Help the clueless with a non functional amp!
Moderators: pompeiisneaks, Colossal
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spittingfire
- Posts: 1
- Joined: Sun Mar 08, 2015 8:54 pm
Help the clueless with a non functional amp!
Hello everyone, I just picked up a Carvin X100B off a friend that said it wasn't working. Specifically what that means, I'm not sure; but it has no output. All the tubes in it were blown, and from what I was told the last time it had been plugged in it had produced an electrical fire smile and a miniscule amount of smoke. The fuse is good, but I'm not sure if it was changed after the smoke episode. What should I start looking at to remedy this head. I'll be ordering a new set of tubes, but don't want to install them until I know they wont be immediately blown when I plug it in. I can probably fix whatever is wrong, I'm an A/V Tech/Installer so I can solder and properly meter and all that jazz but I've never dealt with guitar amps before so this is all new to me.
Tear down the wall!
Re: Help the clueless with a non functional amp!
I doubt if all the tubes are blown. But it sounds like you should have someone who is qualified to work on it take a look at it.
Mike
Mike
Re: Help the clueless with a non functional amp!
First off I agree with what has been said already. Find a qualified tech. There are a few things that you can do before doing that but be careful.
Start off by powering it up without tubes in it. If it doesn't blow the fuse then put power tubes in and see if it blows the fuse. After that you will need a meter to test voltages. At least that's how I would start!
Actually......why do you think all the tubes are blown? If they are not lighting up it may have shorted the filament winding.
Start off by powering it up without tubes in it. If it doesn't blow the fuse then put power tubes in and see if it blows the fuse. After that you will need a meter to test voltages. At least that's how I would start!
Actually......why do you think all the tubes are blown? If they are not lighting up it may have shorted the filament winding.
Re: Help the clueless with a non functional amp!
I'm not sure what the point would be of trying to power up an amp which was reportedly previously on fire, unless you're Beavis and you like FIRE! FIRE! FIRE!
Seems to me a good first step would be to remove the chassis and perform a close visual inspection of the circuit board, tube sockets, wiring, and whatever else is inside these things, looking for burnt/scorched/melted items. Take and post some good clear pictures. Figure out exactly what version of the X100B this one is, and try to find a schematic online.
Seems to me a good first step would be to remove the chassis and perform a close visual inspection of the circuit board, tube sockets, wiring, and whatever else is inside these things, looking for burnt/scorched/melted items. Take and post some good clear pictures. Figure out exactly what version of the X100B this one is, and try to find a schematic online.
Re: Help the clueless with a non functional amp!
It says it produced an "electrical fire smell" (spelling corrected) not a fire. I assumed there was already a visual. Highly unlikely it is going to catch fire if it blew a fuse. Powering up without tubes can eliminate certain things if the fuse blows or doesn't right off the bat
drew wrote:I'm not sure what the point would be of trying to power up an amp which was reportedly previously on fire, unless you're Beavis and you like FIRE! FIRE! FIRE!
Seems to me a good first step would be to remove the chassis and perform a close visual inspection of the circuit board, tube sockets, wiring, and whatever else is inside these things, looking for burnt/scorched/melted items. Take and post some good clear pictures. Figure out exactly what version of the X100B this one is, and try to find a schematic online.
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Leo_Gnardo
- Posts: 2585
- Joined: Thu Sep 27, 2012 1:33 pm
- Location: Dogpatch-on-Hudson
Re: Help the clueless with a non functional amp!
Fuse is good, as in it's not blown? What current value is that fuse? Did some "genius" put in an oversize 10A, or 15, 20, 25, 30 amp? I ask because it happens way too often.spittingfire wrote:The fuse is good, but I'm not sure if it was changed after the smoke episode.
Just had a customer drop off his otherwise good-working Fender HR Deville today, popped a fuse a a gig. He zoomed off to Home Despot, and got a spare fuse. It's the right one he thought, it's rated for 125 volts. Then the inevitable meltdown, stinky smoke cloud cleared the club. He didn't know enough to put in a 3 amp fuse, so he just got "the biggest one I could find so it wouldn't blow again."
Just to make it clear (thru the smoke) the fatal fuse change usually happens BEFORE a smoke episode.
Two oversize fuses in one day, that'd be about par for the course.
down technical blind alleys . . .
Re: Help the clueless with a non functional amp!
Read this all before you start. If you don't already know that you can do this safely after reading it, stop and haul the amp to a qualified tech. Part of what we pay techs for is being willing to bet their lives that they can work safely. Sometime just for fun, ask a tech if they've ever been shocked by something they're working on. There is a serious risk of dying if you get into this without the skills to do it safely.
1. Research and build a light bulb limiter. This is a prerequisite. If you can't do the research and find out what one is, and build it successfully, it is my opinion that you would put yourself and others at risk by proceeding with this project.
2. Remove all the tubes. Put in a new, tested fuse of the right value. Connect the amp through the light bulb limiter. Determine from the limiter if there is a large current flowing.
3. If there is, disconnect the primary of the power transformer from the incoming AC power. Try the amp again with the LBL and see if the current is now small. If it is, the PT is involved with the problem, not the AC power wiring.
4. Reconnect the PT primary. Disconnect *ALL* PT secondaries. Try the LBL test again. If it is still high current, the PT is highly suspect and may be dead. If the current is low now, the problem is after the PT.
5. Reconnect the heater secondaries only. Try the LBL again. If the current is still low, the heaters are probably OK, and you should measure and write down the heater voltages for later reference. If the current is high, you'll need to track down the wiring or other problem with the load on the heater windings.
6. If there is zero voltage on the hater windings, use your voltmeter to see if there is line voltage across the PT primary. If there is, and there is zero heater voltage, the PT is dead. This may be from a thermal fuse inside, and there are whole arguments on the net about what to do in this case. My personal opinion is to see if the primary tests open, and if so, replace the PT. Amateur surgery to replace thermal fuses is like hiding your pet rattlesnake in a shoebox in your closed.
7. If the heater voltages are OK, test the voltage on the high voltage winding(s). If they're OK when the transformer windings are open, the problem is further down the power line. If they're zero, use your ohmmeter to see if the windings are open. IF they are open, replace the PT.
8. If the secondary voltages are all OK when not connected, there is a problem with the load. Test the rectifiers and first filter cap for shorted. If they're not shorted, solder a 470K resistor from the + to the - of the first filter cap, disconnect all other loads from the first filter cap, then clip your meter, set to high voltage DC, to the 470K. Again using the LBL, turn on the amp. Do you get high voltage across the 470K? If yes, the problem is in the amp wiring. If not, the problem is in the rectifiers and/or filter caps and associated wiring. Leave the meter connected and turn off the AC and unplug the amp. Watch the meter for when the voltage on the filter cap drops under 40Vdc. Then it is safe.
Those are the first steps. Someone familiar with the process will take about 30 minutes to do that, but they will already have an LBL and will not have to stop at each step and wonder if they are about to die from electrocution.
1. Research and build a light bulb limiter. This is a prerequisite. If you can't do the research and find out what one is, and build it successfully, it is my opinion that you would put yourself and others at risk by proceeding with this project.
2. Remove all the tubes. Put in a new, tested fuse of the right value. Connect the amp through the light bulb limiter. Determine from the limiter if there is a large current flowing.
3. If there is, disconnect the primary of the power transformer from the incoming AC power. Try the amp again with the LBL and see if the current is now small. If it is, the PT is involved with the problem, not the AC power wiring.
4. Reconnect the PT primary. Disconnect *ALL* PT secondaries. Try the LBL test again. If it is still high current, the PT is highly suspect and may be dead. If the current is low now, the problem is after the PT.
5. Reconnect the heater secondaries only. Try the LBL again. If the current is still low, the heaters are probably OK, and you should measure and write down the heater voltages for later reference. If the current is high, you'll need to track down the wiring or other problem with the load on the heater windings.
6. If there is zero voltage on the hater windings, use your voltmeter to see if there is line voltage across the PT primary. If there is, and there is zero heater voltage, the PT is dead. This may be from a thermal fuse inside, and there are whole arguments on the net about what to do in this case. My personal opinion is to see if the primary tests open, and if so, replace the PT. Amateur surgery to replace thermal fuses is like hiding your pet rattlesnake in a shoebox in your closed.
7. If the heater voltages are OK, test the voltage on the high voltage winding(s). If they're OK when the transformer windings are open, the problem is further down the power line. If they're zero, use your ohmmeter to see if the windings are open. IF they are open, replace the PT.
8. If the secondary voltages are all OK when not connected, there is a problem with the load. Test the rectifiers and first filter cap for shorted. If they're not shorted, solder a 470K resistor from the + to the - of the first filter cap, disconnect all other loads from the first filter cap, then clip your meter, set to high voltage DC, to the 470K. Again using the LBL, turn on the amp. Do you get high voltage across the 470K? If yes, the problem is in the amp wiring. If not, the problem is in the rectifiers and/or filter caps and associated wiring. Leave the meter connected and turn off the AC and unplug the amp. Watch the meter for when the voltage on the filter cap drops under 40Vdc. Then it is safe.
Those are the first steps. Someone familiar with the process will take about 30 minutes to do that, but they will already have an LBL and will not have to stop at each step and wonder if they are about to die from electrocution.