR . . . . .you could just visually trace the direct foil path to the terminated 22 ohm resistor lead.
Then you go to the OTHER resistor lead and just see if it is being connected to the references small RED square marked up side of the smaller blue cased E-cap.
If so, then you ohmically test across that E-caps two leads to see if it is being dead shorted .
If so . . . . . . .then . . . . .as per the video, lightning actually CAN strike twice on Casio players of this design, using a 6.3 VDC rated E-cap with 5 + volts subjecture on it.
You can then unsolder and lift the defective cap from the board. Or if being a nonsolder-er-er . . . .as of yet!
Just a back and forth /side to side full bending of the cap case should let metal fatigue break loose its two wire leads after 363 full flexures.
Then a retest of the unit . . . .sans the bad E- capacitor . . .with batteries installed should hopefully have the unit making beautiful music for mama-san again.
Then you worry about getting / ordering a like capacitive value of E-cap at on upwards of a 16VDC rating, thereby providing a specs voltage cushion for the future..

If that is not the problem, then we move on to my top center VIOLET square markup as well as the right top sides YELLOW square markup.
BECAUSE like situations with 22 ohm isolative resistors and their following bypass caps also exist at those locations..
And there is being a final u/p reset IC located at the GREEN square markup, its also being associated with that +5V AVDD supply line .

AN INITIAL ASSIST . . . . .

Using another photo, I will now start you on the initial flow path of the pin 6 of the LA5668 and its +5V AVDD supply source.
Pin 6 only has one additional foil connection to its side which likely will be for a bare wire jumper on the other side of the board and it then ends up at the pin 10 area and that foil associated with the end of this jumper, it then only shares its foil with what must be THE 22 ohm resistor, then the other side of that resistor has its foil pad which only has two other adjoining pad connections, one of which must be the pad connection to the + wire of THE suspect E-cap and the other pad, must be associated with carrying on the path of the +5V AVDD supply ever on to its other connection areas of the system.
Now, I can't flop the board over . . . nor meter out . . . to confirm those routings , but I highly suspect that I am being correct.


Le REFERENCE . . . . . .

https://i.ibb.co/FYSTcKX/Casio-CT-638-Audio-Flow-Circuitry-II.png



73's de Edd . . . . . .



.

 

[vbplayer]

I think it might be a good idea to test 6V220μF capacitor out-of-circuit (i.e. desolder, pull off PCB, and test by itself). I may try this too and will let you know my results.

In Post #57, you mentioned "The output of pin 6 of CA5668 is 1.248vdc." Very interesting as I read 2.14V DC here (as I stated in Post #46). Sounds like the same symptom.