Fender Ultra Chorus, Noisey Left Channel.

[urban warfare]

Hello,
I have a 92' Fender Ultra Chorus that is giving me some issues. The right speaker channel is distorted, and the right speaker has a minimal output. Also the chorus does not work on the left speaker line. I pulled the head and found that if I hook the right speaker line up to the left speaker, I hear the chorus working but the signal is distorted at any level. If I hook the left speaker line to the right speaker, the right speaker plays but at a greatly reduced output compared to the left. I know that there are cold soldered joints because i can hear the tell tale grounding sound when I bang on the top. I also get the grounding sound when run a brush over the inputs, and the the resistor bank below it. Sorry I just found a thread with similar problems.
http://music-electronics-forum.com/showthread.php?t=5525
Any suggestion would be greatly appreciated.
Thanks, have a good one!

[Enzo]

There are two power amps in this amp, one for each speaker. So they are individually driven. In the chorus mode, the dry signal feeds one speaker and the chorused signal feeds the other. It is normal for one speaker not to have chorus sound.

You need to determine if either speaker is bad. It seems your left channel works OK. It is hte side with no chorus, right? Try each speaker connected to the left side electronics. Is one of the speakers weak and distorted? Replace it.

Now it also sounds like the right channel is not amplifying properly. Get the schematic and start troubleshooting. The chorus I bet will sound fine once that amplifier channel is sorted out

[urban warfare]

Update

There are two power amps in this amp, one for each speaker. So they are individually driven. In the chorus mode, the dry signal feeds one speaker and the chorused signal feeds the other. It is normal for one speaker not to have chorus sound.

You need to determine if either speaker is bad. It seems your left channel works OK. It is hte side with no chorus, right? Try each speaker connected to the left side electronics. Is one of the speakers weak and distorted? Replace it.

Now it also sounds like the right channel is not amplifying properly. Get the schematic and start troubleshooting. The chorus I bet will sound fine once that amplifier channel is sorted out

Thanks for the reply Enzo. You definitely correct about one only one signal having the Chorus. The right speaker signal only has the chorus. Your are also correct that my left channel is fine. My right speaker is weak, and needs to be replaced. My right channel is putting out enough power, but the signal is distorted. Last night I re-soldered all the cold joints and cracked joints I could find. This lead me to two IC's ( TLO72's on the schematic,but marked jrc30438 on the chip in the amp.) IC "U1" and "U5" give me a crackling and popping when rubbed with a nylon brush. Particularly pin 3 on both IC's. Does this sound like a faulty IC. I have some TLO72's should I try replacing them? I am waiting on a new multimeter at the moment So i can't jump into full diagnostics yet. My last meter was involved in a high frequency, high high voltage accident. Thanks again for the fast reply, and helpful advice. I really appreciate it. I'm glad I found a place where people will happily share their wisdom.

[Enzo]

PLastic brush most likely making static electricity which comes out as pops. The jrc number is likely a house number, it is very doubtful Fender installed the wrong ICs.

Bet your good meter runnign adn start checking the output ppins of your op amps for unwanted DC offset.