20 watt LOCO amp, unwanted distortion fault

[rowbi]

Hi guys.

It's my first time posting, and actually my first time troubleshooting a solid state amp (I've built and modded a few small tube amps before).  My experience is that I'm good at soldering, and reading schematics, but not so hot on electronics theory to accurately design my own amps or troubleshoot more complex issues.

I've just bought a LOCO amp (as I used to have one as a kid in the 80's), and it's the 2201 model, there's some brochure pages at the bottom of this link: http://www.locobox.com/ if you want to see it.

The issue is that the power amp seems to be distorted all the time.  I've tried the low and high guitar input and there's always a little bit of distortion in the background.  it also sounds harsh, not a nice smooth OD.  when I plug my guitar into the FX loop return, the distortion is a little worse, so I'm sure it's the power amp part of this combo that's the issue.  when I turned it on after it being delivered, it did smell a little odd.  i at first put it down to just some dust being on the IC heatsink, but I wonder if that could be a faulty component??

does anyone have any ideas about how I can test the caps, (i'm not sure how i can accurately test them) or how to test the IC's or the transformer?  like I said I'm new to this, so I'm not sure if there's something else to check, or how I check the components I think I need to.

lastly, the master volume pot is a little crackly, so I will probably replace, but could that cause this distortion even when it's not being turned?  also the pot crackling is not the same noise as the amp distorting.

I will take photos of the insude of the amp, and record an audio clip of the issue if you would like to hear it.

THanks for any help you can give

Rowbi

[rowbi]

i opened it up, removed the board, and found a wire that the solder joint at both ends was cracked i think this was an earth for one of the pots, but I forgot to confirm this), and another wire with one end that had a cracked joint, and the wire was wiggling in the PCB hole.

after re soldering those, and using some contact cleaner in all the pots and worked them back and forth a lot, everything works fine...

i thought I'd post what I found in case anyone else ever has a similar issue.

when I looked at all the capacitors, none of them showed any signs of overheating or bulging, and no resistors showed any signs of burning out like you sometimes get in tube amps.

Cheers

Rowbi
p.s. if anyone has any LOCO guitar amps for sale, please contact me.  I'm specifically after the guitar models : model numbers 2201, 4102, 4251 or the extension cab 0251.  the model numbers are on the front control panel for the amps, and on the back of all the amps and the cab.
email me at mail@rowbinet.co.uk