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Post subject: Frontman 15G Repair Help
Posted: Tue Feb 05, 2013 4:36 pm
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It seems my amp just stopped working. One day I went to turn it on and no guitar sound came out. When I pump up the gain, I hear a hissing sound. I think someone may have kicked the cord while it was in the input jack, because though I've re-tightened the jack, the cord still wiggles around. I've tested the amp with the auxiliary input and it sounds fine, and the speaker is fine. I opened it up, and I don't smell any burned components. The fuse is fine, and everything seems ship-shape (from what I can see). I'd love to just take out the circuit board and check it out a little closer, but that would require me to de-solder a few components, which I'm not about to do unless I'm sure about what's wrong.

Is the input jack the problem? If it's possible, I would like to know how to test this. I'm a second-year Electrical Engineering student in college, so I'm more than capable of soldering. I've built my own tube amp at home, but I don't know enough about amp theory to just look at the schematic and say "yep, that's my problem." I have access to oscilloscopes, signal generators, a multimeter, the whole nine yards. I just need a little help figuring out how to tell if my input jack is messed up. Any ideas?


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Post subject: Re: Frontman 15G Repair Help
Posted: Tue Feb 05, 2013 5:04 pm
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Try jumpering around the jack with clip leads to the PCB itself.

http://support.fender.com/schematics/gu ... ematic.pdf

Might be hard to find an exact replacement jack. Try these guys:

http://www.darrenriley.com/FenderAmpParts.htm

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Post subject: Re: Frontman 15G Repair Help
Posted: Sun Feb 10, 2013 7:37 pm
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Since you can hear sound (hissing) and you said that someone kicked the cord I would bet that the runs on the PC board are broken. I have repaired a bunch of these. What I do is remove the PC board and flip it over to look at the underside. Look where the jack's prongs go through the board. You will see the thin metal run that is adheared to the board. Right there where the jack prongs are soldered to the board you may see a crack. Maybe a few cracks. What I do is place a piece of wire over the run from the jack prong to the next solder point. Just solder them at these 2 points. A small paperclip will also work. Do as many as are needed to get all the runs repaired. This bypasses the run and will not break again. One hint: when you insert the cord into the amp jack run the cord through the handle on top so that it will not cause damage again should it be yanked on.

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Post subject: Re: Frontman 15G Repair Help
Posted: Sun Feb 10, 2013 7:56 pm
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bob_amos wrote:
One hint: when you insert the cord into the amp jack run the cord through the handle on top so that it will not cause damage again should it be yanked on.


Yes. Then when you yank on or kick the cable you will just jerk the entire amp to the floor where it will smash or bounce. :roll:

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Post subject: Re: Frontman 15G Repair Help
Posted: Sun Feb 10, 2013 8:32 pm
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One would really have to give it a yank to do that. If they are tugging that hard on it there is nothing that will protect it. Most of us are reasonable with the use on our equipment. A small tug directly to the jack will easily snap that run on the PC board. On my amps I run a very long cord so when it is run through the handle it then runs down the back and under the amp. No way that will turn it over. But I would still rather have it tip over on the floor than have the jack ripped out ot the thing. I amways have my amp down on the floor or tipped back on a stand when it will not get yanked off of. My small 15 and 25 series amps do not fit the stand so always sit on the floor. I have 16 Fender amplifiers plus a few other brands and have yet to tip one over.

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Post subject: Re: Frontman 15G Repair Help
Posted: Sun Feb 10, 2013 11:36 pm
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Yes, but considering the cost of some solder, wire, labor, and possibly/likely a new jack, wouldn't it be much better to just throw the amp away and get something better?

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Post subject: Re: Frontman 15G Repair Help
Posted: Sun Feb 10, 2013 11:57 pm
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shimmilou wrote:
Yes, but considering the cost of some solder, wire, labor, and possibly/likely a new jack, wouldn't it be much better to just throw the amp away and get something better?


That's what Fender themselves do with them when one is returned for a warranty claim. They hook-shot the defective amp into the nearest convenient dumpster and give the customer a brand-new unit.

If they can afford to do that because a 10-cent or fifteen-cent part failed in an amp that retails for about eighty bucks and still turn a yearly corporate profit, what do you think that amp is really worth?

:lol:

Arjay

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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 8:36 am
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Normally trashing an amp like this would have been my recommendation, but considering that the OP is a 2nd year EE student in college, I figured it would be worth the time and effort in educational value to help him fix it. 8)

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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 11:18 am
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Thanks for the suggestions, I think I'll try to take out the PC board and do what was suggested when I get a chance. Even if it isn't worth trying to fix, it'll still be a fun time fiddling around.


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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 12:59 pm
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pianokevin wrote:
Thanks for the suggestions, I think I'll try to take out the PC board and do what was suggested when I get a chance. Even if it isn't worth trying to fix, it'll still be a fun time fiddling around.


In my sophomore year (Maybe it was junior. I don't remember as it was 1976! :lol: ), I was working on a Blackface Twin Reverb for a dorm mate in the electronics lab. I was trying to read the B+ voltage with a vacuum tube voltmeter (pre-digital voltmeter :D ). I couldn't get a reading so while holding the probe in one hand, I tapped the power transformer with the other. BIG mistake. The 470 VDC or so knocked me off my stool and threw me backwards 6 feet into the wall behind me. I sat there in a stupor for several minutes. After I regained my senses, I put the amp back in its cab and gave it back to its owner telling him I couldn't figure out what was wrong. :lol: :lol: :lol:

You don't have to worry about high voltages like that, but you still need to be careful when working on any amp. :wink:

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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 4:23 pm
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A guy that I worked for once, used to say; " A good tech should be able to choke down 440." You were just over his limit. :lol:

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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 6:41 pm
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Update: The solder joint and the run that were the problem. The joint was cracked and the run had a break. I'm going into the lab tomorrow to fix them, and all should be good again. Thank you all for the help!


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Post subject: Re: Frontman 15G Repair Help
Posted: Mon Feb 11, 2013 11:03 pm
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Excellent. :D

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Post subject: Re: Frontman 15G Repair Help
Posted: Tue Feb 12, 2013 12:28 pm
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bluesky636 wrote:
After I regained my senses, I put the amp back in its cab and gave it back to its owner telling him I couldn't figure out what was wrong. :lol: :lol: :lol:



Yeah, they should have named the Twin Reverb, "The Intimidator" :lol:

Hell, lesser amps even stand back and give it room!

Art


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