Rockford 800a2 problem with right channel

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I have trouble with the left channel of my Rockford Fosgate 800a2 amp.
It began with noisy/distorted sounds from the loudspeaker at normal volume.
When I raise the volume up the distortion disapears.
It also stays away when I lower the volume.
When I turned the amp of for about one hour the problem becomes the same again.
First I thought that it was a bad connection to the speakers but now the distortion won't go away anymore, even if I raise the volume up.

I have also checked the gainpots.
Today I send a sine tone to the amp and check the speakerterminals with a oscope:

right channel:
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left channel:
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can anyone tell me whats wrong with this amp???
 
hehe :cool:

this is a good old RFT EO211 made in GDR :D
I think this scope is as old as me.

I checked the op-amps, u102, u104 and the a output (pin1) from u103 looks good.
but the b output (pin 7) from u103 got the problem.
does that mean that u103 is defective or is it something else?

Thank you for your help!!!!!!!!!!!!!!!!!!
 
haa!

I think I have found the problem!

I checked pin 5 and 6 (channel b input and inverted input)
they also got this problem.
So I traced it a little back and found out that c107 is the part where the damaged sine wave comes from!
between r199 and c107 the sine wave looks correct, but between c107 and c108 it looks damaged.

do you think that simply changing this cap will solve the problem or could there be anything else that cause this cap to fail?
 
The cap is cracked and you can see the pin inside of it.
And you can easily pull the pin out.

It also matches with my fault description, because in the summer (when it was warm outside :) the problem disapears when the inputlevel/voltage gets higher.
Or am I wrong?
Should I pay attention to the rated voltage of the cap?
I have found this one: ECQE2683JF
 
Sometimes, the epoxy can be cracked but there's nothing wrong with the cap. If the pin can be pulled out, it's definitely defective.

I don't know if this could be affected by temperature.

The voltage isn't important here. The lowest voltage mylar caps will be rated for 50v. The maximum voltage that can be applied in this circuit is 15v.
 
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