marshall amp has mysterious affliction

  • Thread starter Thread starter Nicole_Rose
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Nicole_Rose

Nicole_Rose

Great White North Girl
i've got a marshall 5150 and the last time i jammed with a drummer it did a weird thing. i had to play it pretty loud to compete with the drummer and bassist and about 45 minutes of that it faded out on me, first losing volume slowly, then more quickly and gone. i thought it was the processor so i unplugged the processor and plugged straight into the amp and had sound again. so i started playing and again, the volume faded, but this time more quickly. i turned down and back up and waited a minute and i had sound again, then as quickly as it came it went. anyway, the amp hasn't done it since, but i haven't played it that loud since either. anyone have a clue what's wrong with it?
 
My marshall did this for a while, its a 100watt super lead. The tech said that it was getting too hot and it was actually melting the solder in some places. It would play fine for a while and then the volume would diminish dramatically. Check that the correct ohmage is selected too?
 
rory said:
My marshall did this for a while, its a 100watt super lead. The tech said that it was getting too hot and it was actually melting the solder in some places. It would play fine for a while and then the volume would diminish dramatically. Check that the correct ohmage is selected too?
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ok that sounds reasonable. i thought the culprit could be the heat somehow. but i don't know anything about amps, i just plug into them. how do i check that the proper ohmage is selected? i looked in my manual, and there's no place designated for that purpose in it. ??
 
gvarko said:
Sounds like there may be some internal protection built in to keep things from melting.
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hey that's cool. i just gotta figure out how to play loud and long without overheating the amp then. but it's a 150w amp, there's a lot of juice running through the thing. :confused:
 
Nicole_Rose said:
hey that's cool. i just gotta figure out how to play loud and long without overheating the amp then. but it's a 150w amp, there's a lot of juice running through the thing. :confused:
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If it turns out that it's just shutting down because of getting too hot and there's nothing wrong with it ..... stick a fan behind it.
I bought a bunch of little "squirrel cage" type fans from WalMart and stick them behind my amps always and keep them cool to the touch.
I like the squirrel cage fans because they take in their air from the sides and don't get blocked by drapes or anything getting sucked up against the fan.
 
Were you plugged into the effect loop of the amp or straight into the amp itself? I had an amp that would do that same thing and it was the cheap jacks in the effect loop-after the effect loop jacks were changed out it was okay...
 
Antone_2006 said:
Were you plugged into the effect loop of the amp or straight into the amp itself? I had an amp that would do that same thing and it was the cheap jacks in the effect loop-after the effect loop jacks were changed out it was okay...
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i was plugged straight into the amp. no effects loop. thanks for the response :)
 
The guys on this BBS might be able to help you out. This is a direct link to the Guitar Amp Trouble Shooting board.
http://music-electronics-forum.com/forumdisplay.php?f=22


I'm no expert, but it sounds like something is going on in the power section, being that it will regain it's composure when you turn the volume down for a second and when you start pushing it again, the problem rears it's head once again.
 
Had that exact same problem on my Marshall JCM900 4100. Intermittent and wouldn't always happen everytime I turned it on. Replaced all my tubes and it fixed the problem.
 
ido1957 said:
Had that exact same problem on my Marshall JCM900 4100. Intermittent and wouldn't always happen everytime I turned it on. Replaced all my tubes and it fixed the problem.
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the 5150 isn't a tube amp though. i wish it was :)
 
I have a Marshall 8040 combo that does the same thing. If I run a patch cable from the FX send into the FX return it works perfectly. You might want to give that a try.
 
is the cabinet impedence wrong??? that'll suck current till it heats badlly...
 
impedence is AC resistence... any friends have a multimeter??? what kinda cab is it??? what does the back of the amp recommend?(probably 8ohms) what does it say on the speaker cab????
 
dementedchord said:
impedence is AC resistence... any friends have a multimeter??? what kinda cab is it??? what does the back of the amp recommend?(probably 8ohms) what does it say on the speaker cab????
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it's not a cab, it's a combo amp. the back reads 4 ohms 150w 8 ohms 100w. but i checked the speakers and they're both 16 ohms.
 
good enough 2 16's paralelled would give you 8ohms as a load.... i'm afraid your gonna have to take it to see the doctor... solid state amps like this rarely have heating/protection tripping problems like what your describing.... i worked with a guy that had a mosfet output marshall that he ran fultilt boogie all the time and it never tripped the circuit ....
 
dementedchord said:
good enough 2 16's paralelled would give you 8ohms as a load.... i'm afraid your gonna have to take it to see the doctor... solid state amps like this rarely have heating/protection tripping problems like what your describing.... i worked with a guy that had a mosfet output marshall that he ran fultilt boogie all the time and it never tripped the circuit ....
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thanks for your assistance dementedchord. i'll take it to the doctor :) the reverb is starting to act up so i had to do it anyway.

thanks again:)
 
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