Hey everybody,
I recently got this little Fender Frontman 15R project from a nice fellow that had an ad in Craigslist. Free. Sweet! He told me it wouldn't come on and that he had poked around looking for an obvious short, but didn't really have the knowledge nor resources to thoroughly inspect it.
Since I know just about enough about electronics to get me into trouble, and I had just purchased a multi-meter, I brought it home and took the amp apart. Now I have been studying on how to make low-power LM386 style amps for a few months, but have yet to start a project.
Once I got it home I plugged it in and as expected, I got no "On" light and no sound whatsoever.
I got the back off it, I poked around inside and wiggled a few wires, but didn't see anything. I put the back back on and plugged it in, turned it on and the light came on, and normal-sounding hum came from the speaker. Plugged one of my guitars in and got nothing but hum. So, off came the handle and the rest of the hardware necessary to pull the circuit board stuff out. As I was checking the wire connectors on the on/off switch, the ground wire just popped out of the connector. I don't know, but suspect that this amp has been messed with inside since sold new. The bare wire was less than 1/8 in long when crimped. No wire was left in the half-crimped connector. So I replaced the connector with a new one. As I was taking one last look inside and getting it ready to button back together for a test run, I found this:
The chip in the circuit board (Upper right) and the solder on the metal cover.
From the other side:
So, is this silly looking wad of solder on the cover of the jack from the factory, or someone needing to ground the already broken board? I would like to get everyone's suggestions on how to best go about fixing this thing. Scrape to bare copper and try to wire in a conventional jack, or something else? I have very little money to put into this thing, so I might wind up scrapping it and just using the pots and other bits for home-made cigar box amps. The only other amp I have is a Micro-Cube, (Love it!) My soldering skills are fair to good. I really don't want to scrap it since it is in otherwise very good shape. What would YOU do? Would you fix it, and if so, how would you fix it?
Any suggestions would be VERY much appreciated.
Tags:
Looks like the factory soldered the shield to the ground, and also to eliminate people messing with it... Was it already broken off?
I doubt that's your problem, though... just a ground lug. grounding a metal shield reduces environmental noise...
Thanks for that info John. I got the circuit board out of the frame and found more damage. The areas around the contacts are all damaged, or appear to be. I did some research and saw a couple of guys jumper over damage like this. I thought about that for a minute and got to looking over some close-up pictures I took of the circuit board and lo' and behold was more damage by the "drive" button. I am now trying to decide whether to try to fix thing, or try to use the pots, resistors, caps, etc. from it to build other smaller amps. Thoughts? I really don't like to give up on things, but should I, in this case?
Thanks!
it looks like somebody replaced the jack, but used a high wattage gun and burned the pads off the circuit board... totally fixable.
Thanks for the help on that. Kinda what I thought, but my skills on this stuff is minimal. The top picture wasn't clear so I added a couple below. They show another burn. I guess it is repairable as well? Should I check other components with a multi-meter?
Thank you!
Those don't look like burns... they look like goo on the surface??
You can check continuity between the solder joint and the existing trace... you won't hurt anything by scraping back the green mask...
Turns out that was goo, as you suspected. One more question, if you please. Should I resolder the board to the cover, use a jumper to it so it's flexible...?
Thanks for all your help!
Thank you John!
I'll try messing with it tomorrow. I've been concentrating on getting a blog out about how I wind pickups, but I lost two hours work in two "hiccups" with the website's blog software.
Either way you ground the shield should not matter....
where do I find your pickup winding blog?
It doesn't yet exist. It kept disappearing into the ether when I went to post. Spent roughly an hour or so entering the text and pictures and then - poof! - twice. Gotta figure something out. Told Myron I would when he asked.
Got started on the pickup blog today. You can see it in the blogs section. I'll be working on it as I can this week. Hope to be done in a day or three.
Thanks for all the help on the amp! I am on hold on that until I get out to the electronics store on my next supply run, whenever that will be. I need a new soldering tip before I can do anything more.
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