Potential Astron power supply failure solved!

One of my blog readers informed me regarding the Astron linear power supply that the outer case on the pass transistors at the rear of the supply are live with about 24 volts.  These pass transistors are isolated from the case and the heat sink so the potential is there to inadvertently via a PL259 connector, USB cable or any other conducting item at the rear of your setup to short the pass transistor and destroy them.  This morning I once again was searching the internet to see if anyone had devised a solution for this very issue. I came across a web page . This individual has the RS-35A power supply and came up with a great solution using a 3D printer. Now I am not at all up on the whole 3D printer thing but click on the link  above (web page) and have a look at the pictures they posted. The covers look great and are very professional looking. It would look to me the plans are available to those who have access to a 3D printer to produce the guards them self.  I would really like a set of these for my RS-25 but just short on the 3D printer part of things.
To my fellow bloggers have a look at the above link and do post any 3D printer info you may have as well.

As a side note below are some links to great information regarding Astron power supplies.

http://www.wb1gof.org/files/AstronPDF.pdf

http://www.repeater-builder.com/astron/pdf/astron-troubleshooting.pdf

http://www.repeater-builder.com/astron/astron-repair/astron-repair.html

https://www.ecse.rpi.edu/courses/CStudio/ham_radio_docs/astron-repair-index.htm

The Astron SS-30M power supply.

I picked up the new power supply last week on Friday from the post office just in time for the CQ WW CW DX contest. The power supply I ended up choosing was the Astron 30 amp switching power supply. Yes I wandered away from the linear power supplies and into the dark side of the switching power supplies. The supply had very good reviews and now that I am on a fixed budget the linear supplies were just a bit to high for the budget. I have been using this supply for over a week now and am very pleased with it. There is no"hash" from this supply that I have read about online with other switching supplies. I have used it in the CW contest and also this week on FT8 and it has not heated up at all. After repairing the Astron RS20 I decided to keep it as a back up supply just in case the new supply in the future lets me down.....BUT when I do use it I will keep its duty cycle in line to what it has been designed to handle and not what I was putting it through.

The Astron RS20-M repairs completed

Repaired and working

The repairs to the Astron RS-20M are complete and the power supply I am happy to say is back up and running. In the process of sourcing out the parts that I needed a reader of my blog gave me a glowing recommendation of Digi-Key Electronics. I am very glad that he gave me the heads up regarding this company. When I went to the site you have the option of chatting live with an agent if you have any questions. I took advantage of this several times as I wanted to make sure I was choosing the correct items. The order was placed with them and immediately I received a

Negative to case ground 

Confirmation email regarding the payment going through. Within an hour another email was sent informing me my items had been shipped along with a tracking number. My dealings with Digi-Key was outstanding, I had recently dealt with an Amateur radio store up  this way (when ordering my new Astron power supply). The only email I was sent informed me my order had been processed and that was it. I wondered if just the payment went through, if the order had been picked and or if the order had been shipped? I ended up calling them to see if it had been shipped I asked when I may expect it to arrive, so I would make sure I was home as it needed a signature. The person on the phone sounded very put out as it required them to do some digging. They did return to the phone informing me it had been shipped and should be here by Friday. When I asked for the tracking number I was told it was not store policy to give out this information?? The power supply ended up coming on Thursday, and I was not home which required me to make a trip to the post office on Friday to sign and pick it up. Let me get off my soapbox and get back to the power supply repairs.
I found this great site online regarding Astron power supply trouble shooting and repairs. This document really helped me with the trouble shooting and eventual repair of the power supply. There was another online article I came across regarding how Astron now and then has the negative terminal grounded to the case of the supply.

New bridge rectifier

The part that I had to replace was the Bridge rectifier but I also ordered some heat sink compound as this was used between the Astron case and bridge rectifier. I also removed the two pass transistors and replaced the heat sink compound there as well. As mentioned above some Astron power supplies have a wire going from the negative terminal to the case ground. I read the information (seem link above) regarding Astron sometimes grounding the negative terminal to the case of the power supply. My power supply was wired this way and I decided to remove this jumper wire, if you have the same situation with your Astron supply read the article via the provided link above and make your own decision.
With the new bridge rectifier installed and wires re-soldered, the pass transistors back in place and finally I did remove one connection of the Varistor to test it (tested ok) I had to also re-solder that back on as well. It was now time for the smoke test.......and I was pleased that no smoke was found and the power supply is now working without issue. I did connect it to the Icom 7610, adjusted the power to 50 watts and the power supply successfully passed the load test as well. This power supply is under sized for the Icom 7610, I now have a new Astron power supply that is sized correctly. I am now wondering if I should keep this supply or sell it?

Passed load test

The power supply testing is done

Defective part 

The power supply troubleshooting is all done and tomorrow I will order the replacement parts, but first, there were two things I mentioned in the last post I wanted to correct........

1. I am recently retired and I was told you would slowly forget what day of the week it was, well that has not happened as of yet. I can say that with regards to ham radio contesting this retiree has mixed up what contest was on what weekend! In my last post, I had the idea of the CQWW CW contest was on this past weekend and in fact, thanks to my fellow bloggers I was informed it is next weekend. When I went back to the ham radio contest calendar site it sure was plain as day that in fact, it is next weekend. This is a good thing because my new Astron power supply will be here and I will be good to go for the contest.

2. In my last post, I indicated the varistor was defective and posted a picture of my Fluke meter indicating OL. DUH.....this is an indication the component is just fine!

Pass transistor testing 

Now the power supply troubleshooting is done and I have to thankfully replace only one component and again the failure of the power supply is my own fault. The power supply is an Astron RS 20M and it is rated at 16 amps continuous, this has been just fine when I was operating QRP at my previous  QTH. As my readers know I am now retired and have moved to New Brunswick and my new antenna is an Endfed. I have been raising the power output of the 7610 slowly and slowly but forgetting I am only using the RS 20M power supply!! The result was a failed power supply as it was just not rated for what I was attempting to do.  The new Astron power supply has a 25 amp continuous rating and the Icom 7610 is rated at 23 amps continuous so I will be good to go.

Back to the final power supply troubleshooting, I checked the 2 pass transistors and they both passed. I then checked the balancing resistors connected to the emitter of each pass transistor and they were both good. There were some capacitors that I also checked and they too passed. It seems that the only component I need is a bridge rectifier along with a tube of dielectric paste for the pass transistors and a new bridge rectifier. I am very happy the repairs are minor to the power supply.

Positive test results 

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.