Repairing an Astron RS 35M power supply for HAM radios

does your astron power supply do this [Music] hi it's chris k2cjb with k2cjb radio welcome back to the channel i was operating hf a couple of nights ago and my power supply started humming like that and of course the first thing you have to ask yourself is why does a power supply hum probably because it forgot the words okay that's a bad joke and it's an old joke but anyway um i was tuning up the radio and then i was doing some ft8 and every once in a while this has been going on for a while i would hear a hum a little louder hum especially when it would transmit an ft8 i backed the power down on the radio thinking that was a problem but it never went away but what really concerned me was when i was operating sideband and i heard that hum loud when i was transmitting so it's time to take a look at the power supply and see what's going on the first thing we're going to do is take a look at the output voltage of the astron to see how that reacts with a load this is a little meter box that i put together some time ago the bottom meter lets me know what the ac power is that's feeding the shack the top two dc meters look at the two dc power supplies that i use um the top one is for the astron supply and the bottom one is for an auxiliary power supply that feeds all the accessories in the shack this little digital meter kit i got from my friends down at quicksilver radio and it really is a handy little tool to have the first thing we'll do is we will put the ftd x3000 into tune mode and see how the power supply reacts and as we can see the output voltage of the astron does not change that's a good sign that tells me that the regulator circuit in the power supply is functioning so now let's take a look at the ac ripple on the output of the power supply i've got the meter connected to the output terminals right on the back of the astron power supply and this is the output it's 13.6 volts to measure ripple we change the meter to ac mode and we're going to see a very low ripple at this point i would think we can change the scale of the meter so we get a little more of an accurate representation so that's what we have right now now let's put it under load we'll put the the fcdx3000 into tune we see an increase in ripple not a whole lot but we do see an increase in ripple and we definitely hear that hum at this point i suspect it's the filter capacitor in the power supply i just kind of suspect that you know a little more current being drawn through it if the capacitor is breaking down it's a good chance it might not be filtering as cleanly as it should be i can tell you that i've owned this power supply since 1998 it was the very first thing i purchased on ebay i bought it to run a yaesu ft-100 i can also tell you that this power supply since i've had it has been on turned on powered up 24 7 for pretty much the entire time there are a few times when i moved or i might have lived somewhere or i wasn't using the power supply but i'll tell you what for the most part that power supply has been turned on the entire time so i think it's a safe bet that something like the capacitor has failed so let's take it apart and see what we have to do there are three screws on the top that you have to remove and i've already done that then you have to flip the power supply over and remove the four screws on the bottom before going any further let's talk about a little safety here this is a large filter capacitor anywhere around 100 000 microfarad it will hold a charge for a significant amount of time these two terminals up here are hot at this point even though the power supply is unplugged there it is that is unplugged there is voltage charged up in this capacitor i don't believe they've got a bleeder resistor across it i don't remember in the schematic but if you want to make sure that this thing is discharged and doesn't discharge through you do it the old-fashioned way now it's discharged let's talk a little bit about this power supply it's very simple it's a brute force linear power supply it's got one honking power transformer in it that right off your line cord right into the transformer out of the transformer we go through a power rectifier circuit down on the bottom and this big filter capacitor here this circuit board here is the regulator uses an lm723 regulator a very common regulator chip and on the back we've got some series pass transistors also just to handle the current that's going out this is a 35 amp power supply so let's remove the capacitor now that it's safely discharged and see what's going on to remove the capacitor is very simple no soldering iron required we just remove these two screws and we loosen this clamp and there you go this is a hundred thousand microfarad capacitor rated at 25 volts um i've had this power supply like i said powered up for well over 20 years so there's a good chance this thing has failed i looked around the astron website and i found the replacement parts section and lo and behold they have a page just for capacitor c5 that's the filter capacitor for this power supply so i ordered one and here it is now the reason why i chose to go with astron uh to order from them this way i know it'll fit you know you can order these these parts from other places like digikey and places like that you know i didn't want to take any chances i was like you know i'll pay a couple extra bucks but that's what i know it'll fit to install the new capacitor we just reversed the process but one thing we have to absolutely make sure of that we observe the polarity there's the positive lug right there that goes here done i will tell you getting this cover back on is a bit of a project getting everything lined up um that's a bit of a project but you know you don't have to get inside these power supplies all that often it's um it really is in my mind probably the best power supply on the market a linear power supply on the market i mean this thing like i said has lasted me for many years and the guy before me who knows how long he used it for before i got it so this is well over at least 25 year old power supply and this is the first time i've really had a problem with it so yeah capacitor c5 did not repair the power supply actually what it did was um i heard a loud hum and then the power supply died it blew the main eight amp fuse to smithereens so we did some troubleshooting inside the power supply and found a short across the uh the main bridge rectifier and now i suspect that the new capacitor has failed let's just take a look at the capacitor and the rectifier with just a basic dvm and see what we find first test we'll do with the dvm i removed the rectifiers from the power supply to make it a little easier to demonstrate this i tested it while inside the supply but i took it out just to confirm it the red wire is the lead that goes to the main filter capacitor and the transformer secondary gets connected here and here testing your rectifier we'll do is we'll check one direction and we see that it is an open circuit and we go the other way and we do get a reading now we go the other way in the bridge watch this we have a dead short in both directions [Music] so this rectifier has failed i did order another set from astronaut this meter that i have here is is very powerful it can do quite a few other types of tests so i'm going to use this one on both capacitors and again we can look at the state of charging looking at the way this analog display goes i'm going to put the meter into manual mode so it's not auto scaling i have it set to i believe it's a three meg range let's look at the new capacitor first you can see we look at that analog meeting that analog display it's really not moving all that much is it and if i change the scale go down a little lower we're reading about 5k aren't we okay so now if i go across the old the original capacitor that i thought had failed and that same range you watch see where that analog meter went i'm going to move it up a little bit now it's reading one meg but not like the the new one does that same scale we see what it's reading so i think the original the new capacitor has failed i don't know if it came that way or it happened as a result of the rectifier shorting and perhaps causing the capacitor to fail but my guess is that the new capacitor has failed so what i'm going to do now is install the new rectifiers with the old capacitor and let's see what the power supply does if you do this with an astron power supply yourself be very careful the rectifier comes marked with positive and then ac on one side i want you you may be tricked into thinking that when you look at the way these lugs are laid out that oh there's three in one direction and one by itself so when you get the one from astronomy you look and say oh there's one by itself and three facing another direction but you'll notice you might confuse yourself with this looking carefully you'll see that astron when they assemble these this little bridge rectifier they put together here they twist these lugs to make them face the right direction so you can you can set them up this way wire them up this way so be careful when you're looking at the label of the rectifier the new one is marked the same way that's what you want to follow here's the rectifier the new one all wired together um i didn't have any 14 gauge or 12 gauge wire available solid core wire so i had to reuse what they what was in there yeah and it was not easy getting it apart and i'll tell you also it's not easy soldering this all together um you've got to really flow some solder clean up your mess and there's a lot of work to do there anyway i marked the bench with the old one before i took things apart so i would know how to wire things up but kind of how to orient things and get the wiring to the right lengths don't forget the thermal grease on the bottom of the rectifiers we've got the original capacitor reinstalled we've got the rectifiers installed and i'm going to tell you that is a job just if you're gonna do this it is a job even physically installing them back in because you're moving the power supply back and forth and with that honking transformer it's not a not a trivial task but i'm plugged in no smoke let's fire it up see what happens okay it's not humming like it was and we've got we've got output so i'm going to while i have it apart just touch up the metering calibration to make sure it matches what's really coming out of the power supply and um we'll hook it back up and put a load on it see what happens and it's back in its home under the desk powered up i heard a radio fire up let's hit the let's turn the ftdx3000 on and we will hit tune and see what the radio does i'll see what the power supply does quiet as a mouse well looks like the power supply is fixed it wasn't what i originally thought it was which was interesting now i've got the original capacitor back in there and it's quiet so my guess is i probably should have done more troubleshooting before i assumed that it was the filter capacitor you know they say about assuming but i'm glad that we've got everything working it's nice to not hear the power supply anymore and not worry about something blowing up down there so my guess is that maybe one of the diodes in that bridge rectifier had failed and when i changed the capacitor out it did something else caused out of the capacitor to blow it's probably what happened um because it was dead short so my guess is that who knows what could have happened when that when i put everything back together the first time but that said the power supply is up and running i will tell you this is not a project for somebody that's a little faint of heart the voltage levels in the primary of course that's line level but the amount of current that can go through that power supply it can hurt you so that being said if you choose to work on an astron power supply they're linear supplies they're relatively easy to understand um but they can be dangerous to work on so you've got to be extremely careful also make sure you've got a good soldering iron and soldering gun when you've got to do some work and that heavy wiring in there so i hope this helps somebody if you have an astron supply it's in trouble you can fix them and astron's got every part you need for it so so you don't have to worry about that um but again if this is a video that helped you please consider clicking like and also if you enjoy ham radio videos or things like this please consider subscribing as well you know that that always helps all of us youtubers out helps the algorithm of course but it also helps us and i know for me it just gives me a lot of encouragement to keep going with youtube videos when i see likes and subs coming along so until next time 73 from k2 cjb

Channel: K2CJB Radio

Views: 11,501

Keywords: Astron RS-35M power supply, Ham Radio power supply, repairing astron power supply, ham radio, amateur radio

Id: WYaFUBLP4GM

Length: 14min 48sec (888 seconds)

Published: Tue Jul 20 2021