1. RUSHFANnLV

    RUSHFANnLV Member

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    I turned on my Marshall 4140 today to let it warm up and when I went to switch the standby off....nothing. I checked all the connections and they were fine. Then I realized that the tubes weren't even glowing. I quickly switched receptacles to see if the outlet was the cause and...nothing!

    Checked the fuse and it seems to be fine. We were up and running yesterday without a problem. Any ideas? What could I have done wrong? I'm taking it in straight away tomorrow but I want to know what to expect. I'm crused.
     
  2. doc

    doc Member

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    Sometimes several outlets are on the same GFCI circuit, so it could still be the outlet.
    If the fuse is still okay it may well be just a loose connection somewhere. Sometimes with the modern amps the IEC power cable gets a little loose but still looks plugged in - I'd check that well. You could also have a power switch that isn't making contact. If it was working fine and the fuse is intact chances are good its something minor and easily fixed, so take some deep breaths.
     
  3. RUSHFANnLV

    RUSHFANnLV Member

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    Check three seperate outlets in the house, none of them being GFCI and still nothing. Yeah the fuse is fine so I'm hoping it is just something with the switch. The light never worked in the switch but I'm sure that has nothing to do with it. Thanks for the reasurance.
     
  4. Wakarusa

    Wakarusa Member

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    Which 4140? The earlier JMP 4140 has no fewer than 10 fuses in it, including a pair of fuses in the heater strings. The later JCM800 has two fuses (one for the 120V mains, the other in the B+ line).

    Anyhoo, you say the tubes aren't lighting up... does the power switch light up? And, finally, how did you check the fuse? I've seen lots of folks do only a visual inspection -- and the fuse can be blown and still look just fine.
     
  5. RUSHFANnLV

    RUSHFANnLV Member

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    WOW! That's good to know. I think this is a 1978 so that would make it one of the earlier ones. And yes, I did just do a visual inspection so maybe that is it. Would fuses cause the power to not even come on at all? And to answer your question, the light in the switch was out when I got it but the amp worked fine.

    Thanks! I'm going to download the schematic and take a look for the other fuses.
     
  6. Wakarusa

    Wakarusa Member

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    If the mains fuse is blown you'll get nada from the amp. Zip. Nothing. Replace with a known good or check the existing one with a multimeter or continuity checker. I agree that '78 would be the JMP model. Most of the fuses are internal, so you have to pull the chassis. All of the standard precautions about electrical death apply. If one of the fuses in the heater string is blown you'll usually get no output from the amp. All 10 fuses may or may not be present -- don't sweat it if one or two are missing. You can also get replacement switches so the light'll work again ;)
     
  7. RUSHFANnLV

    RUSHFANnLV Member

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    Right on man. Thanks a million. I'm going to leave all this up to a pro so it will be Monday before I can take it anywhere. I wanted to get the power tubes replaced anyway.

    Thanks again. I'm glad to know that it's probably just a fuse.
     
  8. RUSHFANnLV

    RUSHFANnLV Member

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    Well I got a meter on the fuse and the main fuse is just fine. It must be one of the other fuses or the switch. This stinks but I guess that I'll have to get use it if I'm going to be using vintage gear.
     

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