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#1
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
This one was not powering up, so I cracked it open.
The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Any advice is appreciated. |
#2
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
In article , Paul wrote:
This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Get the datasheet for the PWM controller. Likely most of the power supply will be copied right off the datasheet, or at least enough for you to figure out what is going on. If the big switching fet isn't shorted, if there is power on the big primary-side capacitor, and you don't see physical damage, and it's not kicking on briefly or crowbarring, then change out the kickstart capacitor (which will be one or two MFD and right near the PWM controller chip). If it doesn't fix the problem, it's still the first step toward diagnosing why the PWM oscillator won't come on. I wrote an introduction to repairing switching supplies without the manual in AudioXPress a couple years ago, and the article is probably worth digging up. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#3
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul wrote:
This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Any advice is appreciated. ** Give the job to someone who knows what they are doing and has the needed safety and test equipment. Yours is definitely a case of " fools rushing in where angels fear to tread". FFS ignore Scott Dorsey, the guy is a dangerous idiot. ...... Phil ..... Phil |
#4
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 2:30 PM, Scott Dorsey wrote:
In article , Paul wrote: This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Get the datasheet for the PWM controller. Likely most of the power supply will be copied right off the datasheet, or at least enough for you to figure out what is going on. If the big switching fet isn't shorted, if there is power on the big primary-side capacitor, and you don't see physical damage, and it's not kicking on briefly or crowbarring, then change out the kickstart capacitor (which will be one or two MFD and right near the PWM controller chip). If it doesn't fix the problem, it's still the first step toward diagnosing why the PWM oscillator won't come on. I wrote an introduction to repairing switching supplies without the manual in AudioXPress a couple years ago, and the article is probably worth digging up. --scott I found your article: https://www.audioxpress.com/article/...power-supplies Thanks much. I will read this and let you know what I find. P |
#5
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 3:32 PM, Phil Allison wrote:
Paul wrote: This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Any advice is appreciated. ** Give the job to someone who knows what they are doing and has the needed safety and test equipment. I have the test equipment....haven't you been paying attention to my posts? Yours is definitely a case of " fools rushing in where angels fear to tread". Yours is definitely a case of "I've got my head up my ass!" FFS ignore Scott Dorsey, the guy is a dangerous idiot. Look in the mirror if you wanna see an idiot! |
#6
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul wrote:
I found your article: ( dangerous article link deliberately snipped ) Thanks much. I will read this and let you know what I find. ** Better make sure your life insurance is paid up and you have updated your will. Wot a ****ing idiot. ...... Phil |
#7
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 4:29 PM, Phil Allison wrote:
Paul wrote: I found your article: ( dangerous article link deliberately snipped ) Thanks much. I will read this and let you know what I find. ** Better make sure your life insurance is paid up and you have updated your will. **** you, numbnuts. I've worked in the electronics field for decades, so I know basic electronics safety. Don't project your own ignorance and stupidity on others. Wot a ****ing idiot. You're a ****wit! Go **** on your Momma's grave! ..... Phil |
#8
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 2:30 PM, Scott Dorsey wrote:
In article , Paul wrote: This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Get the datasheet for the PWM controller. Likely most of the power supply will be copied right off the datasheet, or at least enough for you to figure out what is going on. I found the PWM chip. It's a 1271A, PTAC. So it's this one, if I am not wrong: pdf.datasheetcatalog.com/datasheet/on_semiconductor2/NCP1271-D.PDF I have confirmed that I am getting AC and DC off the first main rectifier, and there appears to be nothing on the secondary of the main transformer. I was NOT able to see a 65kHz driving signal on the driver pin 5, but I assume this is because the oscillator is still off. If the big switching fet isn't shorted, if there is power on the big primary-side capacitor, and you don't see physical damage, and it's not kicking on briefly or crowbarring, then change out the kickstart capacitor (which will be one or two MFD and right near the PWM controller chip). If it doesn't fix the problem, it's still the first step toward diagnosing why the PWM oscillator won't come on. Is the kickstart capacitor either C6 or C7 on page 18? One of the 1.2nF caps? I wrote an introduction to repairing switching supplies without the manual in AudioXPress a couple years ago, and the article is probably worth digging up. --scott |
#9
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul wrote:
On 8/1/2019 3:32 PM, Phil Allison wrote: Paul wrote: This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Any advice is appreciated. ** Give the job to someone who knows what they are doing and has the needed safety and test equipment. I have the test equipment....haven't you been paying attention to my posts? ** I bet you have not got a iso-transformer or any clue of how to use it. Amateurs should NEVER touch a mains switcher supply. Yours is definitely a case of " fools rushing in where angels fear to tread". Yours is definitely a case of "I've got my head up my ass!" ** You just proved beyond any doubt you are a bull****ting nut case and an asshole. Make my day - go ahead, electrocute yourself. |
#10
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul the Lunatic wrote:
------------------------- Phil Allison wrote: Paul wrote: I found your article: ( dangerous article link deliberately snipped ) Thanks much. I will read this and let you know what I find. ** Better make sure your life insurance is paid up and you have updated your will. **** you, numbnuts. I've worked in the electronics field for decades, so I know basic electronics safety. ** You made that bull**** claim before. You know SFA about safety when working on live mains equipment. Wot a ****ing idiot. You're a ****wit! ** FYI to all: This poster is clearly schizophrenic with a death wish. Go **** on your Momma's grave! ** Brainless POS like him would not be missed by anyone. ..... Phil |
#11
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 7:18 PM, Phil Allison wrote:
Paul wrote: On 8/1/2019 3:32 PM, Phil Allison wrote: Paul wrote: This one was not powering up, so I cracked it open. The on-board fuse was still good. There was 120 AC, and about 330 DC on the first rectifier. But there were no DC voltages going to the next board. So it's most likely a power supply issue, but as you know, modern switching power supplies are very complex, and are difficult to troubleshoot, especially without a proper schematic. Any advice is appreciated. ** Give the job to someone who knows what they are doing and has the needed safety and test equipment. I have the test equipment....haven't you been paying attention to my posts? ** I bet you have not got a iso-transformer or any clue of how to use it. Amateurs should NEVER touch a mains switcher supply. Yours is definitely a case of " fools rushing in where angels fear to tread". Yours is definitely a case of "I've got my head up my ass!" ** You just proved beyond any doubt you are a bull****ting nut case and an asshole. Make my day - go ahead, electrocute yourself. Make my day - GO **** DOWN YOUR MOTHER'S THROAT! |
#12
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/1/2019 7:23 PM, Phil Allison wrote:
Paul the Lunatic wrote: ------------------------- Phil Allison wrote: Paul wrote: I found your article: ( dangerous article link deliberately snipped ) Thanks much. I will read this and let you know what I find. ** Better make sure your life insurance is paid up and you have updated your will. **** you, numbnuts. I've worked in the electronics field for decades, so I know basic electronics safety. ** You made that bull**** claim before. You know SFA about safety when working on live mains equipment. Wot a ****ing idiot. You're a ****wit! ** FYI to all: This poster is clearly schizophrenic with a death wish. Go **** on your Momma's grave! ** Brainless POS like him would not be missed by anyone. GO BACK TO BUTT-****ING YOUR DADDY! |
#13
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 2/08/2019 2:44 PM, Paul wrote:
On 8/1/2019 7:23 PM, Phil Allison wrote: Paul the Lunatic wrote: ------------------------- Phil Allison wrote: Paul wrote: Â*Â*Â*Â*Â* I found your article: Â*Â* ( dangerous article link deliberately snipped ) Â*Â*Â* Thanks much.Â* I will read this and let you know what I find. Â*Â* ** Better make sure your life insurance is paid up and you have updated your will. Â*Â*Â*Â*Â* **** you, numbnuts.Â* I've worked in the electronics field for decades, so I know basic electronics safety. Â* ** You made that bull**** claim before. Â* You know SFA about safety when working on live mains equipment. Â*Â* Wot a ****ing idiot. Â*Â*Â*Â*Â* You're a ****wit! ** FYI to all: Â* This poster is clearly schizophrenic with a death wish. Â* Go **** on your Momma's grave! ** Brainless POS like him would not be missed by anyone. Â*Â*Â*Â* GO BACK TO BUTT-****ING YOUR DADDY! Â*Â*Â* Sounds about time everybody remembered to take their meds. geoff |
#14
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 02/08/2019 03:44, Paul wrote:
Abuse snipped Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. He is banned from many usenet and other social media groups for this reason. He is also resident in the kill files of many posters here, and posters responding to him as you have also end up in the kill files, so do not get the hep they would like. With proper precautions, working on SMPS units is perfectly safe. I hate doing it, because I dislike working on SMDs as my eyesight is not what is used to be. -- Tciao for Now! John. |
#15
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
John Williamson is a Prize Moron wrote:
--------------------------------------- Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. ** The one with serious personality issues is YOU - pal. Posting malicious lies about fully identified person is the act of a ****ing psychopath. He is banned from many usenet and other social media groups for this reason. ** OK - go name them, you POS liar !!! Fact is, I have never been banned from any internet forum. He is also resident in the kill files of many posters here, ** Good, those fools don't need to read anything I post. BTW: Only Z grade morons use kill files against serious and intelligent posters. With proper precautions, working on SMPS units is perfectly safe. ** For experienced techs only - not raving maniacs like "Paul". THIS is not the forum for even discussing such matters. It's WAAYYY off topic and fraught with danger for the poster and anyone stupid enough to try advising them. I hate doing it, because I dislike working on SMDs as my eyesight is not what is used to be. ** OK, so you are a brainless, irresponsible, geriatric old ****. FFS hurry up and die. ...... Phil |
#16
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 02/08/2019 09:58, Phil Allison wrote:
Snip abuse and idiocy Sort of proves my point, really. -- Tciao for Now! John. |
#17
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
John Williamson is a Dead **** LIAR wrote:
Phil Allison the ONLY serious poster here wrote: Snip abuse and idiocy ** This stinking **** posted nothing but malicious lies and wild bull****. And he just posted some more. I have no idea exactly what the hell is wrong with the demented old fool but he sure is one KING SIZE ****ing asshole. Sad that folk his age deteriorate into complete ****wits before they die. Be far better if they died first. ..... Phil, very ****ed off by the lunatic scum that post here, unfortunately I already very well know that the world of pro audio is FULL of them. |
#18
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 02/08/2019 12:32, Phil Allison wrote:
.... Phil, very ****ed off by the lunatic scum that post here, unfortunately I already very well know that the world of pro audio is FULL of them. Wonders why he keeps on posting and monitoring the group, if that's his opinion -- Tciao for Now! John. |
#19
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
In article , Paul wrote:
I found the PWM chip. It's a 1271A, PTAC. So it's this one, if I am not wrong: pdf.datasheetcatalog.com/datasheet/on_semiconductor2/NCP1271-D.PDF I have confirmed that I am getting AC and DC off the first main rectifier, and there appears to be nothing on the secondary of the main transformer. I was NOT able to see a 65kHz driving signal on the driver pin 5, but I assume this is because the oscillator is still off. Right. For the oscillator to turn on, you have to have good voltages at HV and Vcc to run the oscillator. The ground has to be good. AND... on a cursory reading of the datasheet: pin 3 (CS) has to have less than 1V on it. If it has more, it will shut down for overcurrent. pin 2 (FB) has to be less than 3V. pin 1 (skip/latch) has to be lower than 8V. If all of these things are true, and the pwm chip is good, it should oscillate. If it's not oscillating, check voltages and if voltages are out of range look for bad electrolytics before you look for bad resistors. And yes, the chips fail. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#20
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/2/2019 10:49 AM, Scott Dorsey wrote:
In article , Paul wrote: I found the PWM chip. It's a 1271A, PTAC. So it's this one, if I am not wrong: pdf.datasheetcatalog.com/datasheet/on_semiconductor2/NCP1271-D.PDF I have confirmed that I am getting AC and DC off the first main rectifier, and there appears to be nothing on the secondary of the main transformer. I was NOT able to see a 65kHz driving signal on the driver pin 5, but I assume this is because the oscillator is still off. Right. For the oscillator to turn on, you have to have good voltages at HV and Vcc to run the oscillator. The ground has to be good. AND... on a cursory reading of the datasheet: pin 3 (CS) has to have less than 1V on it. If it has more, it will shut down for overcurrent. pin 2 (FB) has to be less than 3V. pin 1 (skip/latch) has to be lower than 8V. Pins 1 and 3 had 0 Volts. Pin 2 had 1.3 Volts. Pin 6 has about 2 Volts. Pin 8 has about 320 Volts on it, coming off the first rectifier. Is that normal? If all of these things are true, and the pwm chip is good, it should oscillate. If it's not oscillating, check voltages and if voltages are out of range look for bad electrolytics before you look for bad resistors. And yes, the chips fail. --scott |
#21
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
John Williamson wrote:
John Williamson is a Dead **** LIAR wrote: Phil Allison the ONLY serious poster here wrote: ** This stinking **** posted nothing but malicious lies and wild bull****. And he just posted some more. I have no idea exactly what the hell is wrong with the demented old fool but he sure is one KING SIZE ****ing asshole. Sad that folk his age deteriorate into complete ****wits before they die. Be far better if they died first. ..... Phil, very ****ed off by the lunatic scum that post here, unfortunately I already very well know that the world of pro audio is FULL of them. |
#22
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
John Williamson wrote:
Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. He is banned from many usenet and other social media groups for this reason. This is true. Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem. But.... everybody has to start somewhere and if you don't try you'll never learn. He is also resident in the kill files of many posters here, and posters responding to him as you have also end up in the kill files, so do not get the hep they would like. He posts interesting and accurate stuff often enough that I am reluctant to killfile him, although he will go on these weird rants occasionally. With proper precautions, working on SMPS units is perfectly safe. I hate doing it, because I dislike working on SMDs as my eyesight is not what is used to be. Two things changed my mind about this: the Optivisor magnifier (accept no cheap Asian substitutes!) and the hot tweezers. The tweezers allow you to pick up an smt resistor, put it aside, then put it back as needed. It makes working on smt discretes much much easier. I had no idea how wonderful either one of these things was until I tried them. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#23
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Scott Dorsey wrote:
He is banned from many usenet and other social media groups for this reason. This is true. ** I challenge you to say which forums you think they are. Cos I know I have never been excluded from any internet forum. However, I am responsible for the demise of AAPLS, a intolerable nest of crooks & vipers so I am justly proud of doing that. ...... Phil |
#24
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/2/2019 5:46 PM, Scott Dorsey wrote:
John Williamson wrote: Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. He is banned from many usenet and other social media groups for this reason. This is true. Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem. But.... everybody has to start somewhere and if you don't try you'll never learn. I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. What more do you need? And having been a microwave/Radio frequency engineer for nearly 3 decades, I'm not likely to electrocute myself on the bench! But I'll admit I don't trouble-shoot modern switching power supplies very often. But it can't be denied that these are NOT trivial circuits to diagnose, especially WITHOUT a proper schematic! And even your article mentions the when-in-doubt-replace-it, brute force approach to repairing these tough-dog problems. I've certainly successfully done this in the past, but I'm not sure I wanna do that on this unit, because my stock of spare parts is not what it used to be. :/ This unit might end up on Ebay..... Haha! He is also resident in the kill files of many posters here, and posters responding to him as you have also end up in the kill files, so do not get the hep they would like. He posts interesting and accurate stuff often enough that I am reluctant to killfile him, although he will go on these weird rants occasionally. With proper precautions, working on SMPS units is perfectly safe. I hate doing it, because I dislike working on SMDs as my eyesight is not what is used to be. Two things changed my mind about this: the Optivisor magnifier (accept no cheap Asian substitutes!) and the hot tweezers. The tweezers allow you to pick up an smt resistor, put it aside, then put it back as needed. It makes working on smt discretes much much easier. I had no idea how wonderful either one of these things was until I tried them. --scott |
#25
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
In article , Paul wrote:
On 8/2/2019 5:46 PM, Scott Dorsey wrote: Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem. But.... everybody has to start somewhere and if you don't try you'll never learn. I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. Get a load bank and a storage scope and you'll probably be set. The storage scope is REALLY handy to look at the startup of the pwm ic because it's only a few milliseconds long. If it's not repeatedly shutting down, it can be sometimes shutting down on the first try, and then the storage tube tells you what is going on. BUT... the good news is that with these all-in-one PWM ICs, there are only a few static voltages that can cause it to turn on or off, so usually by looking at static voltages you can see what is going on. With discrete transistor PWM circuits you need the storage tube. If you haven't used the ESR meter on every electrolytic, now is the time. Even if they aren't related to the problem, you may pre-empt future failures. And having been a microwave/Radio frequency engineer for nearly 3 decades, I'm not likely to electrocute myself on the bench! This puts you in the category of the "goddamn white hat engineers" and makes it that much less likely that you should touch a soldering iron. I'm in that category myself, but at least I don't have a PhD so I am reasonably safe. But I'll admit I don't trouble-shoot modern switching power supplies very often. But it can't be denied that these are NOT trivial circuits to diagnose, especially WITHOUT a proper schematic! I apprenticed at a TV repair shop in the days of sweep tubes locked up in high voltage cages and all the set voltages being derived from the flyback, and it was amazing seeing some of the tricks. Guys used to run a TV set in series with a 500W light bulb as a current limiter so they could keep them going long enough to diagnose oscillation issues. Sometimes with schematics, but mostly without. And even your article mentions the when-in-doubt-replace-it, brute force approach to repairing these tough-dog problems. I've certainly successfully done this in the past, but I'm not sure I wanna do that on this unit, because my stock of spare parts is not what it used to be. That's easy to fix with a digikey order. Pick up ten of every common PWM chip too, because sooner or later you'll need them. This unit might end up on Ebay..... Haha! See, that is giving up. That is not right. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#26
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul :
On 8/2/2019 5:46 PM, Scott Dorsey wrote: John Williamson wrote: Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. He is banned from many usenet and other social media groups for this reason. This is true. Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem. But.... everybody has to start somewhere and if you don't try you'll never learn. I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. What more do you need? Other than what Scott suggested, an isolation transformer would be a good safety measure. The input circuit typically carries all of the (hazardous) potential of the wall socket. Phil also said this but the screed had begun. -snip remaining- david --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
#27
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 8/3/2019 8:46 AM, Scott Dorsey wrote:
In article , Paul wrote: On 8/2/2019 5:46 PM, Scott Dorsey wrote: Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem. But.... everybody has to start somewhere and if you don't try you'll never learn. I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. Get a load bank and a storage scope and you'll probably be set. The storage scope is REALLY handy to look at the startup of the pwm ic because it's only a few milliseconds long. If it's not repeatedly shutting down, it can be sometimes shutting down on the first try, and then the storage tube tells you what is going on. BUT... the good news is that with these all-in-one PWM ICs, there are only a few static voltages that can cause it to turn on or off, so usually by looking at static voltages you can see what is going on. With discrete transistor PWM circuits you need the storage tube. Good point. A storage scope would be a nice addition. If you haven't used the ESR meter on every electrolytic, now is the time. Even if they aren't related to the problem, you may pre-empt future failures. And having been a microwave/Radio frequency engineer for nearly 3 decades, I'm not likely to electrocute myself on the bench! This puts you in the category of the "goddamn white hat engineers" and makes it that much less likely that you should touch a soldering iron. I'm in that category myself, but at least I don't have a PhD so I am reasonably safe. I've done plenty of bench engineering, and REAL engineers do at least SOME of their own soldering! But I'll admit I don't trouble-shoot modern switching power supplies very often. But it can't be denied that these are NOT trivial circuits to diagnose, especially WITHOUT a proper schematic! I apprenticed at a TV repair shop in the days of sweep tubes locked up in high voltage cages and all the set voltages being derived from the flyback, and it was amazing seeing some of the tricks. Guys used to run a TV set in series with a 500W light bulb as a current limiter so they could keep them going long enough to diagnose oscillation issues. Sometimes with schematics, but mostly without. And even your article mentions the when-in-doubt-replace-it, brute force approach to repairing these tough-dog problems. I've certainly successfully done this in the past, but I'm not sure I wanna do that on this unit, because my stock of spare parts is not what it used to be. That's easy to fix with a digikey order. Pick up ten of every common PWM chip too, because sooner or later you'll need them. This unit might end up on Ebay..... Haha! See, that is giving up. That is not right. The "shotgun" approach of replacing components, until the unit works, often does work, but I have to balance the cost of the parts, and what I want to spend my time doing, versus what I expect to gain at the end. But you are right: I'm kinda lazy, and I'm more into the money, than the knowledge, to be honest, especially at my middle age. I prefer to call it: Selective Cut and Run! I mean, sometimes you can make more money, and save yourself some aggravation, by selling the parts of a unit, instead of repairing it yourself. --scott |
#28
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
Paul the Raving Lunatic and Psychopath wrote:
-------------------------------------------- I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. What more do you need? ** A functioning brain and is also needed. And an earth leakage circuit breaker. And having been a microwave/Radio frequency engineer for nearly 3 decades, I'm not likely to electrocute myself on the bench! ** What an absurd non-sequitur. Paul has been a schizophrenic most his life too. But I'll admit I don't trouble-shoot modern switching power supplies very often. But it can't be denied that these are NOT trivial circuits to diagnose, especially WITHOUT a proper schematic! ** Paul simply has no ****ing idea why he is being criticized by me or anyone else. Like I posted already, no-one will miss him when he dies. ..... Phil |
#29
Posted to rec.audio.pro
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Anyone have a Schematic for a Fender Acoustasonic 90?
On 3/08/2019 9:52 PM, Paul wrote:
On 8/2/2019 5:46 PM, Scott Dorsey wrote: John WilliamsonÂ* wrote: Please check Phil Allison's previous posting record. He has a habit of accusing others of suffering from his own shortcomings. While he has a reasonable knowledge of certain aspects of the audio business, he shows, when posting, personality problems which vary in seriousness for no apparent reason. He is banned from many usenet and other social media groups for this reason. This is true. Now, he does have a good point that the original poster likely doesn't have the right equipment or skills to diagnose the problem.Â* But.... everybody has to start somewhere and if you don't try you'll never learn. Â*Â*Â* I've got a Tektronix 465M o'scope, a digital multimeter, and an ESR meter. Â*Â*Â* What more do you need? Maggy-lamp for a quick check on things before diving in. Check switching transistors and PWM controller chip for cracks in casing. Also some have a opto-isolator than can blows up. geoff |
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