No, BD911 and BD912 are active part but both Mouser and Digikey are out of BD911 but RS online still have them. I simply can not understand the advise of the Old Wise one to replace them with other part.
I guess another distributor may hopefully have them, or something equivalent from On Semi might work okay.
It's whatever you feel comfortable with 🙂 and welcome to the real world of fault finding 😉
If you know the outputs are good and the drivers are good and you short the vbe multiplier transistor with a link (to force zero bias) then the output stage is 'safe' and cannot draw excess current. You (imo) have to get it to that initial state to work on it.
The amp will work normally (assuming no other issues) with the multiplier shorted.
Ok, after getting violently ill for a week and a half I am back, and the ammeter has been acquired and setup. Still will be working on testing individual components along the input - output chain.
Should I be considering a brute force approach and replace all of the components of the amplifier circuitry?
Just thinking of possibilities...
Just thinking of possibilities...
That would be the worst thing to do imo. Find the problem by measurement. Fault finding is all about evidence gathering.
If the bulb is still lighting and you can't find anything wrong, then remove the outputs and the drivers and get the amp into a state where it at least powers up without excess current draw. Next work on one channel and build it up. Fit the outputs without drivers and recheck. Next fit the drivers.
If the bulb is still lighting and you can't find anything wrong, then remove the outputs and the drivers and get the amp into a state where it at least powers up without excess current draw. Next work on one channel and build it up. Fit the outputs without drivers and recheck. Next fit the drivers.
I agree with Karl wholeheartedly. It is all about gathering and analyzing the evidence. When you just replace things, you destroy the trail of clues ad that prevents you from ever knowing what the cause was, and of actually solving the fault so it doesn't reoccur.
What you are talking about is called "the shot gun approach". There are specific cases where this is valid, but in your case none of the factors would support that approach.
What you are talking about is called "the shot gun approach". There are specific cases where this is valid, but in your case none of the factors would support that approach.
Holidays and illnesses are finally over and I've been putting this project off.
I'm running into a time/efficiency block where finding parts on the board is extremely time consuming (5-10 minutes/pair of components).
I am hoping there is a way to get a text-searchable service manual (I currently have an unsearchable PDF). If I could just ctrl+f and search for the component number, I could cut each component down to 1-2 minutes.
My first thought was that I need OCR software, but if any of you can link a text-searchable version, that would be excellent.
I'm running into a time/efficiency block where finding parts on the board is extremely time consuming (5-10 minutes/pair of components).
I am hoping there is a way to get a text-searchable service manual (I currently have an unsearchable PDF). If I could just ctrl+f and search for the component number, I could cut each component down to 1-2 minutes.
My first thought was that I need OCR software, but if any of you can link a text-searchable version, that would be excellent.
Hi lucasgg,
Welcome to the frustrating world of audio repair. Some companies did give board diagrams that even indicated an area where a component might be found. That's the exception.
What makes things easier is experience. You recognise what circuit the part is in, where that circuit is on the PCB and narrow your search down that way. Still, sometimes parts are placed in areas that don't make sense. There is no defence or procedure for that and it costs me a lot of extra time. Wasted time.
The only thing you can do is try not to assume anything and just relax and locate parts best you can. Start in the circuit areas they should be in. If you're lucky, the PCB design is mirrored or repeated exactly. If not - a dog's breakfast!
Good luck!
Welcome to the frustrating world of audio repair. Some companies did give board diagrams that even indicated an area where a component might be found. That's the exception.
What makes things easier is experience. You recognise what circuit the part is in, where that circuit is on the PCB and narrow your search down that way. Still, sometimes parts are placed in areas that don't make sense. There is no defence or procedure for that and it costs me a lot of extra time. Wasted time.
The only thing you can do is try not to assume anything and just relax and locate parts best you can. Start in the circuit areas they should be in. If you're lucky, the PCB design is mirrored or repeated exactly. If not - a dog's breakfast!
Good luck!
Therin lies my problem - the board is one big L so a lot of parts are far from a logical location.
Yup, very typical of NAD. I've repaired those before. Some brands are even worse, not that telling you this makes you feel any better.
Relax, use a good, strong light. I try to locate key parts that connect to what I am trying to find. Transistors are good sign posts.
-Chris
Relax, use a good, strong light. I try to locate key parts that connect to what I am trying to find. Transistors are good sign posts.
-Chris
