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Fuse blows when speaker is connected. |
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spacebiscuit 
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Joined: 28 December 2023 Status: Offline Points: 28 |
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 Topic: Fuse blows when speaker is connected.Posted: 19 May 2024 at 11:34pm |
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Hi All,
Quick question - Mosfet amp powers up ok, but as soon as I plug the speaker to the output jack of the amp a fuse blows. Without the sepaker connected the fuse does not blow. It looks like it is fuse for the + side of the power supply and N-Mosfets. Does that sound correct? Any suggestions where I should start my troubleshooting? TY.
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Earplug
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Joined: 03 January 2012 Location: Europe Status: Offline Points: 7752 |
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Posted: 20 May 2024 at 6:22am |
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Sounds like you have 1 or more blown output device. Desolder the legs of the devices and check for continuity between them, What amp is it? |
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Earplugs Are For Wimps!
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spacebiscuit
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Posted: 20 May 2024 at 10:45pm |
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Mosfet T-400 Power Amp - looks very home brew - I can't find any reference to it online.
The N-fet - when out out of circuit there should be continuity with DMM from Drain to Source if i understand correctly since the circuit for N-fet is normally closed. Have I got that right?
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Earplug
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Posted: 21 May 2024 at 6:32am |
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Yes, Drain to Source will act like a diode, i.e. continuity in 1 direction. Just desolder the legs and check all. If blown, it will be fairly obvious. |
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Earplugs Are For Wimps!
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spacebiscuit
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Posted: 21 May 2024 at 6:57pm |
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Hmm, i de-soldered the N-Fets and they test ok in my component tester...
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Earplug
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Posted: 21 May 2024 at 7:22pm |
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Check the P channel FETs as well? Or post some photos. An image is worth ...  |
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Earplugs Are For Wimps!
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kedwardsleisure
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Posted: 21 May 2024 at 10:23pm |
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sounds like the amp has gone DC. Test for dc voltage at the speaker outputs (speakers not connected of course).
If thats the case then it could be any component on the board TBH |
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Kevin
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spacebiscuit
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Posted: 22 May 2024 at 11:26pm |
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Removed the P-Fets - also tested ok. Did find a suspect bit of soldering which may not be helping matters. I'll check for the "DC" tomorrow when I try to power it up again - will update.
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spacebiscuit
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Posted: 30 May 2024 at 7:15pm |
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Does anyone know how to test this cut-off board?
To give the full back story. My 1st post in this thread was about channel 'A' which blew a fuse whenever I connected a speaker. Prior to this Channel 'B' blew both P-Fets and the resistor on the cut-off board - see the new green resistor and the burned pcb. When this happened and I changed that resistor and I tested it by wiring it up to Channel 'A' and just powering the amp up - all seemed ok. Likely not connected but when I later went to use the working channel 'A' it blew the fuse when speaker was connected (post #1). As mentioned in my last post, Channel 'A' seems ok now after I resoldered a few components - all working fine wit output. Now to - Channel B, I've added some new P-Fets but before I power it up I want to ensure that the cut-off board is ok - is there a way to test it? There are 3 wires that are marked "in", "out" and "0v" on the board and each one is soldered to a different resistor. Any thoughts?
 Edited by spacebiscuit - 30 May 2024 at 7:18pm |
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