my JCM900 is dead

[cris9288]

ok here's the story. i've had this JCM 900 for about three months now. it's worked fine. the only thing i did was change the tubes. the owner before me, had if for about 7 years. he bought if from a Guitar Center somewhere in Southern california.

Just the other day, the amp stopped working. I turned on, and after some loud humming, thirty seconds later the amp shut off. No power at all!! So i took to a music store right away.

they call me a week later and tell me that i have a european amp, made to run on 240 volts. and that's why it won't turn on. it blew the fuse inside. My first thought was "that's impossible. it says 120 V on the back, and the power chord is 120 V, and i've been using it for some time now here in the states."

So i brought it back and replaced the fuse. First i put in a 250 V 2A fuse, it blew that one after about three seconds of having the power on. Then i put in a 125 V 4A fuse. This one blew, the second i plugged in the power chord into the back of the amp. Right above the mains input, there's a little decal that says 120 V. but after a lot of work, i scratched it off (it was on there real well), to reveal 240 V.

So can someone help me? did my amp change nationalities overnight? is it something else? any help would be great, thanks!

[Twist]

Did the amp sound fine before and if so how long did you have the amp. Regardless of the confusion on the mains voltage something has shorted in the amp. I would first take out the output tubes and replace the fuse and power up. If it powers up then you need to take some readings from the pins in the output tube sockets. This should tell you if you have an import tranny. Newer Marshalls can be rewired for domestic use.

[stokes]

If as you say it worked fine for 3 months I have to doubt it has an export tranny.Time to find a new tech.

[cris9288]

twist: it's worked here in the US for a long time before i had it, but i've had it for three months now. and yes it's worked fine. i'll probably take it to another tech like the other guy suggested, since i don't have the tools or the confidence to do all that stuff you said. but yeah hopefully it's not an import, and it's just a shortage.

[Twist]

Sounds like a wise choice. Just have the new tech make that someone didn't inadvertently rewire your tranny for 240. Good Luck..

[cris9288]

^if someone did rewire it, it would've had to have been overnight while i was sleeping, cuz i was playin it one day, and the next day it just went bad. I had it in my bedroom, but then i moved it out to my living room cuz i wanted to record in a bigger room. maybe while i was movin it something got messed up inside, idk, but anyways, thanks.

[52 Bill]

Cris:
First off, don't believe everything that someone in a store tells you. I don't know how qualified the person was that told you that your amp was wired for 240v, but logically and technically, if you've been using the amp here in this country it would be very unlikely for that to be the case,. Some Marshalls do have a transformer that can be wired for either 120 or 240, but it would not have worked for you if it was mis-wired before you took it in to the store.

Second, blown fuses are very typical of shorted output tubes. If you want, pull out all of the large tubes - 6550, 6L6 or EL-34 are the typical tube numbers, and then try the amp with a new fuse. If the amp stays on, then you know the tubes are the problem. If the fuse still blows, then you still have an internal problem that you will need to address, like a shorted rectifier diode or something.

In either case, you need to take the amp to a different tech for a correct analysis.

[Chuck H]

Take it to another tech and ignore what the other guy said. If your amp was actually wired to run on 240v it would not likely work at all on 120v. The fact that it worked fine for so long is all the evidence of that you need. If it is an import tranny then it is now wired for 120v. So the amp is now designed to run on 120v.

If your not interested in opening it up yourself, take it to a proper repair shop. It's probably a bad tube. But the amp should be opened up anyhow to check for charring and burned componants.

Chuck

[cris9288]

well thanks guys. the tube thing makes sense, since when i moved it from my room to the living room. i move it a lot, but i just might've gotten careless this time or something. but yeah, that's why i brought it back, cuz it didn't make it sense that if it worked for so long before, it was suddenly an import tranny. i mean how does it rewire itself overnight? anyways, thanks for the help everyone.