I have tried to attach a schematic.
This amp has a CPU which keeps powering off the unit. When I power the unit it starts and makes 65volts + & - about 5 seconds later it shouts down. In the diagram Q20 & Q21 are part of the Protect circuit and Q21 stays at 5V. Q20 has 65volts on the Base and Emitter and .001volt on the collector. I also replaced the 5.1 zener although it checked out.
There is .04 volts at the most on the outputs but I don't think that would shout it down. I did find diode D32 across the relay to be shorted and replaced it. I have also pulled all outputs and checked them ouyt of the board(they were fine).
Please help me with any ideas.
Thanks Jeff
This amp has a CPU which keeps powering off the unit. When I power the unit it starts and makes 65volts + & - about 5 seconds later it shouts down. In the diagram Q20 & Q21 are part of the Protect circuit and Q21 stays at 5V. Q20 has 65volts on the Base and Emitter and .001volt on the collector. I also replaced the 5.1 zener although it checked out.
There is .04 volts at the most on the outputs but I don't think that would shout it down. I did find diode D32 across the relay to be shorted and replaced it. I have also pulled all outputs and checked them ouyt of the board(they were fine).
Please help me with any ideas.
Thanks Jeff
I don't have the manual for the 401. Using the manual for the 201, there is a transistor connected to the positive rail that drives the protect input of the processor. The 5.1v Zener is used to limit the voltage sent into the input of the processor. If you remove that transistor, the amp shouldn't be able to go into protection and you should be able to troubleshoot the problem.
When the protection circuit is disabled, you must be very careful/observant. You should have the power semiconductors clamped to the sink and you must monitor current draw. You should have a current limiter on the B+ supply line. If there is a real fault causing the amp to go into protection, it's possible that damage can occur very quickly if you're not careful.
When the protection circuit is disabled, you must be very careful/observant. You should have the power semiconductors clamped to the sink and you must monitor current draw. You should have a current limiter on the B+ supply line. If there is a real fault causing the amp to go into protection, it's possible that damage can occur very quickly if you're not careful.
Hate to bring this one back from the grave. Buuuttt.... I am repairing 401m. I've had it for a while (Years) and have just gotten back around to it. This one is a weird one and Im at a loss. I am thinking that the main IC (IC2) may be faulty.
Checked the power supply and output transistors and all check out fine.
I removed Q20 and Q21 because I couldnt get the amp out of protect. Verified that there was not 5v going to pin5 but the amp is still in protect.
Applied 12v to the pwm IC and the power supply powers up fine. Verified a nice solid +/- 62v and 15v rail. Amp pulls a low 2 -3 amps at idle.
Everything outside of IC2 seems to be functional. It just thinks something is wrong for one reason or another. Im almost tempted to short the emitter and collector on Q22 to get the relay to turn on to see if I can get audio out of it.
Any suggestions are greatly appreciated and thanks for you help~
Checked the power supply and output transistors and all check out fine.
I removed Q20 and Q21 because I couldnt get the amp out of protect. Verified that there was not 5v going to pin5 but the amp is still in protect.
Applied 12v to the pwm IC and the power supply powers up fine. Verified a nice solid +/- 62v and 15v rail. Amp pulls a low 2 -3 amps at idle.
Everything outside of IC2 seems to be functional. It just thinks something is wrong for one reason or another. Im almost tempted to short the emitter and collector on Q22 to get the relay to turn on to see if I can get audio out of it.
Any suggestions are greatly appreciated and thanks for you help~
Please don't post in a repair thread that was started by someone else unless you are trying to help them.
Start a new thread if you need help with a repair of your own.
http://www.bcae1.com/temp/newthreaddiy01.png
Start a new thread if you need help with a repair of your own.
http://www.bcae1.com/temp/newthreaddiy01.png