Roll Call: Who's building, built, or thinking of building a beta22?

[MrMajestic2]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif http://i221.photobucket.com/albums/d...6/DSC00092.jpg http://i221.photobucket.com/albums/d...6/DSC00087.jpg http://i221.photobucket.com/albums/d...6/DSC00088.jpg finally arriveD! just a few cruddy quality photos with my unsteady hand on a cell phone camera, proper photos to come once ive cased it up nicely! one question i have, on my first wiring of the b22 i used the same navships wire that fierce freak used in his b22. im however wondering, is there something that is a little more flexible that would be just as suitable to use for the internal wiring? my only "beef" with the navships wire is that it is so resilient to bending it is quite hard to do a "neat" job wiring without wires going all over the place. stranded copper would be perfectly suitable right? what would be a good brand (id hate to end up using something "cheapy" that might bring down my amp!)! thanks guys

Very nice panel. I especially like the headphone logo

 

[el_matt0]

Quote:

Originally Posted by MrMajestic2 /img/forum/go_quote.gif Very nice panel. I especially like the headphone logo

yes, to give credit where credit is due, thanks a ton mrmajestic2 for the brilliant headphone logo you came up with! the second time around looked a lot better than the initial ones u came up with

heh! looks groovy though

 

[gates_2]

um... problem

I was working on a completely unrelated part (stepped attenuator)... things were fine.. all of the sudden, smoke out of the right channel board... the 75 ohm resistor right below Q23

I'm curious as to why this occured at this time, when all was working fine before

i chekced the back... there was a tiny fiber that looked like it was contacting q19, althouh would that be conductive enough to cause the resistor to smoke?

Should I just replace it and try again?(and 100 ohm won't work here, will it?(don't have another 75 ohm)
PIC:


Regards,

Michael

 

[Ferrari]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif um... problem I was working on a completely unrelated part (stepped attenuator)... things were fine.. all of the sudden, smoke out of the right channel board... the 75 ohm resistor right below Q23 I'm curious as to why this occured at this time, when all was working fine before i chekced the back... there was a tiny fiber that looked like it was contacting q19, althouh would that be conductive enough to cause the resistor to smoke? Should I just replace it and try again?(and 100 ohm won't work here, will it?(don't have another 75 ohm) Regards, Michael

That looks really nasty. Have you tried to measure the value of R32? If it's toasted, you should have to replace it with 75Ω.
I also notice that the MOSFET legs look quite smokey (or is that just the smoke from the toasted R32?).

After replacing R32 (if necessary), you might check the voltage on this board against the values as depicted on the PDF file showing the β22 schematic diagram and the operating points available at the β22 website. This can help you to determine if there are more parts toasted or not. (Hopefully not! )

 

[amb]

gates_2, R32 smoking is a sign that Q23 is shorted. Normally there should be negligible current into the gate of R32 (see schematic). Whatever caused it, there be be other damage, so check for shorts between all pins of each output MOSFET (they should all read very high resistance on your DMM), and also R34, R35.

While 100 ohms will "work" as a replacement for R32, 75 ohms is a "tuned" value for best performance.

 

[joneeboi]

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[akione]

Hi All,

First Post , so be gentle

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif um... problem I was working on a completely unrelated part (stepped attenuator)... things were fine.. ... all of the sudden, smoke out of the right channel board... the 75 ohm resistor right below Q23 I'm curious as to why this occured at this time, when all was working fine before Regards, Michael

I had to join up when I saw this. I had exactly the same thing happen to mine.

Working fine and then R32 suddenly burst into flames !
When I stripped the board down and tested the parts I found 1 dead BC550 (not sure which one, unfortunately),
a damaged diode (D9 or 10) and of course R32.

I've not tested the Mosfets yet, but I will.

Colin

 

[gates_2]

indeed...pins 1 and 3 of q23 are shorted

is this a failure of the mosfet itself?

none of the other mosfet pins are showing direct shorts

 

[amb]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif indeed...pins 1 and 3 of q23 are shorted is this a failure of the mosfet itself?

The MOSFET failure is probably a result of another cause, such as overheating due to lack of ventilation or a shorted output, etc.

 

[Tedro]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif um... problem I was working on a completely unrelated part (stepped attenuator)... things were fine.. all of the sudden, smoke out of the right channel board... the 75 ohm resistor right below Q23 I'm curious as to why this occured at this time, when all was working fine before i chekced the back... there was a tiny fiber that looked like it was contacting q19, althouh would that be conductive enough to cause the resistor to smoke? Should I just replace it and try again?(and 100 ohm won't work here, will it?(don't have another 75 ohm) PIC: Regards, Michael

I had the exact same thing happen to me, just out of the blue when I was listening to it. I ended up replacing all the mosfets, D9, and D10, Q17,Q18,Q19 and of course R32 to be functional again.

 

[Tedro]

Quote:

Originally Posted by akione /img/forum/go_quote.gif Hi All, First Post , so be gentle I had to join up when I saw this. I had exactly the same thing happen to mine. Working fine and then R32 suddenly burst into flames ! When I stripped the board down and tested the parts I found 1 dead BC550 (not sure which one, unfortunately), a damaged diode (D9 or 10) and of course R32. I've not tested the Mosfets yet, but I will. Colin

Thanks for Posting, a documented third person with the smoking R32 makes me feel a little better and that im not the only person having problems with their B22. Not that the B22 is a bad amp or anything, Ti is a great guy and I much respect for him. He was able to help me out on several occasions including this minor issue, now I am just trying to figure out that one last issue I have with one of the output resistors on one of my boards

 

[gates_2]

Quote:

Originally Posted by Tedro /img/forum/go_quote.gif I had the exact same thing happen to me, just out of the blue when I was listening to it. I ended up replacing all the mosfets, D9, and D10, Q17,Q18,Q19 and of course R32 to be functional again.

do you think replacing all of the mosfets was necessary? Or jsut the one that failed?

-michael

 

[Tedro]

Quote:

Originally Posted by gates_2 /img/forum/go_quote.gif do you think replacing all of the mosfets was necessary? Or jsut the one that failed? -michael

I think I first replaced the the Mosfets on that side and Q19 and of course the resistor but that did not work. I replaced all of then, again and D9,D10 for the second round. After the second round the Mosfets went thirmal and the output resistors started to smoke

The third time around I replaced Q19,Q17 and Q18 and the board fired right back up. Not sure what exactly happened and or what gave out but I think it was a chain reaction each time I replaced parts.

 

[akione]

Quote:

Originally Posted by Tedro /img/forum/go_quote.gif I think I first replaced the the Mosfets on that side and Q19 and of course the resistor but that did not work. I replaced all of then, again and D9,D10 for the second round. After the second round the Mosfets went thirmal and the output resistors started to smoke The third time around I replaced Q19,Q17 and Q18 and the board fired right back up. Not sure what exactly happened and or what gave out but I think it was a chain reaction each time I replaced parts.

Hmmm, this is interesting. I followed AMB's advice from earlier about testing the mosfets' resistances.
I found that all 4 had very low resistances, so it does look like it took them all out.

It's nice to know I'm not alone

 

[amb]

Replace only those parts that measured bad. If any MOSFET doesn't show up as shorted on the DMM, then keep it there.