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  1. #1

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    Unhappy The last of the magic smoke

    Came home from work yesterday and noticed the LED's in my PassDiy F5 amplifier weren't lit. Still plugged in, breaker wasn't tripped, switch on; something was amiss. After dinner I opened it up and the fuse was blown, didn't see anything obviously shorted or damaged so I replaced the blown fuse. Powered it up and within a second or two the fuse blew again, the last remaining magic smoke releasing into the air from the left channel.

    I swapped in another amp so I've got tunes; the old Rotel in the F5's place actually sounds a bit better , which leads me to believe that the F5 had been sick for a bit. I'd noticed a hum from the left channel recently as I worked on the bathroom adjacent to the left channel's speakers. I dismissed it, thinking I was focused in on the hum because everything was annoying me as I was having trouble figuring out a plumbing issue.

    Not really sure what I'm going to do at this point. Looking at the amp boards themselves, they aren't my best work. Power supply, wiring, and chassis construction I am happy with. I could get my father in law to help me fault trace the issue and repair the amp, but some of the components in the F5 are getting very difficult to find, and must be matched with one another, which translates into a significant outlay money wise. On the other hand, the cool thing about the Firs****t clones is the power supply and heatsinks are universal throughout the line. diyAudio has a webstore now selling boards for a few of the PassDiy and Burning Amp designs with plenty of documentation. It would be pretty simple to pull the F5 amp boards out and replace them with an Aleph J for example.

    Anywho, guess I was just feeling a bit bummed this morning. It was my first amp that I'd built, also the first audio project I'd completed without having a kit. Felt pretty proud that I'd been able to sift through the F5 thread and come out with a working unit. Guess it's just a good reason to have another project...
    Wris****ch--->Crisco

  2. #2

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    Sorry to hear that Ben. Transistor/jfet matching is easy if you have a curve tracer...only a few hundred to lots more dollars...lol I have a project where I need to build a test circuit and use a DMM to grade and match.

    Anyway, since it won't power up and unpowered in circuit testing isn't accurate you have to remove things to test like jfets, transistors, etc. Resistors and caps you can desolder and remove one leg to get accurate readings.
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  3. #3

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    Thanks Rich.

    It really happened at the best time, was just getting ready to make some system changes with the F5 as the foundation. If this had happened a couple weeks later it could have been much worse.
    Wris****ch--->Crisco

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    Sorry Ben, but the Aleph J would be cool and nice consolation.

    Good luck

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

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  5. #5

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    That blows.You might want to disconnect the power supply from the amp section and see if it powers up fine.Then you can at least know if it is supply or amp board related.

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    Ben, I'm sure you'll get the magic smoke back in that amp :)
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  7. #7

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    I never replace a fuse when I see one blown until I check out the amp and see if any parts are shorted out. A dead fuse is a warning that more damage is coming your way more times then not.

    Seen a guy working on a TV which keeper killing the fuse he got mad and installed a 20a slow blows
    And let's just say the smoke was replaced with fire but it was fun to watch.
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  8. #8
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    I agree with Fred. Test each part independently as a start, and hopefully that will point you in the right direction.

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    Sorry for the amp troubles Ben. I hope you get it solved and I suggest you use the Aleph J boards as replacements (as you suggested).
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  10. #10

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    Quote Originally Posted by FTGV View Post
    That blows.You might want to disconnect the power supply from the amp section and see if it powers up fine.Then you can at least know if it is supply or amp board related.
    Quote Originally Posted by zingo View Post
    I agree with Fred. Test each part independently as a start, and hopefully that will point you in the right direction.
    Good thinking, guys. Will definitely try that when I get a chance.
    Wris****ch--->Crisco

  11. #11

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    I'm very sorry to hear about your amp trouble Ben, hopefully when you get some time , you can fix her and get that pup up and running!

  12. #12

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    Over the weekend my father in law was over and he helped me poke about a bit. With a couple of multimeters and 15 minutes away from my son's birthday party, we came up with a fairly likely scenario. The input wire (unshielded) on the left channel had come loose from where it was mounted in the chassis and came to rest within 1/2" of the left channel output wires (also unshielded). This caused the channel to oscillate, burning out at least both MOSFET in the left channel over some period of time. Looks like the amp board sustained some damage as well.

    At this point I don't think trying to fix this is meant to be. I did come across some F5 boards that I'd forgotten about, but I'm not thrilled with their layout. The Aleph J is interesting, but need to see if parts are available. I might have enough transformer and heatsink for an F5 Turbo, come to think of it though...
    Wris****ch--->Crisco

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