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Class D Switching Power Amplifiers and Power D/A conversion

41hz and Amp6b Fault
41hz and Amp6b Fault
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Old 18th March 2013, 04:03 PM   #1
Svampan is offline Svampan  Denmark
diyAudio Member
Join Date: Feb 2013
Location: Copenhagen
Default Amp6b, fault in output 1

Hello Diy'ers

I've been trying to make a post on the 41hz forum, but after using 3 different email addresses, I don't get an activation mail. So I'll post my problem here instead:
I've been working the whole weekend to assemble and troubleshoot my first amp 6b. I've been very careful in the assembly, and thought I had some pretty darn good shiny concave solders.

At first the amp would only play on channel 2. I then went through all the solders again, and cleaned the board, only to measure 12v on the cathode of d6 -, and the amp not playing at all. (perhaps the protection of the chip kicks in when rail voltage is coming through a faulty D10?) I've been through various troubleshooting threads, but nothing seems to help. Here's some data that may help in finding the problem:

5.1v over C2
0v over R7
8.2v over c5

2.2v to ground after input caps

12v to gnd on - side of L1, 0.1v on + side
5.9v to gnd on - side of L2, 5.9v on + side

5.8v to gnd on output 2 +, 5.9v for -
0.2v to gnd on output 1 +, 0.1v for -

Measure on cathode to gnd:
5.9v on D8
5.9v on D7
12v on D6
0.2v on D5

I've used this method by Scatchy to check the input paths, and the input resistors seemed ok. over the inductors it read 2 ohm on L2 + & -, and 2 ohm on L1 + and unable to measure on -.

I believe the problem is a fried chip, due to the voltage difference (possibly a short-circuit around pin 26), and possibly a bad solder on L1. The measured rail voltage on output 1 suggest a fried diode, how could this be?

Hope you guys can help me out, anything would be much appreciated!

Here are some pics of the board:

Click the image to open in full size.
Click the image to open in full size.

Last edited by Svampan; 18th March 2013 at 05:08 PM.
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Old 19th March 2013, 10:50 PM   #2
horst303 is offline horst303  Australia
diyAudio Member
Join Date: Nov 2009
Location: Sydney
I can see a big blob on the left inductor, prime candidate.
You may need some flux to convince it to flow under it.
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