|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|
A backup power supply is a handy thing to have around. You can stay on the air if your main supply take a vacation. (Or you can do like I do, and use the second supply as a justification for buying a second radio.)
I’ll agree on Digi-Key. I had an opportunity to take a tour of their warehouse a few years ago in Thief River Falls. It’s incredible that they have millions upon millions of part numbers that all get picked, packed, and on the truck in under 20 min from the moment you finalize your order.
On Astron power supplies it’s a good idea to cover the cases of the power transistors so that something (cable being dragged around) doesn’t short them to the chassis – which, even though you cut the jumper, *will* be tied to your negative ground lead through the 3rd prong on the AC cord and your radio’s chassis.
Another thing to consider is that there may be an exposed stud on the back that is at the supply – or raw (pre-regulator) voltage: This is certainly true of the RS-50 – maybe others – and should be checked out. All of them that I’ve seen have exposed voltage that, accidentally shorted, will probably blow the rectifier.
The above issues “bit” me once at a mountain top repeater site that used a modified (to “auto reset” itself) Astron: When running coaxial cables, one of them touched a exposed transistor collector on the heat sink causing a big flash and blowing up the bridge rectifier – and an unexpected return trip a few days later with the repaired supply that now had properly-covered devices.
Yes be careful with those transistors on the back of the unit. I had a bad experience when a coax cable connector got to close and shorted out one of the pass transistors. It made a big hole in it. I told myself to be more careful and change out the transistor. All was ok after the repair. I saved the story and transistor for show and tell at our next club meeting. Always learning something!
Good evening Dave thanks for taking the time to leave a comment, I was thinking the same as well Dave in regards to having an extra power supply for the just in case moment. I just can’t count the number of times I have had sold something to only realize later I in fact needed it. As for the second radio, I have an Elecraft KX3 that I use for portable and if the Icom has to go out for repair it will be my backup radio.
Dave have a good what is left of the week.
Hello Bob very nice to hear from you, I was just amazed at the fantastic service I received from Digi-key and I have been waiting for an email to ask me for my feedback but nothing yet. I was very impressed with an email very shortly after ordering the parts that my order has been picked and has been shipped. This facility to had taken a tour would be very very impressive. Thanks for your input Bob and have a great week.
Hello Clint, I had no idea that the pass transistors could have such an issue and it’s good to know this could be an issue. I did try to look on the internet for ideas on how others have covered the pass transistor but was not able to see anything. This makes me much more aware of the rear of the Astron supply and what could happen if am not careful.
Thanks for the great info Clint.
Top of the evening Lyle and nice to hear from you, I only can imagine the surprise when you heard the pop sound. I would imagine there are lots of Astron power supply owners out there that have no idea this could happen. I know I was one up until this last post regarding my power supply repair. Thanks for the info.
Jim Brown, K9YC, has written extensively about killing noise in your station.
see slide 138 here: http://audiosystemsgroup.com/GroundingAndAudio.pdf
and this: http://k9yc.com/PowerSupplyBondingAndAudioDistortion.pdf
You be the judge. I can tell you that after reading these articles, I broke the V- to green wire bond, and sanded the paint away from where the safety ground (green wire) is attached to the chassis on every astron that crossed my bench.
As for your RS-20, KEEP IT! it is a good supply to run your QRP gear or FM mobile rig.
Wow – I hadn’t considered the exposed transistor on the back of the power supply being “hot”. That’s good information! Does anyone have a suggestion for covers for these?
Good evening Mark and an excellent question I was thinking the same as well. I did look online to see if there was anyone who posted a writeup or a picture but I found nothing. I was thinking that it had to be something that insulated but at the same time not stop the transistor from dissipating heat. I would imagine there is something out there and I have been thinking about it off and on. If I come up with anything or if I get some outside information on it I will for sure at a post to the blog about it.
So anyone out there who is reading this post has an idea or in fact, has isolated the pass transistors do tell.
Thanks for the comment Mark
Good evening Jeff thanks very much to the links they both were a great read. K9YC really gets into detail and it’s also good he named names of both the good and bad commercial gear.
Thanks for the info