Crown D-45 Amplifier

[pb]

My monitoring amplifier has started to distort continually on one channel, i have swapped the inputs around, and it persists on the same side.

The IOC led is also flashing, confirming the distortion.

I have been reading the  service manual for its sister product, the D-75.

Slowly i am beginning to build a picture of this unit in my mind, but its hard work so see it clearly.

Can i make some simple measurements to try to pinpoint this fault? or at least get closer to it.

Any advice would be much appreciated.

service manual is here.  http://rdn.harmanpro.com/product_documents/documents/3603_1438110698/Copy_of_D75_Service_Manual__original.PDF

 

[JohnRoberts]

If you have one working channel and one faulty you might carefully measure and compare voltages but that may not isolate exactly where the fault is.

The IOC is telling you what you already know, but the IOC looks at the amplifier NF node, and if the global control amp is able to control the output voltage that NF node will be 0V (same as + input). So the fact that the amp is not controlling the output means the fault is somewhere in the output stage between control amp and final output.

Perhaps with power off, measure all the active device transistor junctions looking for a device that is faulty (you should measure a diode junction -approx 0.6V from base to emitter and base to collector in good devices. 

JR

 

[pb]

John, thank you for the advice,

i ended up making a home-brew (twin LED style) transistor tester.

found the culprit, & all is now good again.

best

Pb