Adrian White

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About Adrian White

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  1. Sorry not to have picked up on this thread earlier. In my experience it is very very rare for an op-amp to fail on a D150/A or DC300A etc. It sounds more like a component deterioration problem within the current source for the voltage amplifier sections of which the 10uf capacitor (Circuit Ref. C5) previously mentioned is indeed part thereof. This is connected to the two small signal transistors that share a common heatsink on the PCB. The easiset thing to do is measure the DC voltage across the 10V zenner diode that this capacitor goes in parrallel with. This should be (not surprisingly!) 10V but I expect that it will probably be between 7 and 9 instead. If so, the best thing to do in my experience is to replace the 10uf 63V cap, the zenner diode and (if you can get a suitable one) the series 10uf 150V capacitor that feeds this network from the power transformer/rectifier (Circuit Ref. C4). The problem is a common one with DC300As that have been in service for some time but because the circuit is very similar on the D150/A it turns up there too. The Crown part numbers that I think you want are - C3728-0 10uf 63V Capacitor C2796-8 10uf 150V Capacitor C3549-0 10V IN916B Zenner Diode Good luck and I hope this helps Best regards Adrian