16-01-2017, 11:53 AM
Hi Hayden / Lou,
I have made some progress, but not all of it is good!
My D-3800 went back into fault mode shortly after I posted the (IC2) LM723 "normal" pin voltages, and no amount of heat from my heat gun would persuade it to recover, so I have not been able to measure normal voltages for IC2, which is an LM339 quad comparator.
What I have ascertained, however, is that as expected the problem is in the LM339 area. When I disconnected one end of D12, which is connected from the open collector output of IC2D to the Remote Shutdown pin of the LM723, full output is restored. The D-3800 works perfectly, but of course without the protection afforded by the LM339 circuitry. That is not to say that the unit is totally unprotected - the over-temperature fan still works, and presumably the LM723 current limiting still works also, but I have not analysed that yet.
Hayden,
If your problem is in the LM339 area, this "fix" will work for you too, but I would not want to be responsible for suggesting it as a permanent solution. Lifting one end of D12 will be useful, possible indispensable, for diagnosing the problem however, as it restores power to the LL339 area, so that you can check voltages. I have been doing that, and so far I can only say that I am confused!
Best wishes,
Lew.
I have made some progress, but not all of it is good!
My D-3800 went back into fault mode shortly after I posted the (IC2) LM723 "normal" pin voltages, and no amount of heat from my heat gun would persuade it to recover, so I have not been able to measure normal voltages for IC2, which is an LM339 quad comparator.
What I have ascertained, however, is that as expected the problem is in the LM339 area. When I disconnected one end of D12, which is connected from the open collector output of IC2D to the Remote Shutdown pin of the LM723, full output is restored. The D-3800 works perfectly, but of course without the protection afforded by the LM339 circuitry. That is not to say that the unit is totally unprotected - the over-temperature fan still works, and presumably the LM723 current limiting still works also, but I have not analysed that yet.
Hayden,
If your problem is in the LM339 area, this "fix" will work for you too, but I would not want to be responsible for suggesting it as a permanent solution. Lifting one end of D12 will be useful, possible indispensable, for diagnosing the problem however, as it restores power to the LL339 area, so that you can check voltages. I have been doing that, and so far I can only say that I am confused!
Best wishes,
Lew.