Please Help Me Kind Amplifier Enthusiasts

[Toast]

So I just got back into playing guitar, been playing for ~2 weeks now and....my amp just up n stopped working on me.

As far as I know nothing happened to it, nothing hit it, spilled on it, dropped it, nothing.

This is a small practice-type Fender Bullet Reverb (I can go down to the basement and get specifics if you guys need em I'm just lazy :p).

I sat down and tuned my guitar using the cable plugged into a battery powered tuner, so I'm assuming the cable and hardware on the guitar itself are ok and this problem is with my amp.    I turn my power switch on, light comes on and I can hear the faint hiss amps normally makes when it is on, it gets louder if I turn the volume on the amp up (always normal amp noise as far as I know, very faint), and it gets a bit more intense if I turn on the distortion, but playing the guitar (yes I plugged it into the amp :p) produces no sound whatsoever.

I went ahead and opened it up and everything looks ok, like there aren't any obvious poor connections on the inside and no obvious physical damage, but beyond that I don't know what to do here.  Please help.

[R.G.]

If your amp is making the faint hiss and it responds to the volume control, chances are the amp's fine.

Do you know that your guitar cord is good?

Is the volume knob on the guitar turned up to max?

[teemuk]

Should I assume that the cord you use with the tuner was the same you use between guitar and amp? Did you plug straight to amp or through the tuner? You problem is very likely either an intermittant jack or intermittant guitar cord. Question is, is the jack in the amp, in the guitar or in the tuner output - if it has one. Try with different guitar cord first, straight to amp to rule out some of the possibilities.

Edit: One more trouble locating test: Turn reverb to "10". Give the amp a gentle punch. Do you hear a sound?

[Toast]

Ok, the cord is the same and all.  I took the cord out of the tuner and plugged it directly into the amp from the guitar.

I've screwed around with the volume knobs on the guitar (2...Epiphone Special), set em both low, high, one low, one high (the reversed), nothing changes at all.  The volume knobs are a bit loose, I'm not sure why, but its like whatever is keeping them attached to the body is a bit loose...possible problem?

Upon setting reverb to 10 and givin my amp a punch, I get a sound reminiscent of a crappy laser sound effect like you might see in Star Wars or somethin.

I seem to remember getting some sort of audio cue from the amp when I plugged my guitar in, like the hiss would change a bit or something (can't quite recall now though), that does not happen now (could be I'm remembering something that isn't there I guess).

I have an acoustic but it just ain't the same.

Thanks for the assistance though guys, I'll keep checkin back.

[teemuk]

The "audio que" you mention is perfectly normal behaviour and you don't remeber wrong. All guitars pick some noise (like buzz from lamps and computer monitors) to some extend. They are not perfectly "clean" while you are not plugging the strings.

OK then,

1. The "laser" sound you heard originates from the spring reverb tank and indicates that the power amplifier section is working correctly. That is good news but I pretty much expected it because: 2. The hiss originates from the preamp as well and gets amplified too. The gain of the distortion channel is higher, which is the reason for the hiss to get more intense when you switch channels.

However, you did narrow the search area a bit (in case the trouble is something else than what I suspect it might be). We now know that the problem must be at least somewhere before the (spring) reverb recovery stage. That is the stage that amplifies the movement of the reverb springs. If you look at the schematic you will see TL702 opamp marked "U3A". It's top right, right under "Reverb circuit" section. It, and everyhthing after it in the signal path, is at least working correctly.

Follow the signal path towards the input. You will see the other half of the same opamp, U3B. With 99,9% certainty it is allright as well. Rest is unsure but there are some typical fault scenarios:

Now I'm 99,9% sure that your problem is intermittancy: That amp's input jack is a low-quality phone jack soldered straight to PCB. Renew it's solders and your problem is most likely gone. Channel selector switch (S1A & S1B) should be your next suspect but I doubt it's the cause. Judging by the way your amp acts I think that all solder joints of the potentiometers (Again PC board mounted) are allright as well but check them anyway. They will fail sooner or later.

Sorry to say but with all those circuit board-mounted potentiometers, switches and jacks your amp is built like a timebomb when it comes to mechanical problems.

It likely should be a quick and easy job to fix this thing. In worst case you have to buy a new input jack and replace the existing one or something.

I don't know how much you know about electronics and about your soldering skills but judging by the fact that you ask about such simple problem as this I would guess that all this is pretty much new to you. If you are uncertain about your skills you can take the amp to a tech but in this case I would rather take it to that friend of yours who knows a bit about electronics. A tech would charge a lot of money of a very easy job - and it's his right to do so since you pay for his knowhow. However, I don't think that in this case it's worthwhile to pay a lot of money to get a cheap amp (easily) fixed. Your friend will fix the thing in half an hour if you buy him a beer.

Here is a link to the schematic:
http://www.fender.com/support/amp_schematics/pdfs/Bullet_Reverb_Schematic4A7.pdf

[Toast]

Awesome, thanks a million man.  I'm gonna have him check it out.  I'm also gonna try to learn a bit sos I can troubleshoot this sort of thing myself in the future.  I never really thought about how my amp worked but its pretty interesting now that I've been forced to do so.  I know a little about reading electronic schematics and whatnot (my major field of study is Computer Science), but not knowing anything about amps I didn't wanna go screwin around with it as I know what problems that sort of thing can cause for PCs.  

I've done some basic soldering and whatnot in the past, you think this is something I'll likely be ok with?

Again thanks a ton, the info you gave is priceless.  As you said a tech would charge me a lot of money (rightfully) and I'd walk away knowing little to nothing more than I did before my amp broke.

Oh and you said that amps built like this are sort of time bombs....is there anything you would recommend I look for in an amp to ensure longevity?  Given I bought this thing used in '00, I think 7 years is pretty good, but just for the sake of knowin.

[teemuk]

I know a little about reading electronic schematics and whatnot (my major field of study is Computer Science), but not knowing anything about amps I didn't wanna go screwin around with it as I know what problems that sort of thing can cause for PCs.  

I truly respect someone who knows what his skills are and what they are not. Everyone has to start from somewhere and knowing your own limitations is a key to learn and make things right.

I've done some basic soldering and whatnot in the past, you think this is something I'll likely be ok with?

In my opinion resoldering a broken solder joint is easier than making one from the scratch. Note that excessive heat can lift off the PC board traces though. And most modern boards have thin and vulnerable traces that were not designed to cope with heating that repairs cause to them. For example, removing components without damaging the board is pretty difficult and should be avoided if possible. Once you work with printed circuit boards a while you get pretty good idea how they behave in relation to heat.

If you are unsure of your skill levels you can practice - for example with some broken, throw-away equipment. Better be safe than sorry.

Oh and you said that amps built like this are sort of time bombs....is there anything you would recommend I look for in an amp to ensure longevity?  Given I bought this thing used in '00, I think 7 years is pretty good, but just for the sake of knowin.

For longetivity... in my opinion, those board mounted mechanical parts are the weakest link. Each time you touch them they are under tension and just can't handle it for a long time. If the parts are higher quality they usually take abuse in this respect a bit longer than low quality parts. These parts should at least be tightly fixed to the chassis for additional and a lot more sturdier support. Ensuring that is about the only thing what you can do unless you think about completely replacing them, which is usually quite impossible because layouts are tight.

For example, Mesa Boogie comments on the issue like this in article "Point-to-Point Wiring
Myth VS. Reality" (http://www.mesaboogie.com/US/Smith/point-to-point.html):

"Many manufacturers try to put everything on printed circuitry, but we individually mount and point-to-point wire all jacks, switches, transformers and 8-pin power tubes. The reasons are increased reliability and total ease of replacement. If those parts are PC mounted, major disassembly is required to get at them. Even worse, they can cause the whole PC to fracture if they're bashed in hard enough, then the amp is practically non-repairable."

Take a look at Mesa:
http://www.timeelect.com/mbn-1.jpg

Take a look how Marshall does the thing in some amps:
http://www.timeelect.com/mar30-8.jpg

All of these tricks ensure that the mechanical parts are supported by something else besides the PC board. Now it could be argued which way is better. Mesa is easier to repair while Marshall is more compact and thus less prone for wire induced noise, oscillation etc..

7 years is pretty good. My FX pedal with only PCB-attached input-, output- and DC power jacks breaks it's solder joints at least once a year. If the potentiometers and jacks are fixed to chassis as well you might exceed the 7 years - but that solely depends on how good quality the components and assembling have been and how much and how hard you use the equipment. If you buy a new, cheap amplifier it likely won't be a the most reliable piece of equipment anyway.

[Toast]

Awesome, you've really given me a lot to digest.

I see what you're talking about regarding point-to-point.  I was looking at my amp last night and just thinking to myself it looks like I'll have to disassemble the entire chassis to get to that jack.  The estimate from the repair shop is $60 if it is indeed a bad solder on that jack. $60 and who knows how long without my amp is not to my liking,  so I figure I'll give it a shot myself. I'll practice my soldering on some random junk I've got lying around and see what I can do, worst case I utterly screw it up and I've gotta buy a new amp. The amp is only worth ~100 new so I figure its double or nothing here.