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Old 11th September 2011, 11:53 PM   #11
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Q508 and Q502 are also drivers.
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Old 12th September 2011, 02:35 AM   #12
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Ok amp powers up and idles perfectly..

2 of the outputs have 82 volts of rail on them..

Other 2 outputs have no voltage on them..


Any ideas?
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Old 12th September 2011, 02:47 AM   #13
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You need to be more specific. Each of the 4 transistors has 3 legs.

What is the DC voltage on the speaker terminals (one positive and one negative terminal) with the black probe on the amp ground?
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Old 12th September 2011, 02:56 AM   #14
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With Black meter probe on ground ..


Positive speaker terminal:0.14 volts

Negative speaker terminal:0 volts


On the outputs

Q504 and Q507 show 82 volts of rail on the center legs..

On Q505 and Q506 I get 0.04 volts on all 3 legs of each output


Amp has no output
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Old 12th September 2011, 05:04 AM   #15
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If you short pins 1 and 2 of the op-amp indicated in the photo, do you get any square wave oscillation on the outputs?

Be careful, if it's shutting down for some reason, this could cause it to draw excessive current.
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Old 12th September 2011, 05:26 AM   #16
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im gonna test that in a few..

My question is on the regulator U601 (7805) are legs 2 and 3 connected together ??


Because from leg 2 to leg 3 i get 26 ohms is that normal for this amp?
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Old 12th September 2011, 05:51 PM   #17
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I've never had any reason to measure the resistance between those two legs but it seems too low. Pull the regulator and check the board and regulator to see where the low resistance is.
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Old 12th September 2011, 08:07 PM   #18
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im getting the 26 ohms on the pads themselfs from 2-3
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Old 12th September 2011, 09:38 PM   #19
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Do you still read low resistance if you unplug the preamp board?
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Old 13th September 2011, 02:21 AM   #20
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yes
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