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Old 1st April 2008, 01:16 AM   #1
240z4u is offline 240z4u  United States
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Default Repairing blown up D'artagnan 5.1 channel amp

Alright guys, I come to you requesting help. I have a soundstream D'artagnan 5.1 amp. Its the older silver model.

I was running WAY too low of an impedance, not realizing my woofers in my doors were 1ohm. After running it this way for almost a year, I toasted a channel in the amp.

Its very obvious which channel it was, all the bias resistors (that is the name for the big 3w resistors right?) are burnt in half. Those resistors and outputs are toasted.

Now, I removed the output devices and burnt resistors in an effort to get other channels working. No sound output from the other channels. It is not blowing 15 amp fuses like it was before I removed the outputs and resistors.

What else got damaged? I looked online for a service manual with NO luck. I can get photos as well. I do have some experience (little) successfully repairing home audio gear, but this just looks alot different!

Thanks for looking everyone, I would really like to have this unit back working again! I miss it dearly. No, I won't run a super low impedance on it!

Evan

EDIT; I have not actually worked on this amp in over a year. Just dug it out.

One of the coils on the power supply is getting HOT when the amp is on. I also had to replace the two caps in the photo that were destroyed as well. I assume that was from taxing the power supply too much.
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Old 1st April 2008, 01:33 AM   #2
240z4u is offline 240z4u  United States
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Here are a couple pictures.

Thanks Everyone!

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.
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Old 1st April 2008, 01:36 AM   #3
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You can get the schematic diagram for the amp.

Are the 49.9 ohm resistors open on the driver board for the blown channel? If so, the driver transistors may be damaged. The driver transistors should be checked even if the resistors are intact.

The amp should power up if you have pulled the defective output transistors.

Is there any DC on the speaker output terminals of the blown channel (or any other channels)?

Are you getting both positive and negative rail voltage to the other output transistors?

Are you getting positive and negative regulated voltage on the op-amps in the audio section?
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Old 1st April 2008, 01:41 AM   #4
240z4u is offline 240z4u  United States
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Perry thank you for the guidance.

I am going to check everything right now you mentioned. I found the test points for the rail voltage.

I am not sure where to probe for audio op-amp voltage. Ill try to figure it out.

Ill be back, thank you.

Evan
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Old 1st April 2008, 01:50 AM   #5
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http://bcae1.com/temp/tl074.pdf
Look at the various pin configurations to determine the VCC pins. You'll need to check the NE5532, TL072 and TL074 ICs. The 5532s have the same pin configuration as the TL072s.

VCC+ should be approximately positive 15v DC

VCC- should be approximately negative 15v DC
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Old 1st April 2008, 02:35 AM   #6
240z4u is offline 240z4u  United States
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Before I had not fully removed the outputs, just the bias resistors. I pulled bias resistors and the dead outputs. Now the power supply isn't getting abnormally warm. Although two of the large resistors in the power supply are getting much warmer then the rest.

Rail voltage was taken from the test points in the upper left hand part of the board in the first photo I posted above. Rail 50vdc.

.005 vdc on the outputs. Its the same on every channel (except the channel with no outputs). That one has .3v on it.

Evan

BTW, I do have a transistor tester. So I can check the drivers.
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Old 1st April 2008, 02:37 AM   #7
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Are you getting audio from the other channels now?
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Old 1st April 2008, 02:44 AM   #8
240z4u is offline 240z4u  United States
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Perry, I have not tried audio yet. I have it setup in my kitchen. Ill check the chips that you suggested first and see what happens.


PLEASE re read my post above, I actually just edited it for accuracy.

Thanks man - Evan
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Old 1st April 2008, 02:49 AM   #9
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To protect the rest of the transistors, clamp them to the sink before testing for audio. Use a 10 amp fuse in series with the B+ input for further protection.

You only need to check the voltage on the op-amps if you're not getting audio out of the other channels.
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Old 1st April 2008, 02:52 AM   #10
240z4u is offline 240z4u  United States
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I did bolt the amp back together.

Op amps are showing 31vdc across the vcc+ and vcc- terminals. Is this too high?

Thanks - Evan

While I wait to hear back, Ill rig up audio.
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