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Finally got to replacing the four diodes D5 - 8, and it has been running for 30 minutes, so maybe that got it. I ran it for 3 hours and then 2 hours before it came back, so I'm not taking a victory lap just yet.
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If replacing the diodes initially restored performance, and these diodes tend to fail the joints due to heat, but this is "normal" for the amp (?) I might try elevating the diodes as high as possible on their leads. But examination of the replaced diodes connections is necessary to determine this."Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
You can't just expect consent." HelmholtzComment
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The diodes were not replaced initially, they were removed and measured good and re-installed. The amp worked for 3 hours after that, and then 2 hours the next day, so I sent it home. It failed later. I replaced them this time, and so far it has been running for 3 hours last night, cooled down overnight, and is running for 4.5 hours again today. I did elevate the diodes a bit off the board, but more so due to it just being easier due to close proximity to the snubber caps.
I think this problem is solved.Last edited by Randall; 01-31-2020, 09:01 PM.It's weird, because it WAS working fine.....Comment
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I have exactly the same issue on my bench. I have disconnected the HT supply wires from the board and the board has only the 6.3v connected to it. all other plugs including the ones to the FX board disconnected. With the 12ax7s in sockets they heat up then the voltage suddenly drops and I can hear a relay click, then after a while the cycle starts again. I am trying to get info through a Marshall distributor here in New Zealand.Comment
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