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Old 22nd September 2011, 09:22 PM   #1
chipper is offline chipper  United States
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Default Distorted LF channel on punch 200a4

I have a punch 200a4 here that has a distorted channel I removed the transistors for that channel and tested them they came out good. But when I put them back in the circuit the channel is still distorted. The other 3 channels work perfectly. I tried to check all the surface mount transistors and resistors all of them measured out good. Any ideas what's going on?
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Old 22nd September 2011, 11:54 PM   #2
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Be sure to check the ones marked 5D and A7.

The 5D is a switching diode with leg 3 being cathode and leg 1 being annode.

The A7 is a dual switching diode with leg 1 as annode and leg 2 as cathode and leg 3 being a common connection.

The annode is where the current flows in and the cathode is where it flows out.

I have found these 2 diodes to be distortion causes many times in Rockford amps.

Also check the A56's and A06's for that channel as well as the 0.1 ohm 2 watt source resistors.

I have had a bad smd resistor cause distortion as well. Take your time start tracing the circuit from the output fets and testing all things in-line.

Does the channel that is distorted have any significant DC present?
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Old 23rd September 2011, 03:23 AM   #3
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Quote:
Originally Posted by seankane View Post
Be sure to check the ones marked 5D and A7.

The 5D is a switching diode with leg 3 being cathode and leg 1 being annode.

The A7 is a dual switching diode with leg 1 as annode and leg 2 as cathode and leg 3 being a common connection.

The annode is where the current flows in and the cathode is where it flows out.

I have found these 2 diodes to be distortion causes many times in Rockford amps.

Also check the A56's and A06's for that channel as well as the 0.1 ohm 2 watt source resistors.



All of the above mentioned I took my time carefully and checked each smd component and those checked out good. But I did find Q103 labled "2A" defective it's a smd PNP transistor shorted one side reads .579 and the other side is shorted. What if I remove this from the circuit?

I have had a bad smd resistor cause distortion as well. Take your time start tracing the circuit from the output fets and testing all things in-line.

Does the channel that is distorted have any significant DC present?
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Old 23rd September 2011, 04:00 AM   #4
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Q103 is shorted by design.

Do you have a scope?
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Old 23rd September 2011, 04:16 AM   #5
chipper is offline chipper  United States
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Quote:
Originally Posted by Perry Babin View Post
Q103 is shorted by design.

Do you have a scope?
Oops! I took it off! And no I don't have a scope. I tried locating possibly a transistor like on the 201S but i couldn't find any.
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Old 23rd September 2011, 04:50 AM   #6
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Lift D101 and D102, one at a time, checking for distortion after lifting each one. Does that eliminate the distortion.
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