Members soundman11 Posted May 19, 2014 Members Share Posted May 19, 2014 OK guys i got a fender frontman amp from a friend and it is not working fight, it has almost no bass at all, the sound is off and scratchy. its not the speaker i checked it with a diffrent amp and it sounds fine.there are no visable signs on the board of bad caps or resisters, not sure what is quit wrong with it but sounds like bad opamp or the out put stage. let me know what u guys think Link to comment Share on other sites More sharing options...
Members onelife Posted May 20, 2014 Members Share Posted May 20, 2014 does the amp have an effects loop or a power amp in? if so, what happens if you plug your guitar into it? Link to comment Share on other sites More sharing options...
Members soundman11 Posted May 20, 2014 Author Members Share Posted May 20, 2014 no it dose not, it has a foot switch, external speaker, and head phone out. normal and drive channel's with 3 band eq, and reverb that works Link to comment Share on other sites More sharing options...
Members WRGKMC Posted May 20, 2014 Members Share Posted May 20, 2014 The only thing you can try is see if headphones sound OK. They likely get their sound from the preamp and before the power amp. If they sound good, then you likely have a blown power amp. If they sound bad its likely something in the preamp, but it depends on where the headphones tap in. If they tap in after the power amp then its like diagnosing it with just the speaker and the issue can be pre or power amp. What will need to be done is to circuit trace the amp. Its done by injecting a test tone into the amp. Then you use a small amp to circuit test the amp. You make a probe with a capacitor in series with the Hot probe so it doesn't short any electrical contacts. A .1uf cap should pass enough AC signal fidelity to hear what's going on. The negative side goes to the amps frame ground. You then start at the jack input then work your way through the circuit stage by stage. If you have a good signal going into a transistor, and a bad signal coming out, you can pretty much guess it was that transistor that's failing. The question from there, is its failing because its lost its proper bias voltage or because the transistor or chip is damaged. There are other signs. Sometimes the component gets hot or shows signs of overheating like discoloration or has a hairline crack.If you do isolate it, then its just a matter of finding the right component to replace it. That's the procedure, but unless you've had some experience testing components, there's nothing you can do but take it to someone who does have the experiences. Its hard to say whether the issue is in the preamp or power amp section. Someone may have pumped too much gain with foot pedals into the front end and blown something up front. Or they may have hooked up extension speakers and knew nothing about matching the load impedance and overheated the output transistors. Checking to see what the guy was doing when he blow it out should provide clues. There's still nothing an amateur can do with it besides take it in and have it repaired. The fix should be under $100 for a small amp like that. Link to comment Share on other sites More sharing options...
Members soundman11 Posted May 20, 2014 Author Members Share Posted May 20, 2014 found the schismatics and the headphones come from the power amp and not from th preamp,so that doesn't help.and btw its all ic's Link to comment Share on other sites More sharing options...
Members WRGKMC Posted May 21, 2014 Members Share Posted May 21, 2014 I thought that would be the case. from your description it sounds like you have a bad output transistor but without troubleshooting it there's no way to be 100% sure. Link to comment Share on other sites More sharing options...
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