Amp Repair Question

[gordon_39422]

I have a little 15 watt SS Crate amp, I think the model is GFX-15.... It has been sitting around the house unsused, because my son knocked it off a chair, and it hasn't worked since... When it is plugged in, I can turn it on and off and the power light will come on and off, but nothing else happens...

I have taken the amp apart in the past to see if something obvious was out of place on the PCB, but found no evidence of burnt components as a result of a short, or overload... Do any of you electronic gurus have any advice on where to start for troubleshooting? One of my students is in need of an amp, and if I can fix this one, I will give it to him for little or no cost at all....

Thanks for any assistance you may provide,
Allen

EDIT: I guess I should add that I have experience with a soldering iron, and have always been able to repair electronics with good results. In most cases, when components have failed, they are usually easily identifiable by burn marks, or other deformities caused by heat. So anyone who might be reserved to supply info for potential death/injury, please submit your suggestions.

 

[kmcguitars]

Re: Amp Repair Question

I had the same amp with a simular problem. It turned out to be a bad headphone jack. Try it with a set of headphones see if your getting signal?
When you plug headphones in it cuts the signal to the speaker.

 

[gordon_39422]

Re: Amp Repair Question

NO results with the headphone idea! Thanks for the idea, though! Any others?

 

[muttonchopsrule]

Re: Amp Repair Question

kind of obvious, but if you haven't already done so, check the input jack and the speaker connections.

 

[CapoFirstFret]

Re: Amp Repair Question

I was gonna say the same thing...start at the obvious..and work your way further....when something gets dropped and doesn't work, it's usually one of the connections points like a speaker or input jack that gets rattled the most...

 

[gordon_39422]

Re: Amp Repair Question

I just tore it down, and the entire PCB sits on my desk within arms reach... Nothing seems weak or lose.. NOthing outta place... No burnt compnents, no capacitors leaking, or any obvious signs of malfunction... Which parts would quit working after receiving a shock as such, without showing external signs of distress?

 

[STRATDELUXER97]

Re: Amp Repair Question

I just tore it down, and the entire PCB sits on my desk within arms reach... Nothing seems weak or lose.. NOthing outta place... No burnt compnents, no capacitors leaking, or any obvious signs of malfunction... Which parts would quit working after receiving a shock as such, without showing external signs of distress?

Does that amp have a fuse or fuses?

 

[Gearjoneser]

Re: Amp Repair Question

9 times outta 10 it's the solder points that hold the input jack to the PC board.
Even though they look normal, they're often a cold connection if a cord yanks the jack real hard. When the PC board is out of the amp, re-wet the solder connections under the plastic barrel input jack. Do the same on any jack that could short out the amp's sound.

 

[Zhangliqun]

Re: Amp Repair Question

Be EXTREMELY careful tinkering around in any amp. At least in tube amps there are capacitors (filter caps) in there that can hold a fatal charge for days after unplugging it. If you are doing anything inside the amp other than rebiasing it (which applies only to tube amps and requires the amp to be running while you do it), you should unplug it and drain the filter caps FIRST, or working on that amp may be the last thing you ever do.

 

[gordon_39422]

Re: Amp Repair Question

It is a SS amp, no tubes... No fuses to foo with either... It is nearly to the point where i am going to say screw it, but I'll give the solder points a go first....

It wasnt plugged in when it was knocked over, we were packing to go on a trip, and this is that amo I would take, as it is small....

Thanks for the words of cautino on the filter caps... When working on my tube amp, I always drain, unless I am just re-biasing... I have replaced the linear volume pot with taper, and a few other "mods" that were simply a matter of replacing cheap compnents with better ones.....

The PCB is actually 2-part... The main one is about 8 inches long and 2 inches wide... There is a film coming of that one that goes to the DSP PCB which is about 2x4 inches... Nothing really hi-tech...

Thanks guys...

Allen