Hi zaib4tsu,
I wasn't on an ego trip. You were clearly out of your depth on this repair, so I was attempting to get you thinking instead of blindly following instructions. Now I find out you have a good meter. You could have said this a while ago. That is good news, thank you. Why you couldn't just answer my questions is beyond me, we could have been troubleshooting. I'm just sitting back waiting for you to start using your noodle instead of having someone repair it for you.
If you look into my history, you will see that I do help people troubleshoot. But only when they are willing to answer basic questions, like what equipment you have. This is important information that others need to be able to suggest what things you can test. It would have been pointless for anyone to ask you to check semiconductors with a Simpson 260 and not a lot of experience (can blow transistors easily).
Anyway, try and reason this out a little as far as where the excessive current went. Then look at things that would have been damaged if that current had gone that way.
Just because someone tells you something you didn't want to hear doesn't mean that they are wrong or on an ego trip. Look deeper into what people are telling you. Also, read my signature line. That is also valuable information at some points in your life. Anyone's life.
-Chris
This is what you said in your first post:
That is called "shotgunning"
I wasn't on an ego trip. You were clearly out of your depth on this repair, so I was attempting to get you thinking instead of blindly following instructions. Now I find out you have a good meter. You could have said this a while ago. That is good news, thank you. Why you couldn't just answer my questions is beyond me, we could have been troubleshooting. I'm just sitting back waiting for you to start using your noodle instead of having someone repair it for you.
If you look into my history, you will see that I do help people troubleshoot. But only when they are willing to answer basic questions, like what equipment you have. This is important information that others need to be able to suggest what things you can test. It would have been pointless for anyone to ask you to check semiconductors with a Simpson 260 and not a lot of experience (can blow transistors easily).
Anyway, try and reason this out a little as far as where the excessive current went. Then look at things that would have been damaged if that current had gone that way.
Tells us nothing of value, and I have seen units come in that worked for a year with the wrong parts in it that should have blown right away. Just because something works does not mean the sub is a good one. You need to look at the specs for both devices and confirm this. At least list the original part, then the substitute part with the ratings for each and then it can be confirmed, or not, that you aren't fighting a bad substitute. Even that is excellent practice and you learn valuable things that way.
Just because someone tells you something you didn't want to hear doesn't mean that they are wrong or on an ego trip. Look deeper into what people are telling you. Also, read my signature line. That is also valuable information at some points in your life. Anyone's life.
-Chris
You're still on it actually.
You haven't helped at all. You just made huge assumptions without reading my entire post, belittled my knowledge, told me to "give up", and told me I was incapable of repairing my amp. You made it very clear I should go nowhere near it, and hand it to a technician instead. The fact that you still think you've contributed anything useful blows my mind - but as a genuine suggestion - please reconsider the "diy" portion of the site title.
Also "shotgunning" to my knowledge would be a blind replacement of all parts - but I specified clearly in the first post that I first tested and replaced ONLY the damaged ones initially. If you read that then you'd already know I owned a meter.
If you like, you can delete this post along with your useless responses and let the thread run its course.
I would like to apologise to everyone else for having to make this post at all - but to be honest I was genuinely shocked to read the first reply to my thread, from a moderator no less. I am here to learn, and once I do, I would love to share my knowledge with others.
If I gave my amp to a technician, I would learn nothing, and have nothing to contribute in the future. It would also be a far less rewarding experience.
I have now stated multiple times that the subs are not the issue, yet you continue to insult my choices.
Subs were all recommended by a reputable long-term Yamaha technician (avionic on AK) who I trust 100%. In my first post (which you didn't read properly) I actually provided a link to the long thread where all subs were given, if you want to keep looking for trouble where there is none.
Read your own post again.
You'll notice it's because you didn't really ask questions - instead you jumped straight to telling me (in an incredibly condescending manner) that without a long list of expensive tools I should just give up. I own only one item in your list (the DMM).
To appease you, the tools I have are:
- basic soldering iron
- fluke 117 dmm, mega328 component tester
- dbt (home made)
- solder sucker, grounding wrist strap / pad, etc
At this stage perhaps you can respect that I don't want your "help", the honorable thing to do here would be to delete both mine and your useless posts (together) to clean up my thread. I am sure you have a lot to offer in other threads.
Firstly, no one is trying to belittle you, but you also have to accept that for people like Chris and myself who have a made a career out of diagnosing and troubleshooting equipment, that ultimately it has all been hard won knowledge. A lifetime of experience comes into play when faced with something like this.
A good technician will first of all analyse all the evidence in the form of voltage readings and then almost forensically look at that to determine a likely cause of events and where problem areas are likely to be.
Having replaced what you believed to be faulty parts you then went on and replaced pretty much everything silicon related in hope. The possibilities of introducing new problems are very real in doing that. If there had been faulty semiconductors still remaining then there would have been a very good chance of picking those up by careful interpretation of test measurements.
Even so...
The DBT should protect the output transistors in the event of a steady state fault, you should have them in place imo. You could also look to over ride the bias generator and so force a zero bias condition. Replacing the outputs with 470 ohm B-E resistors probably won't work as you hope.
Ultimately you have to accept the limitations in your knowledge, and reading the AK thread only reinforces that view.
Its good that you want to learn, but ultimately this is a complex circuit and just throwing insults around isn't going to do you any favours.
(a lot of the manufacturer printed voltages on the diagram are grossly in error)
Could you explain how to override the bias generator? (i.e. legs of specific component numbers to lift like Hamish suggested). If that is where the problem is, could you perhaps circle on the schematic which parts are responsible for this?
Replacing the outputs with resistors on the other identical amp worked fine - had them in place during repair (relay not closing) and then after replacing a handful of bad-testing semiconductors and resistors the relay closed again. Put the outputs back in afterwards and the amp has been on daily duty for months since. I don't see why I'd need the outputs in place to get matching L/R channel voltages at this stage, but I'm open to correction and can install them if absolutely necessary. I just don't want to take chances with the MT-200s.
PS. I haven't used the schematic voltages for anything, I have been told in the past they are unreliable. You'll notice that it was only Chris who suggested referring to those voltages.
Thanks!
I now have three things to test:
- bias generator deactivation
- dc servo deactivation
- class a deactivation
I'll report back after testing these.
As sesbe suggests. An otherwise good amplifier should work OK in this state, just with no quiescent current in the output stage.
Hi zaib4tsu,
I went back through your thread at AK (also a member there, it's really slow). I've seen the wonderful instrument you use to check components. You didn't list it here either. The other thing you failed to list are the transistors you used as subs with their specs. You have to know what you are doing!
Relying on another person doesn't cut it in technician world. You want to learn, so learn! Don't expect me or anyone else to look up the specs on each part to confirm or deny their suitability. That is your job, no one else's.
What is the #1 reason why good technicians get stuck on a repair? It's #1, should be easy for you to understand.
Technicians get stuck when they mistakenly use a conclusion as a fact.
My point is that you haven't come to any conclusions on your own and have blindly accepted that everything you have been told is correct and that all your work and tests are proper. If that were true, you would be listening to your amplifier now. So instead of insulting me, think about that. Your Yamaha expert on the other site hasn't got your amp working yet, has he? So, what do you think the problem is? I don't think it is his error ... hmmmm. What could the problem be here folks?
My suggestions have been helpful to you. Use your head man, think!
Okay, I don't know what your level of understanding is, but at least I have some sense of what equipment you are relying on. Now, this question isn't an insult or intended to be harmful to your pride in any way. Just answer honestly so that appropriate help can be given to you.
Have you studied electronics at all? If so, what is the highest education in that subject you have attained? This is important for us to know.
Do you have a working understanding of how a diode works and normal voltage drop? Same question for transistors? Do you know the difference between a J-Fet and a BJT transistor?
Do you understand how to calculate the resistance of two resistors in parallel?
These are actually just indicators to help us understand what level of knowledge you have. That's so you can be asked to do something with an expectation that you can return a correct answer, it is not any form of an insult. Maybe I should have another member ask you since you have a problem with me asking you anything.
Just a comment now. It is completely unreasonable to ask for help and direct other people to a thread on a different forum for information, then scold them when they don't. It is up to you to state the information here in your current thread. Please respect the time other people have, you're the one who needs help, not them. You do the work, understand?
Your previous attempt on the AK site didn't work and you are stuck. So, what you need to do is start again fresh. Pretend this is a different amplifier and you are seeing it for the first time. Answer questions fresh and do your work - fresh. If you are determined to continue along the line where you're stuck, guess what? You will always be stuck and this is a waste of everyone's time. You have to start fresh, forget everything you think you know about this set and cover your previous work. I know it's hard to do, but something you are assuming is correct isn't. You have to find out where you went wrong, and doing this over is the only way.
This is your thread and you are asking for help. When you are asked questions, do not reply that they should look at the AK thread with your link. That shows zero respect for everyone else. You're not going to learn a damn thing without putting in some effort on your own.
When you installed the substitute parts, did you check the pinout between the two parts? Did you look up the ratings and compare them (no, you didn't)? Why not start there and check your work from the start. We can help you stay on track, but not if you act the way you are acting.
BTW, DIYAudio means DO IT YOURSELF! Not, have everyone else do it for you.
-Chris
Nope. It is exactly what you did.
I went back through your thread at AK (also a member there, it's really slow). I've seen the wonderful instrument you use to check components. You didn't list it here either. The other thing you failed to list are the transistors you used as subs with their specs. You have to know what you are doing!
Relying on another person doesn't cut it in technician world. You want to learn, so learn! Don't expect me or anyone else to look up the specs on each part to confirm or deny their suitability. That is your job, no one else's.
What is the #1 reason why good technicians get stuck on a repair? It's #1, should be easy for you to understand.
Technicians get stuck when they mistakenly use a conclusion as a fact.
My point is that you haven't come to any conclusions on your own and have blindly accepted that everything you have been told is correct and that all your work and tests are proper. If that were true, you would be listening to your amplifier now. So instead of insulting me, think about that. Your Yamaha expert on the other site hasn't got your amp working yet, has he? So, what do you think the problem is? I don't think it is his error ... hmmmm. What could the problem be here folks?
My suggestions have been helpful to you. Use your head man, think!
Okay, I don't know what your level of understanding is, but at least I have some sense of what equipment you are relying on. Now, this question isn't an insult or intended to be harmful to your pride in any way. Just answer honestly so that appropriate help can be given to you.
Have you studied electronics at all? If so, what is the highest education in that subject you have attained? This is important for us to know.
Do you have a working understanding of how a diode works and normal voltage drop? Same question for transistors? Do you know the difference between a J-Fet and a BJT transistor?
Do you understand how to calculate the resistance of two resistors in parallel?
These are actually just indicators to help us understand what level of knowledge you have. That's so you can be asked to do something with an expectation that you can return a correct answer, it is not any form of an insult. Maybe I should have another member ask you since you have a problem with me asking you anything.
Just a comment now. It is completely unreasonable to ask for help and direct other people to a thread on a different forum for information, then scold them when they don't. It is up to you to state the information here in your current thread. Please respect the time other people have, you're the one who needs help, not them. You do the work, understand?
Your previous attempt on the AK site didn't work and you are stuck. So, what you need to do is start again fresh. Pretend this is a different amplifier and you are seeing it for the first time. Answer questions fresh and do your work - fresh. If you are determined to continue along the line where you're stuck, guess what? You will always be stuck and this is a waste of everyone's time. You have to start fresh, forget everything you think you know about this set and cover your previous work. I know it's hard to do, but something you are assuming is correct isn't. You have to find out where you went wrong, and doing this over is the only way.
This is your thread and you are asking for help. When you are asked questions, do not reply that they should look at the AK thread with your link. That shows zero respect for everyone else. You're not going to learn a damn thing without putting in some effort on your own.
When you installed the substitute parts, did you check the pinout between the two parts? Did you look up the ratings and compare them (no, you didn't)? Why not start there and check your work from the start. We can help you stay on track, but not if you act the way you are acting.
BTW, DIYAudio means DO IT YOURSELF! Not, have everyone else do it for you.
-Chris
I have a suggestion for zaib4tsu.
Just keep replacing parts.
Doesn't matter what parts, or what you use to replace them with.
Just so long as you've replaced everything.
Far easier than ignoring and criticizing those trying to help you.
Personally I'm waiting for your post asking where to buy a can of smoke
Just keep replacing parts.
Doesn't matter what parts, or what you use to replace them with.
Just so long as you've replaced everything.
Far easier than ignoring and criticizing those trying to help you.
Personally I'm waiting for your post asking where to buy a can of smoke
i can understand his frustration i've lost to several A700's until i learned the design relied heavily on matched pairs in the driver stage and the direct coupled stages relied heavily on feedback to remain stable.
the few successes i had where time spent on selecting components after labouriously testing vbe curves in order to find the right devices. not an easy thing even for an experienced tech. a good many of the "Natural Sound" series from Yamaha where like this.
some lemons are not worth trying to squeeze anymore juice out of no matter how many others help operate the press.
the few successes i had where time spent on selecting components after labouriously testing vbe curves in order to find the right devices. not an easy thing even for an experienced tech. a good many of the "Natural Sound" series from Yamaha where like this.
some lemons are not worth trying to squeeze anymore juice out of no matter how many others help operate the press.
That's really useful to know - do you think not using matched pairs could cause the wild voltage swings that are currently there though?
When you say the driver stage do you just mean the drivers (not the pre-driver stage) or drivers/pre-drivers both? Because the driver stage (to my knowledge) is just two transistors, and I could probably swap them for a matched pair from a different NS amp just to try (A1306 / C3298).
Would love to hear some of your stories, interested in learning more about the amp even if I never fix this one.
That is your right and I respect that.
I thought I made it very clear that I am a beginner with only basic tools but now I have a huge post asking about my formal electronics education?
In any case, I will collate a list of all semiconductor substitutes now, perhaps at the very least it'll be useful to someone else in the future even if this thread is dead now.
If anyone is willing to help then feel free to correct my list once posted.
Last edited:
The thread isn't dead, that's entirely up to you. But, the list would be helpful to anyone attempting to help you out. Now, something helpful to you. Try and list the following parameters for both the original and replacement.
VCE, IC, power dissipation, hFE (beta), and fT. You can then confirm yourself, or someone else can help you to make sure your substitutions are suitable. While you are doing this, have a look at the device pinouts, the order of the leads.
Just a quick mention on finding out the characteristics for your semiconductors. Do not use a "replacement guide" of any kind. Technicians call those things "the book of lies", and for excellent reasons. You can look up the exact data sheets in most cases from the manufacturer of the part. For the JIS part numbers you will be looking up, only one company made that part number. There are recent Chinese companies now making the same numbered parts, but only the one Japanese company made the real part. Other companies made similar parts, and they will have different part numbers. I hope that bit of information makes it easier for you. There are some data sheet companies that store scans or the actual sheet, and you can find those answers there too.
Big long posts are an attempt to make things either more clear, or easier for you. You might understand that some day.
-Chris
VCE, IC, power dissipation, hFE (beta), and fT. You can then confirm yourself, or someone else can help you to make sure your substitutions are suitable. While you are doing this, have a look at the device pinouts, the order of the leads.
Okay, fine. Now, how much have you learned so far? Do you understand the basics of how a transistor or diode works? There are reasons why I am asking you these things, and they have zero to do with anyone's ego. Not mine anyway.
Just a quick mention on finding out the characteristics for your semiconductors. Do not use a "replacement guide" of any kind. Technicians call those things "the book of lies", and for excellent reasons. You can look up the exact data sheets in most cases from the manufacturer of the part. For the JIS part numbers you will be looking up, only one company made that part number. There are recent Chinese companies now making the same numbered parts, but only the one Japanese company made the real part. Other companies made similar parts, and they will have different part numbers. I hope that bit of information makes it easier for you. There are some data sheet companies that store scans or the actual sheet, and you can find those answers there too.
Big long posts are an attempt to make things either more clear, or easier for you. You might understand that some day.
-Chris
Yes I understand the basics, regarding your questions about series/parallel resistance / diodes / normal voltage drop. I have a very (very!) basic understanding of the difference between BJTs / JFETs / other transistor types. I can diode test a transistor etc.
I will make a spreadsheet of transistors present and try include the parameters suggested for the original and the replacement.
Which parameters are most important to have as close as possible between original and sub? I imagine that varies depending on the application, but I would really appreciate a basic guide of some description. Feel free to link if one exists, I have searched in the past without much luck.
I will also double check the pinouts of the replacements physically once I'm in front of them again.
I will make a spreadsheet of transistors present and try include the parameters suggested for the original and the replacement.
Which parameters are most important to have as close as possible between original and sub? I imagine that varies depending on the application, but I would really appreciate a basic guide of some description. Feel free to link if one exists, I have searched in the past without much luck.
I will also double check the pinouts of the replacements physically once I'm in front of them again.
if you don't understand why a list of "substitute" semi's is of dubious value (because of parameter spread) then go ahead collate it.
as a newb i suggest you find an old ECG/Philips Semi Conductor List/Replacement Guide and read the section at the beginning covering guidelines as to selecting appropriate replacement semi's (and that's only the tip of the iceburg) that should help you toward understanding why your approach to the problem resulted in failiure.
as a newb i suggest you find an old ECG/Philips Semi Conductor List/Replacement Guide and read the section at the beginning covering guidelines as to selecting appropriate replacement semi's (and that's only the tip of the iceburg) that should help you toward understanding why your approach to the problem resulted in failiure.
Well like I said earlier, the substitutes worked fine in the other identical blown amp (although I changed far less of them obviously), and they have worked for many others in the NS series amps - so I am interested in specifically why you think the subs would be the actual cause of the problem here.
Believe it or not I already went through and checked the parameters of some of the main substitutes (original vs. sub mfg specsheets) and I was fairly mindblown at the differences in some parameters of subs that *many* experienced techs were successfully using. Clearly I don't understand how much variation is appropriate where and when.
I'll read what you suggested anyway. I'd still appreciate any A-700 specific stories if you ever change your mind and decide to share. I am curious if there was a case where the amp wouldn't come out of protection purely because of a poorly matched pair, but you weren't very clear.
If there were specific pairs that were more sensitive (eg. the driver or predriver pairs) I could pull those and replace with a factory pair (even from the other channel) to see if the voltages swings were corrected.
Believe it or not I already went through and checked the parameters of some of the main substitutes (original vs. sub mfg specsheets) and I was fairly mindblown at the differences in some parameters of subs that *many* experienced techs were successfully using. Clearly I don't understand how much variation is appropriate where and when.
I'll read what you suggested anyway. I'd still appreciate any A-700 specific stories if you ever change your mind and decide to share. I am curious if there was a case where the amp wouldn't come out of protection purely because of a poorly matched pair, but you weren't very clear.
If there were specific pairs that were more sensitive (eg. the driver or predriver pairs) I could pull those and replace with a factory pair (even from the other channel) to see if the voltages swings were corrected.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.