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Old 3rd February 2013, 10:11 PM   #71
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Ok Parts will be here Monday.
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Old 6th February 2013, 04:31 AM   #72
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Installed new 3055/2955

Clamped into sink and powered up.

Amp powers up but is drawing about 5 amps current. The sink is still getting hot around the 3055.

Everything in that circuit is getting hot on the board.

2 1N4003's
1 1.2k resistor

The 3055 is suppose to make +17.5 vdc its only making about 15.5 vdc
The 2955 is suppose to make -17.5 vdc its making about 18.5 vdc

The 2955 does not seem to be getting abnormally warm like the 3055.

Something is drawing the 3055 down and things around it on the board are hot.

Fan is not hooked up. The trim pot for the fan is working. I get a decrease/increase of dc on the white wire when adjusting the pot.

I replaced the D41D8 so I think its good.

Thoughts?
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Old 6th February 2013, 04:37 AM   #73
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Touch all of the op-amps. Are any really hot?
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Old 6th February 2013, 05:01 AM   #74
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I will do that next.

I removed the board and found the trace for the fan ground wire was burned in half.

I dont know if the current condition caused this or this is causing the current condition???

I replaced the trace, both 1N4003's, 1N4746 zener and I am going to re power.

What do you think about the broken fan ground trace before I go further??
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Last edited by seankane; 6th February 2013 at 05:07 AM.
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Old 6th February 2013, 06:01 AM   #75
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Please read #74 first

I replaced the previously mentioned components and repaired the trace.

The amp powers up, idle is stable at about 1.5 amps current draw. Nothing is getting hot, fan works great.

New problem.....grey wire is only producing lower half of waveform.

Fuses are good. Outputs are good.

I touched up some cold solder joints on all the drivers, is it possible that one of the d40/d41 gave out?

The channel wont bias either.

If the d40 or d41 driver was out in the channel, would part of the waveform be missing??
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Old 6th February 2013, 06:06 AM   #76
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Confirm (by touching the legs of the outputs in the distorted channel) that you have positive rail voltage on half of the output transistors.
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Old 6th February 2013, 06:28 AM   #77
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Yes half the outputs in that channel have negative rail and half have positive rail.

The op-amp that feeds that channel from pin 1 has 0.250 vdc on pin 1.

None of the other pins have any voltage except the supply pins.

Both regulators are producing equal voltage now as well.
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Old 6th February 2013, 06:36 AM   #78
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Drive a signal into the channel (no load, about half way to clipping on the bottom). On the output pin of the op-amp for that channel, do you see the top output spiking to near 15v and the bottom barely visible below 0v? If not, post a photo of the output on that pin of the op-amp.
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Old 6th February 2013, 07:05 AM   #79
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The first pic is of the faulty channels op-amp pin 1.

The second pic is what all the rest of the the pins 1&7 on the good channels look like.
Attached Images
File Type: jpg Power 650 op-amp 001.jpg (749.8 KB, 14 views)
File Type: jpg Power 650 op-amp 002.jpg (976.6 KB, 13 views)
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Old 6th February 2013, 07:15 AM   #80
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That means that the op-amp is trying to drive the top half but something in the top half of the circuit isn't allowing the drive to get to the output transistors.

It appears that the other channels are severely underbiased or the channels are being driven to clipping but it's hard to know without the scope settings.
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