diagrams for Fukai needed

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   I have a Martin Brothers MA4.2s which is a Chinese copy of Martin Audio. 
It failed and I fixed it but there is still a problem. 
The failed output stage is fixed, but the rail switch is stuck. It is not the mosfet, and I have replaced the chip driving that. 
The black paint on the board doesn't help, but it comes off fairly easily, still the circuit is nearly impossible to trace on a double sided board. 

Has anybody got any further info? 

The chip that drives the mosfet is a 555 timer in monostable mode. The problem appears to be in the signal triggering the 555 or the components around it. 

This pic shows the the heatsink assembly lifted and turned to show the output devices and the second shows the driver board.

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nev23 Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 08 September 2008 Location: Taunton, UK Status: Offline Points: 99	Post Options Post Reply Quote nev23 Report Post Thanks(0) Quote Reply Topic: diagrams for Fukai needed Posted: 23 May 2017 at 11:49am
	I have a Martin Brothers MA4.2s which is a Chinese copy of Martin Audio. It failed and I fixed it but there is still a problem. The failed output stage is fixed, but the rail switch is stuck. It is not the mosfet, and I have replaced the chip driving that. The black paint on the board doesn't help, but it comes off fairly easily, still the circuit is nearly impossible to trace on a double sided board. Has anybody got any further info? The chip that drives the mosfet is a 555 timer in monostable mode. The problem appears to be in the signal triggering the 555 or the components around it. This pic shows the the heatsink assembly lifted and turned to show the output devices and the second shows the driver board.