CA18 Chines Built Amp. distortion in one channel

[master5string]

hi all i have a CA18 power amplifier that i use for my pa system in my band and at our last gig i had a home made lighting sequencer pluged into one of the speakers that the amp was running and after a few hours all of a sudden the horn on that speaker start having this horrible distotion comming out of it so i check and swaped speaker cables around and traced the problem to the amplifier. at first i though the horn was blown but it seems to work fine on the other channel of the amp. so i have one channel of my amp distorting in the hi range any idears on how to fix this or what the problem could be and how to fix it?. the low range still works fine. i have opend it up and checked all fuses and now im stuck.

[J M Fahey]

Inject a 1V 1KHz audio signal and scope the output.
Check for instability or high frequency oscillations.
With and without load.
Your Zobel Network *might* have blown, leaving the amp unstable.
Good luck.

[Enzo]

Did you swap out the input connections to see if the problem could be on your source material?

[master5string]

Did you swap out the input connections to see if the problem could be on your source material?

yes i did check that also. it seems it is definitly the amp.