rockford 501s one bad channel

[stoke]

this amp came with one not working channel but after replaced all the transistor of the bad channel, pulldown resistor and gate driver transistor i get the audio distorted. the opamp look fine, what other things i have to check?

 

[Perry Babin]

Do you have a scope?

 

[stoke]

i bought one, but i'm waiting for the shipping delivered it hasn't arrived yet.
Perry, what component you replace in most case to fix the distortion on one channel, knowing that all transistor, gate resistor, pulldown resistor and gate drivers transistors are good?

help me on, to see if i can fix this one before the tektronik arrives

 

[Perry Babin]

There's no specific component that causes distortion. Which output transistors failed? I need the exact circuit board designation.

Did any 0.1 ohm source resistors fail?

 

[stoke]

yes found 2 of then with a high value

 

[Perry Babin]

When the source resistors open or read significantly higher than they should, you need to check the low value resistors connected to those source resistors. Specifically which of the source resistors (R...?) failed?

 

[stoke]

Finaly i got my scope!!! all the opamps signals look ok the only dif were on gate drivers for audio amp section
this is the measure the same signal on R141 and Q113 gate

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

maybe later you can tell me how i can fix my scope back light problem, it's a tektronix tds210 i found on ebay with only this problem i hope could be an easy fix.

 

[Perry Babin]

What does the output look like?

I have no information about that scope but if you ask for information on the tekscopes group at Yahoo. Someone there may be able to help. The group is mainly for vintage scopes but some of the members also repair newer scopes.
TekScopes : All about classic Tektronix CRT o'scopes

 

[stoke]

output

Pos

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

neg

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Perry Babin]

Lift D102 and D104. Does that allow the amp to produce audio?

Be careful when doing this. It will defeat the protection circuit and the amp may draw excessive current.

 

[stoke]

ok. i removed both components and turn on the amp,,,, with no problem now what

 

[stoke]

i still having distorted audio on the output

 

[Perry Babin]

Did the output change when you removed the diodes?

 

[Dr Zeus]

I've seen this a couple of times on these rockford amps. Im not really good at troubleshooting audio distortion yet, but you can try searching for broken traces on the component side. Usually somewhere between the RCAs and the crossover card like this.

This amp was a Punch 60dsm which had DC voltage on the affected channel, and then distorted audio on the scope set to AC coupling.

FIX:

 

[stoke]

no, After removed both diodes the output signal did not change or get better.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Sorry for the pics, my scope need the backlight ccfl tube to be replace.

Thanks Dr. Zeus, i know that a bad trace could be the source of the distortion, but i checked the signal from the RCA terminals to each opamps of the affected channel and just found a distortion on the output drivers gate legs with more or less a 14volts distorted signal. But i can Re-check again step by step with the schematic help.

 

[Perry Babin]

Do you have clean audio on both terminals of C111?

 

[stoke]

i found -12.5volts on pin 1,2,3 of u102 i pull out the opamp and the -12volts is still there, i check c197 and im getting -12volts this volt is coming from the rv101... r192 in one side there is -2volts and in the other side there is mvolts

 

[Perry Babin]

Do you have -12v on both sides of C197?

 

[stoke]

Do you have -12v on both sides of C197?

one side, the one connected to pin 3 of u102,

right now i had u102 pulled out , i replace q123, q122, r175, r174 and q113, after that i get -39 volts on pin4 of all opamps now im giong to replace lm337 and lm317