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Old 26th August 2009, 02:40 AM   #11
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Are both of the 10 ohm resistors near the RCA jacks within tolerance?

Do you see any distortion on the output when you look at it with your scope?
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Old 27th August 2009, 02:29 AM   #12
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The resistors are good. It looks ok when a tone is injected but with music I cant really tell besides for how it sounds...Rca jacks are good too.. The ppi guy told my that he checked the switches and the Ic on the input side and they seemed ok.. He told me to just start replacing parts but I really just dont want to shot gun parts.. I really want to know exactly what it is..
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Old 27th August 2009, 02:49 AM   #13
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There could be a power supply problem that's causing excessive power supply noise/ripple that only shows up at high power. If that's the case, you'll probably have to drive it hard while monitoring the ±15v, ±rail and ±driver board supplies. You'll have to have the transistors clamped tightly to the sink if you have to drive it hard.

Do you have a way to clamp the transistors to the heatsink and also allow access to the circuit board? If not, you may have to make something like the clamps in the attached image.
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Old 27th August 2009, 10:55 PM   #14
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I already have the amp modified to run with no bottom cover.. What are the test points?
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Old 27th August 2009, 11:28 PM   #15
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Check for excessive ripple/noise on the following points.

* the end pins on the driver boards

* the power supply pins of the op-amps

* the collectors of the output transistors

The noise/ripple on those points should remain relatively constant no matter how hard the amp is driven. You're looking for high frequency noise. Low frequency ripple is likely to be from your DC power supply and probably wouldn't cause the distortion your hearing (unless it's really bad).
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Old 28th August 2009, 01:08 AM   #16
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As the driver cards are "good", I'd suggest checking the drivers to the outputs. I don't have my schematic handy, but usually, they are a TO-92 package close to the output drivers.
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Old 28th August 2009, 01:21 AM   #17
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As the driver cards are "good", I'd suggest checking the drivers to the outputs. I don't have my schematic handy, but usually, they are a TO-92 package close to the output drivers.
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