#1
I have a Fender 15G Amp that I am having problems with after a little accident. While I was playing a heavy object fell on the input jack of the amp. Ever since, it hasn't worked and gave off a hum.

I thought maybe something was wrong with the input jack so I bought a new one and replaced it. Took the old one out and soldered the new one in but it still has a hum and gets no signal from the guitar. I noticed the fuse was blown and got a new one and installed, still the same hum. I did notice a slight electronic getting hot smell after I put the new fuse in.

Any idea on what would be causing the problem? I do have a multimeter that I was probing on the board with, but I just got it a month ago and I'm relatively new to repairing circuit boards. Any suggestions or advice would be greatly appreciated.
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Last edited by biglou250 at Aug 15, 2011,
#2
If it's under warranty, see about getting it replaced. If not, you might as well buy a new amp. You can probably find a similar or slightly better quality amp for $100 on Kijiji or Craigslist. You'll probably pay that in parts and labour for a repair.
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#3
Yeah, I know these amp are cheap. I got this one for $60 bucks about 5 years ago.

I was hoping though, that it may be an easy fix. Labor will all be done by me if/when I find the problem and the parts are cheap enough.
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Dimebag Darrell
#4
any chance of pictures of top and bottom of the pcb?

EDIT: you may have damaged the traces on the input jack bit of the pcb, and the hum is because you have an open circuit (like having a lead plugged in at the amp and not at the guitar)
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Last edited by GABarrie at Aug 15, 2011,
#5
Quote by GABarrie
any chance of pictures of top and bottom of the pcb?

EDIT: you may have damaged the traces on the input jack bit of the pcb, and the hum is because you have an open circuit (like having a lead plugged in at the amp and not at the guitar)


If pictures would help, I could take it apart again and try get a couple. Any specific areas you need a picture of?

Also possible, I tried to be as careful as possible desoldering the old jack and soldering in the new one. My soldering experience consists of a high school class about 10 years ago so I am a bit rusty. But I don't think the input jack would be giving off a bad electrical odor?
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Dimebag Darrell
#6
it is more likely to be the jack getting pivoted when the object fell on it, lifting the connections at the tip end away from the pcb breaking the traces.

if you can look for any damage to the actual pcb you can try scraping the green coating off and soldering the break shut
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#7
Quote by GABarrie
it is more likely to be the jack getting pivoted when the object fell on it, lifting the connections at the tip end away from the pcb breaking the traces.

if you can look for any damage to the actual pcb you can try scraping the green coating off and soldering the break shut


I'll definitely take a look at that, thanks for the tip!
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Dimebag Darrell
#8
currently debugging a busted 15G myself at the moment :p having a similar issue of buzz and blowing fuses left, right and centre, so got my work cut out for me >.<
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#9
Quote by GABarrie
currently debugging a busted 15G myself at the moment :p having a similar issue of buzz and blowing fuses left, right and centre, so got my work cut out for me >.<


Haha, then good luck to you!
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Dimebag Darrell
#10
I checked the traces on the PCB near the input jack with a continuity test on my multimeter. All 4 prongs on the jack have continuity with a nearby resisitor so I'll assume the traces are still OK.
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#11
So I did a couple more things.

I noticed the red LED wasn't lighting up so I unsoldered it and checked it with AA batteries and it works at 3 volts.

I thought maybe the PCB wasn't getting power and the transformer was what I was smelling. I checked the lead to the PCB from the transformer and get 18volts on the side by side connections and 35 volts on the two connections furthest apart. I left it unhooked to see if it would start smelling but it was working just fine with no smell. So I guess its working just fine.

I visually inspected the capacitors for leaks or bulging but they all look fine. Unfortunately, I don't have a meter to test them. :/

Is it possible a resistor went bad and that would cause a buzz? I haven't got around to checking all of them cause there are about 20 or so total.
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Dimebag Darrell
#12
Could be a resistor, could be a diode. If your multimeter has a setting with a diode symbol next to it (mine is 2kohm) test the rectification diodes (CR7-10). Your problem is sounding identical to mine :p I'm gonna hopefully get some debugging done after work today so will offer up anything I find as an option
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