Broken Gallien Krueger Fusion 550

Thread Starter

nbtone

Joined Oct 14, 2016
55
Hi,
I just bought a new amplifier and it has a problem. When I turn it on the motorized pots start turning and they go to zero. The led around the power button blinks blue and there is a stuttering hum coming from the speakers. When I switch the mute button the led turns red.
I checked the tubes and found one was bad. I replaced it, and still nothing. I also sprayed the pots and plug-in connectors.
I have basic knowledge of electronic repair, and I have an esr meter, a VOM, and an oscilloscope. Where should I begin in order to diagnose this and repair it?
 

Thread Starter

nbtone

Joined Oct 14, 2016
55
Find a schematic. It makes fault-finding immeasurably easier.
I was hoping someone on this forum might have one. My first instinct tells me that the finals are blown, but I don’t want to delve into it too much without a schematic. I doubt if it’s anything as simple as a case of bad caps. Gallien Krueger is pretty good with quality control from what I know.
 

Jon Hoover

Joined Oct 10, 2019
11
Just a quick question, when you said "new", does that mean new for you or really new? If it is brand new, then I would return it for a working amp or for warranty repair. If it is used, then by all means, tear it open and fix it.
 

Thread Starter

nbtone

Joined Oct 14, 2016
55
ABF56C13-E08A-4581-8B07-032C5D265E72.jpeg
I’ve gotten everything pretty much taken apart. I’ll do some capacitor testing and studying of the schematic, locating different parts of the circuit. Then if that doesn’t solve it I will need some help with testing the different parts of the circuit.
 

Attachments

Thread Starter

nbtone

Joined Oct 14, 2016
55
I’ve gone through and checked all the capacitors with an esr meter, and I changed about a dozen of them. I put the amp back together, and it’s doing the same thing. Anyone have an idea of where to start looking for the problem?
 
Top