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millet max diamond buffer debugging

post #1 of 6
12/13/09 at 2:53pm
Thread Starter 
Output transistor burned? I just finished building a Millet Max with diamond buffers, and I believe I've burned one or both of my output transistors in one of my channels. Do I just replace QB8 and QB9? Or are other parts possibly damaged?

LQB8 33mv
LQB9 32mv

RQB9 0V
RQB8 12V

Luckilly I have replacement RB8 and RB9.
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post #2 of 6
12/13/09 at 3:22pm
Quote:
Originally Posted by __redruM View Post
Output transistor burned? I just finished building a Millet Max with diamond buffers, and I believe I've burned one or both of my output transistors in one of my channels. Do I just replace RB8 and RB9? Or are other parts possibly damaged?

LRB8 33mv
LRB9 32mv

RRB9 0V
RRB8 12V

Luckilly I have replacement RB8 and RB9.
Unless you're using MOSFETs, RB8L/R and RB9L/R are supposed to be jumpered out.

Refer to the key differences with BJT diamond buffers here:
http://www.diyforums.org/MAX/MAXbjt.php

So, what did you use for output transistors and do you have a pic or two you can show us?
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post #3 of 6
12/13/09 at 3:48pm
Thread Starter 
Sorry,
Q8 and Q9 I meant Q8 and Q9, I'll edit...
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post #4 of 6
12/13/09 at 3:53pm
Quote:
Originally Posted by __redruM View Post
Sorry,
Q8 and Q9 I meant Q8 and Q9, I'll edit...
In that case, I agree with you. It looks like the left buffer is fine, assuming you're just beginning to setup the DB bias - 33mV is basically OFF for current biasing. Those readings on the right buffer indicate a big problem - possibly a fried output transistor as you said.
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post #5 of 6
12/13/09 at 7:32pm
Thread Starter 
I had a bad soldier joint at RB10. Its dialing in now...
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post #6 of 6
12/13/09 at 7:41pm
Quote:
Originally Posted by __redruM View Post
I had a bad soldier joint at RB10. Its dialing in now...
Glad to hear it was that trivial!
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