Distorted LF channel on punch 200a4

chipper · 22nd September 2011, 08:22 PM

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?

seankane · 22nd September 2011, 10:54 PM

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?

chipper · 23rd September 2011, 02:23 AM

Quote:

Originally Posted by seankane

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?

Perry Babin · 23rd September 2011, 03:00 AM

Q103 is shorted by design.

Do you have a scope?

chipper · 23rd September 2011, 03:16 AM

Quote:

Originally Posted by Perry Babin

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.

Perry Babin · 23rd September 2011, 03:50 AM

Lift D101 and D102, one at a time, checking for distortion after lifting each one. Does that eliminate the distortion.

22nd September 2011, 08:22 PM	#1
chipper diyAudio Member Join Date: Oct 2008 Location: Los Angeles	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? __________________ Feel the PUNCH

22nd September 2011, 10:54 PM	#2
seankane diyAudio Member Join Date: May 2010 Location: Washington State	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? __________________ Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch

23rd September 2011, 03:00 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Q103 is shorted by design. Do you have a scope? __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

23rd September 2011, 03:50 AM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Lift D101 and D102, one at a time, checking for distortion after lifting each one. Does that eliminate the distortion. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

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