Blown Fuse Problems

[JacksonSMITH]

Hi guys, I have a JCM 2000 dual super lead amp with a 1960A cabinet. I have been experiencing the same dilemma since April of this year and my local repair guy hasn't been able to correct the problem. Something internal is blowing my fuse, a short possibly? I'll turn on my head and let it warm up for 3-5 minutes, turn on the stand-by, play on either clean or the crunch channel (the fuse has blown while playing on either channel) and sure enough the fuse on the left side of the amp continues to blow. I brought it into Long & Mcquade, they switched out the fuse, we warmed the amp up, same process, everything's fine. It wasn't played for long, 2 minutes. They switched between the clean and crunch channels everything seemed fine. I brought it home, hooked it up, and sure enough, not 5 minutes into playing through the amp, the fuse blows.

I have had the amp plugged through the extension cord in one of the pictures . We just moved into a new house, but, I did have the same failure in the old house that we moved out of. Which at the time I was plugging the amp through a Furman Power Conditioner, which I still own.

I am studying Electronics and Instrumentation. I'm just beginning to get my feet wet within the field and I was hoping I can get some insight as to how to approach troubleshooting this problem on my own. The problem has occurred 4 times now.

 

[johan.b]

Sound like a bad power tube to me. Did anyone replace the tubes when the fuse blew or did they just put a new fuse in?
J

 

[JacksonSMITH]

Hi J, yes they did replace the power tubes. I attached the receipt from the initial repair back in April.

 

[Guitar-Rocker]

Hi guys, I have a JCM 2000 dual super lead amp with a 1960A cabinet. I have been experiencing the same dilemma since April of this year and my local repair guy hasn't been able to correct the problem. Something internal is blowing my fuse, a short possibly? I'll turn on my head and let it warm up for 3-5 minutes, turn on the stand-by, play on either clean or the crunch channel (the fuse has blown while playing on either channel) and sure enough the fuse on the left side of the amp continues to blow. I brought it into Long & Mcquade, they switched out the fuse, we warmed the amp up, same process, everything's fine. It wasn't played for long, 2 minutes. They switched between the clean and crunch channels everything seemed fine. I brought it home, hooked it up, and sure enough, not 5 minutes into playing through the amp, the fuse blows.

I have had the amp plugged through the extension cord in one of the pictures . We just moved into a new house, but, I did have the same failure in the old house that we moved out of. Which at the time I was plugging the amp through a Furman Power Conditioner, which I still own.

I am studying Electronics and Instrumentation. I'm just beginning to get my feet wet within the field and I was hoping I can get some insight as to how to approach troubleshooting this problem on my own. The problem has occurred 4 times now.

By chance have you tried the amp at home through a different speaker cabinet? You may have an issue with the cab connection plate jack, a speaker, or your speaker cable.

 

[ampmadscientist]

Hi guys, I have a JCM 2000 dual super lead amp with a 1960A cabinet. I have been experiencing the same dilemma since April of this year and my local repair guy hasn't been able to correct the problem. Something internal is blowing my fuse, a short possibly? I'll turn on my head and let it warm up for 3-5 minutes, turn on the stand-by, play on either clean or the crunch channel (the fuse has blown while playing on either channel) and sure enough the fuse on the left side of the amp continues to blow. I brought it into Long & Mcquade, they switched out the fuse, we warmed the amp up, same process, everything's fine. It wasn't played for long, 2 minutes. They switched between the clean and crunch channels everything seemed fine. I brought it home, hooked it up, and sure enough, not 5 minutes into playing through the amp, the fuse blows.

I have had the amp plugged through the extension cord in one of the pictures . We just moved into a new house, but, I did have the same failure in the old house that we moved out of. Which at the time I was plugging the amp through a Furman Power Conditioner, which I still own.

I am studying Electronics and Instrumentation. I'm just beginning to get my feet wet within the field and I was hoping I can get some insight as to how to approach troubleshooting this problem on my own. The problem has occurred 4 times now.

You have to run the amp for 30 minutes at least before you check the bias stability.
Have amp guy read this:
http://www.drtube.com/en/modifications/jcm2000-stable-bias-mod

Check the numbers on the power amp board and test the bias stability.

Replacing the tube might not really fix the problems.

 

[Ken]

Would anyone think $240 is a lot for the work done, and he didn't even fix the problem?

Ken

 

[mickeydg5]

That is a limited edition 2005 model. It should have the upgrade newer board.


Tell Long & Mcquade to finish the job after checking and testing everything appropriate.


Is that a genuine speaker cable from amplifier to cabinet?
Did you check total impedance of the cabinet through the cable with a multimeter?

 

[JacksonSMITH]

Hey, thanks for the speedy replies.

Mickeydg5, I measured the impedance from my speaker cable while plugged into the left jack on the cab and it was measuring 3.8 ohms. I took off the back piece and took a few pictures. Not sure if I connected the black's and red's improperly or if the polarity matters.

It is a genuine speaker cable, it's a Yorkville sound 18/2 GA speaker cable. It's a fairly new cable, I'm pretty sure I bought it earlier this year.

Should I test the impedance of each individual speaker?

I've had my selector switch (4ohms/8ohms) set to 8 ohms with my speaker cable running from the left jack on the cabinet to the right speaker outlet on the amp. Which has always been my norm for setting the speaker cable up with the amp and I've never had this consistent problem before.

The fuse that blew was rated for 250V 1A.

 

[JacksonSMITH]

By chance have you tried the amp at home through a different speaker cabinet? You may have an issue with the cab connection plate jack, a speaker, or your speaker cable.

I unfortunately don't have another speaker cabinet to test the amp through. The speaker cable is new, bought this year I believe. I tested the impedance of the cable through the cab and it was measuring 3.8 ohms.

Sound was originally coming out of the cab, when it was working, crystal clear but then something triggered the fuse to blow.

 

[ampmadscientist]

Would anyone think $240 is a lot for the work done, and he didn't even fix the problem?

Ken

First, I would have charged nothing to fix nothing.
Second I would have taken more than 10 minutes. Experience counts for something.

I don't fix it, they don't pay.

I suspect circuit board is bad.

 

[JacksonSMITH]

Thanks for the replies guys. Long live Mr. Lemmy Kilmister! I'll have to take it back and see what they can do. I suspect it has something to do with the circuit board as well.

 

[Steeveejay]

Thanks for the replies guys. Long live Mr. Lemmy Kilmister! I'll have to take it back and see what they can do. I suspect it has something to do with the circuit board as well.

Hey Jackson , I had a similar experience in a house i just moved into.
this land lord seemed to do his own electrical wiring . needless to say he got it wrong . any how , any thing i plugged in at one end of the house either tripped a breaker or fuse after a short ,,, time . I found the problem with a Wall outlet phase checker . It also lets you know if there's a ground problem, looks something similar to this gadget which i think all musicians should have , especially if gigging with vintage amps..
Even if it isn't the problem , its cheap insurance.

 

[Guitar-Rocker]

Hey, thanks for the speedy replies.

Mickeydg5, I measured the impedance from my speaker cable while plugged into the left jack on the cab and it was measuring 3.8 ohms. I took off the back piece and took a few pictures. Not sure if I connected the black's and red's improperly or if the polarity matters.

It is a genuine speaker cable, it's a Yorkville sound 18/2 GA speaker cable. It's a fairly new cable, I'm pretty sure I bought it earlier this year.

Should I test the impedance of each individual speaker?

I've had my selector switch (4ohms/8ohms) set to 8 ohms with my speaker cable running from the left jack on the cabinet to the right speaker outlet on the amp. Which has always been my norm for setting the speaker cable up with the amp and I've never had this consistent problem before.

The fuse that blew was rated for 250V 1A.

Your cabinet should not read 3.8 ohms. Start there.

 

[mickeydg5]

He said he had an 8 ohm amplifier impedance set for a 4 ohm cabinet impedance. Did no one notice that?

Jackson, that is not good.

It should be 8 ohms to 8 ohms.

 

[Ken]

He said he had an 8 ohm amplifier impedance set for a 4 ohm cabinet impedance. Did no one notice that?

Jackson, that is not good.

It should be 8 ohms to 8 ohms.

THERE's your problem!!! LOL Yes, a 100% mismatch on a Marshall can do quite a bit of damage. The OP should feel fortunate he's just blowing fuses.

Ken

 

[ampmadscientist]

Hey Jackson , I had a similar experience in a house i just moved into.
this land lord seemed to do his own electrical wiring . needless to say he got it wrong . any how , any thing i plugged in at one end of the house either tripped a breaker or fuse after a short ,,, time . I found the problem with a Wall outlet phase checker . It also lets you know if there's a ground problem, looks something similar to this gadget which i think all musicians should have , especially if gigging with vintage amps..
Even if it isn't the problem , its cheap insurance.

The best advice possible. Carry one of the testers in your guitar case.

USE the $10 tester!
Make sure the wiring and ground are good before using the power.
It "could" save somebody's life, no joke.

 

[mickeydg5]

Your cabinet should not read 3.8 ohms. Start there.

He is reading DCR with a multimeter. It seems about right for a 4 ohm cabinet and speaker cable.

 

[Guitar-Rocker]

I mentioned that based on looking at his wiring photos, but for a 4 ohm load, then yes I agree.