Power supply failure!

Dusty but looks ok 

I got up Saturday morning with plans of getting on the air and participating in the CQ Worldwide CW contest. Well that was the plan and I did get one contact in the logbook but as I was working the second contact my power supply made a thump followed by my Icom 7610 abruptly powering down. When this happened it left me with a bad feeling and an uneasy understanding that the contest for VE9KK was done! I was hoping that for some reason the crowbar protection kicked in and I would just be able to restart the power supply and all would be well. That was not the case my Astron RS-20M was dead in the water. I checked the 5 amp inline glass fuse and it was blown catastrophically. I replaced the fuse

and turned on the power supply hoping for the best and the best did not happen, the power supply did not turn on and I found this new fuse had blown as well. One thing was for sure and that is the CW Worldwide CW contest was over. My thoughts were on the power supply and getting the cover off to see if anything was obvious as to what the issue was that I forgot about my Icom 7610. It was about an hour later it occurred to me......"did my 7610 suffer any damage?" Since my power supply was out of service I had to come up with another way to power up the 7610. I decided to use the battery that is used with my Elecraft KX3 for outdoor op's. I connected it up and pressed the 7610 power button and NOTHING happened!! I just felt sick at this time, my brand new Icom 7610 also took the hit as well? I was thinking about checking the Icom 7610 inline fuses to see if they saved my rig by taking the fault? I decided to take a break and do some thinking and I was glad I did. On my return to the radio room, I decided to check the battery voltage and low and behold it was at 10 volts and the Icom needs 12.7 volts DC to power on. I charged the battery ( that was the longest hour ever!!) and tried again and thank goodness the Icom powered on. It was now time to get back and troubleshoot the Astron power supply. It was now time to see if there was any visible damage to the internals of the power supply?

 I was not able to see anything in the power supply with a visual check. Checking the schematic diagram I checked out the power on switch and it was good, next

Bad Varistor  

was the varistor if it was shorted that would cause the fuse to blow. I found the varistor to be open, this is not good and I have to replace it but this would not cause the fuse to blow. I then disconnected the secondary transformer connections from the bridge rectifier I then replaced the inline fuse and powered up the power supply. Everything was good and this was great news as it was not an internal short in the transformer. I then connected the transformer to the bridge rectifier and powered up. The inline fuse blew as soon as the power supply was turned on. I then removed all connections to the bridge rectifier leaving the

Shorted diode 

AC transformer input only, once I powered up the Astron the inline fuse blew again. It was time to investigate the bridge rectifier and see what was up. The investigation showed a short in one of the diodes in the bridge. At this point, I am replacing a thyristor and a bridge rectifier. Next in line are 2 transistors but time was not on my side and that is going to have to wait until Monday to do.