01-02-2017, 03:37 PM
Hi Hayden,
Thanks for the update, and well done on diagnosing a difficult intermittent fault. I think I got lucky when my intermittent fault became more permanent. I can see that VR2 going high in value could indeed trigger the overload signal, and it is a very plausible intermittent fault. How did you adjust VR2 after replacing it?
Fitting a crowbar seems like a good insurance policy. It would be interesting to see whether one could get away with something less than a 5 A fuse on the 240 V side, in order to minimise the crowbar current.
I also got lucky with the second D-3800. The LM723 had failed. I think I must have shorted a couple of pins when measuring the pin voltages. I have used a socket for the replacement LM723, and I'm replacing the component-side electrolytics before putting it back together. This time I will remember to recalibrate the Voltmeter while it is still accessible!
Best wishes,
Lew.
PS On the second unit, it was very hard to separate the PCB from the 5 mm terminal posts. I had to de-solder around the posts before it would let go. I will filing out the holes a little before reassembly.
Thanks for the update, and well done on diagnosing a difficult intermittent fault. I think I got lucky when my intermittent fault became more permanent. I can see that VR2 going high in value could indeed trigger the overload signal, and it is a very plausible intermittent fault. How did you adjust VR2 after replacing it?
Fitting a crowbar seems like a good insurance policy. It would be interesting to see whether one could get away with something less than a 5 A fuse on the 240 V side, in order to minimise the crowbar current.
I also got lucky with the second D-3800. The LM723 had failed. I think I must have shorted a couple of pins when measuring the pin voltages. I have used a socket for the replacement LM723, and I'm replacing the component-side electrolytics before putting it back together. This time I will remember to recalibrate the Voltmeter while it is still accessible!
Best wishes,
Lew.
PS On the second unit, it was very hard to separate the PCB from the 5 mm terminal posts. I had to de-solder around the posts before it would let go. I will filing out the holes a little before reassembly.