Help. My amp is broke! Oh noes!

[mauser]

Great forum. So glad it is here.  Thank you in advance.
I was playing the other night and my Fender amp started acting up.  Loud humming noise and low output of music as it warmed up.
I can't afford a shop right now.  I have been home injured for 19 months, so any help would be most appreciated.
Where do I start?  Willing to follow directions explicitly.
The amp is  a Fender  Chorus.

Again, thanks in advance.

David

[DrGonz78]

Welcome to the place! Well if you and your amp are both broke then this might prove to be a great idea fixing it yourself. Do any of the control knobs on the preamp side of the amp have any effect on this humming sound? Volume knob makes it louder/quieter? EQ controls effect the humming sound in anyway? So this amp has two speaker, correct? Which model of chorus amp is it exactly so we can find the right schematic to post. Look at the speaker, if possible, to see it is being pushed forward in conjunction with the humming symptom. A hum symptom can be DC voltage at the output of the amp and putting vDC on the speaker can ruin the speaker(s). Do you have a multimeter for testing voltages?

[mauser]

I'm in the process of posting a video for the guru's.

[mauser]

To answer some of your questions while loading the video...

Yes 2 12 inch speakers.
Volume makes it louder/quieter.
Ultimate chorus is the model. 
Yes I have a Multimeter.

[mauser]

videos.... turn volume up...

https://www.youtube.com/watch?v=dppKTAfFdAo&feature=youtu.be

https://www.youtube.com/watch?v=4EzkYLA9E5E&feature=youtu.be

[DrGonz78]

Does whacking the top of the amp with your fist give any noticeable difference to how the amp is behaving? What I am thinking here is that perhaps there is a loose connection inside or something on those lines. Bad solder joints on the filter caps might produce hum or other symptoms. Lets us know.

[DrGonz78]

Also check this thread here
http://www.ssguitar.com/index.php?topic=617.msg4256#msg4256

Read and follow Post #2 on that thread about checking the send/return signal paths on the amp too. Send a signal to another amp or send a signal of another amp to the return on your chorus amp. If the return jack inputs a nice loud clear signal then that clears the power amp as the culprit. If the Send effect output is problematic then it is something in the preamp section. If they both sound bad then we will go further from there once we find out.

[mauser]

Gotcha...will do in am after Physical therapy.  (jacked up back and neck)

[J M Fahey]

1) that narrow image is annoying/uncomfortable
2) what happens to noise if all pots are on 0?
3) if hum/buzz dissappears, please post which pot is the one which kills it.

[g1]

  If you can't hit it with your hand, try a rubber mallet or big phone book or even lift one end of the cab and drop it back down on the floor.
The purpose is to see if there is a loose connection inside.

[mauser]

Sorry about the video...all I have is my iPhone for video.

I will go make another video...turning all knobs to zero and then each one on to see if it affects it.
I will also give it  couple whacks....lol.

Brb.

[mauser]

Ok...today...will not play sound at all....but if I waited a few days, it will play for a bit and then do the same thing.  Whacking it did not help.



https://www.youtube.com/watch?v=Md7zTkUfOu4

[DrGonz78]

Bash on it a few more times if you get bored lol. Try wiggling the input jack to make sure it is not something cutting in and out on the signal. The fact that it got worse could be caused by an intermittent connection. Honestly, I would open it up and take some power supply test point voltage checks. Also, at that point I would start checking for bad solder joints. Did you try injecting signal into the return effects jack socket? Also, send the preamp send to another amp to figure out if it is a preamp or power amp issue, or both.

[mauser]

As far as the trying the hooking another amp up to it, to be honest...I don't know how to do that...lol. 

I'm going to order a pencil style solder gun kit with a solder sucker tomorrow.  All I have is a big gun style one.
And get some pot cleaner and a resistor to build a little discharge tool.  Been collecting amp and electronics books.
Might as well learn the theory as I go.  Make it an educational affair.   I'm gonna fix this amp.  It's in perfect shape
....other than being broke...lol

[DrGonz78]

As far as the trying the hooking another amp up to it, to be honest...I don't know how to do that...lol.

Well the mono effects send is essentially the preamp out on your amp, everything before the power amp. The mono effect return is basically a way to input signal into the power amp section and bypass the preamp.

So connect a guitar cable from mono effects send and plug the other end of that cable into the input of another amp. This will test the preamp section of your amp, which at this point it might have the fault. We need to just test it to see/hear what it is exactly going on.

On the other amp look for a line out or another send effects jack. On the other amp we are playing guitar through that amp and sending that signal through effects send(or similar line out) to the effects return of the bad amp. If you want just take an mp3 player and input that signal into the effects return to test the power amp section of the chorus amp. Be careful to keep the volume lowered at first so it is not really loud.

This test will tell us if the preamp is at fault or if it is the power amp.