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Old 18th June 2012, 04:31 PM   #1
ClassA is offline ClassA  Taiwan
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Default QUAD 405 main board fuse blow

Hi,
My 405(1978 version) main board (one side) fuse blew when power is on. Anyone knows what happened?

Cheers
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Old 18th June 2012, 04:48 PM   #2
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Quote:
Originally Posted by ClassA View Post
Hi,
My 405(1978 version) main board (one side) fuse blew when power is on. Anyone knows what happened?

Cheers
Check out the power output devices Tr9 and Tr10 so as the driver transistor Tr8/Tr7 - go to
http://www.fralu.de/images/qaud405.jpg
Check out additional, whether the micas between the heatsink and the transistors are in good condition.
In case of failured BDY77 check the power amp in first step without Tr8-10 (i. e. only with Tr7, R30 and R31 - now only working as a single ended power amp with aprox. 20mW output power - i. e. very small output level, but enough for hearing).
After proper working in this mode you can risk the replace of the output power devices.
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