Linear Amplifier Killer, silent but deadly
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- เผยแพร่เมื่อ 28 ก.ย. 2024
- One quick but silent and deadly way to kill a linear amplifier is with bad coax. Coax can have a short, an open, be too small to handle the power, but a common and often unrecognized problem is bad soldering on the coax plug. Bad soldering can and will cause the opens and shorts mentioned above which are generally pretty easy to trace, but another common one that is often missed is too much solder on the tip. Yes, too much solder on the tip will make the tip bigger and fit tighter in the SO-239 socket, but that is temporarily. The too wide tip will expand the internal socket connectors out like in a V shape instead of a U shape. I think its easy to see that the V shape will have a lot less contact area than the U shape. Even worse, when you put a correctly soldered PL-259 connector into the now widened V shape socket, you will get very little connectivity if any at all. If your tips have too much solder or are bulging out, unsolder that extra solder, or replace the tip or the whole coax assembly. On the sockets, if it has widened out into that V shape, you can try to reform it using a pick, or replace the socket. It is best to test your coax cables and sockets once in a while before something bad happens. I check for continuity, shorts, loose wires, frays, and loose connections. Kinda like checking the oil of a car, rather be safe than sorry. Here is a link of the followup with the coax and SO-239 connectors repaired. • quick followup video o...
Great video! This has probably happened to so many, and caused continous major damages.
You have a great gift of being able to explain things very well.
Thanks!
I just paused and went and checked my SO239's before watching your complete video, thanks.Videos like yours can save equipment and possibly prevent a huge fire.
Thanks.
Can I say that all of your content is accurate and very good? There are no conflicting agendas, nor do you force an opinion. It's all good information with the intent of helping people, education and showing them things they may never have seen or been aware of before. I know you've helped me, whether it's replying to my questions or putting me on to something good. And I have purchased some of these amps and radios from the States. I have no time for radio snobs, which you certainly are not. Never stop doing what you're doing, that is, giving to the radio community... and I'm a sidebander.
Thanks.
You know, I hadn't ever put that much thought into that extra solder blob...now it makes sense why I have had trouble with a few connectors over the years at times. Thanks.
you can always dress it with a file to get the correct 4mm diameter... but check it with a micrometer or vernier all around so you have it spot on. Check sockets with the blind end of a 4mm drill. After all, a PL-259 is just a screened banana plug.
welcome
Excellent video.
I purchase the best quality jumpers I can find, but now that I see the consequences of a bad solder job that can be present even on a new jumper, I will be checking all of my jumpers just to be sure. Thanks for sharing this information.
I had that problem a couple years ago& my tech said the same thing. He told me what to do over the phone. Needle nose pliers & carefully squeeze them back together. I lucked out & it worked.👍 Nice video.
It's not luck when you do it right.
Hey doc, I'm looking for something between 1500 & 2000. If something comes up I'll give you my 21 I'm in the buckeye.✌️
I tell people this all the time and they still don't get it. Never force a difficult plug in there either. The other thing is, those single split sockets do seem to more often be like this. They come with a lot of American equipment too. The other thing I'd like to point out is the continuity test. I hear people say it tests fine with my multimeter. But as soon as you put real power through it, it's a different story. Especially if it arcs, heats up and expands, or pits. You're going to have an intermittent open circuit, which swings with power levels, particularly on SSB. This I mean for dodgy solder connections, but it applies to mechanical connections too. Always check the plug for discoloration, grey or black.
I agree, especially with the single split sockets. Quad split are much better.
@@tramdr yep, you know your stuff, I totally agree... from literal experience.
Yes Sir and look for white connections. That is oxidation of lead and aluminum. Everyone knows red is rust (iron oxide) but other metals oxidize as well. Oxidation interferes with connections. That's why you have to sand a spot clean for the ground when welding. Think about this, If electricity needs a clean connection for welding (with all of that power and Amps) your radio equipment needs clean connections for it to operate correctly. Ya'll Take Care and be safe, John
Same thing that happened to me. Took 8 pills to the river. Cost me over 500 bucks to get the amp repaired. It's great you made this video.
Sorry to hear that. So many newbies get an amp and kill them quick because of something simple and stupid like this.
There's another connector problem that will kill an amp: cracks in the connector insulator. Inspect them with a strong light and a magnifying glass.
As a retired aviation tech, that cable AND connector are bad news.
There should be four fingers , not a split cup inside the connector.
I use UHF to BNC adapters and quality BNC cables for most of my equipment, and for high power, I like N connectors.
The problem with the UHF connectors is the shell can and will loosen up over time, and cause intermittent connections.
Agreed. Single split is bad news.
It's not over jealous , it's over zealous!
Yes the lump of solder spreads the center of the SO-239 then you have an intermittent connection which kills the final in the amp have seen this dozens of times in my 40+yrs as a tech.
number 27 that has brought that to my attention, thanks.
those are the saddest cheapest chinesium SO239's I ever saw. Well done on the fault finding.
Yeah, those single slotters are pretty poor.
I see this all the time,Doc. Seems they never learn! Thanks and hope this helps many as it is a great tutorial.73 from Goodtime Charlie in da Buckeye
Thanks, Tramdr waving.
The 2nd PL-259 with the "solder blob" which ruined the dielectric core of the SO-239 was certainly a poor soldering job. I recall many years ago from the manual with my 1st soldering gun "Apply only as much solder as necessary to make a good connection" Excess solder may fill up tube sockets, or cause shorts. I have soldered several PL-259 connectors using RG-258 either A or U using just enough solder to make a good connection on the tip. Clip off the excess wire and smooth.
Exactly
Thanks for sharing this with us. I have never thought of this problem..
Happy to help
Yep, if you make up cables and wind up with a blob of solder (like you pictured), Don't heat it up and try to remove it. Heating it to remove it may create a void inside. Just take a file and and file away the excess solder, it will only take a few passes to remove soft solder. I like to use the tiniest amount of dielectric grease on my connections. I just wipe on (and back off) enough to prevent oxidation. I have heard all the debate about 'greasing' coax connections but I have done this since the 1970s with No issues. I'm also saying that you shouldn't even be able to see any grease, just enough to prevent oxidation, no 'Blobs of Grease'.... (I know, I know, your cousin works for XYZ cable company and he says not to...). Do what makes you happy but I have seen equipment acting up and the ends of the cables are white. That is corrosion that will interfere with good conductivity. Nice video and Well done! Ya'll Take Care, John
I agree. At my job we had a machine with undersized connections on a wire harness. Deoxit and other stuff was useless, but dielectric grease actually helped.
I also test SO239s by screwing the collar on the PL259 back and just inserting the center pin. Move it back and forth to see if you feel resistance.
Thats good.
Thanks for the info i have a 2 drivin 8 and thought i had a problem burning up coax and after opening up the box found a burned contact from 1 board to the other both have pills but incomplete circut not sure what happened
We understand what you are saying and about how a SO239 IS SUPOSED TO WORK.
Thanks.
The problem is that the heat causes the Teflon insulation to move and allows the connector to expand. Replace them with genuine Amphenol phenolic connectors.
can't beat Amphenol
My local friend borrowed my RigExpert AA-170 and he could not get the plugg out again and rift the whole SO-239 plug of my swr meter cause he had so much soldering on the PL-259 he forced in so it get stuck inside just as we see on the movie here ( Nice movie you made here so we can pass it on so more people understand not to oversolder the plugs
I fixed the SWR meter but got pissed when I saw the soldered plug who was stucked inside SO-239 lol 73 LB7VI
When I was a kid, I did that myself a few times.
You can't get this problem with an N Connector! On the occasions I have to make off PL259's, I have ALWAYS used a utility knife to carefully shave off any excess solder remaining on the pin . It will cut off like cheese in thin layers. Nowadays for high power I usually prefer to use the PL259's that have a braid clamp just like an "N", rather than rely on the poor design of the standard 259. But sadly can't seem to get these types from anywhere except China... :(
I agree with the shaving and have shaved a few myself.
Hey buddy !! Thanks for doing this vid . Andy UK..👍🏾
Any time!
Holy Shit !! I haven't heard the term mud duck since the '70's......my man is OLD SCHOOL knowledged up....and also the FIRST American I have ever heard actually pronounce the L in solder.....
LOL I've been into this since I was about ten, so 50 years now.
Great tip! Having made my own patch cords, I can put that information to good use immediately.
Glad it was helpful!
It’s not Amphenol SO-239’s on the meter. There inferior nylon plastic insulators never work well at high rf levels. I prefer ceramic or polyurethane with a 4 finger port inlet that will contour and spring to that larger blob of solder on the center pin. The one slit tube inlet is a poor design. And for the blob even if it was pro made…it would take a brief hit with and iron or very least in a pinch scrape it with a razor or knife. Very careful inspection 🧐 and great explanation!
agreed.
It is easy to make good jumper cables, once you learn how. I made some bad ones too, when I first started making them, I had to rebuild several.
Yes, there is a learning curve. It was like 50 years ago for me lol.
All it takes is one catwhisker from the shield braid to drive you crazy.
I know it's not convenient or good for servicing, but wouldn't soldering in the coax directly eliminate a lot of problems. Making jumpers solid connections at both ends.
Yes, but most of us change around stuff too often. Another similar problem is with 3-500z tubes. A 500z pulls 15 amps a piece plus the heat from the tube kills the pin connection. When I was a kid and I rode with an older bud to Blackcat and they soldered in directly his JB-2000 3-500z tubes to the sockets. I thought that was crazy, but then found out when you had a bad tube, you would replace both the tube and the socket together anyway. Last, Browning Mark 4's have a connector problem too and some soldered the cable directly.
"Over Jealous?" Was that person worried the jumper cable was going to cheat on him?
You are number 26 that has brought that to my attention. Thanks.
Thanks for the warning!
Any time!
The solder was probably put on because the holes were already too wide , and they were trying to get a better connection
When I was a kid and still learning, I would have done that too.
Thanks it's the small things i could care less about that makes all the difference.
Most the time, it is something small and stupid that messes everything up.
Over jealous or over zealous?
You are number 25 who has told me that and counting .
Great catch. Thanks for the video.
Thanks for watching!
yup you right never really though about that , but that could be fix with a thin screw driver or a thin object and close the gap a bit. maybe it might help to keep it clean, oxidation is a bitch, tuners with a roller inductor get oxidized and the swr will jump also . thank you
This is a darn good video !!!!
Sorry for bad thinking on 5:00 and even more on 6:17 😆😆😆
LOL shame on you!
I've laid a couple of silent but deadly farts in the shack. Amp still hums along.
Keep trying, you will get there.
All PL-Connectors need contact griese, or they burn black out, then crashes the Final.. The loosing is not the problem, the capacity is then a part of antenna, but if it move util powering , an crash stay befor.
I never used or tried grease.
4:01 the most erotic portion of this technical briefing.
I just had that happen. But it didn t ruin the amp. I took my pocket knife and carve off he extra solder. I made it hard to plug in I didn like that.
Yep.
I had some of those jumpers I got off ebay 10 years ago. they sucked because I could see birdsnests in the braid. the connectors were ok but thats it. these look like the same crap clear jacket
Bad coax is a big time amp killer.
Very valuable video Doc, also the bleeder resistors video very valuable information for the new bees! JohnBoyUtah KJ7TBR 🇺🇸😎📡🎙
Thank you kindly
You should buy a LiteVNA or a NanoVNA! :-)
Wouldn't believe how many so239s I had to replace because the extra solder spread the inside of the so239
Yes, I would.
"Over jealous"? I believe you mean over zealous.
Well, I'm old and do these vids late at night lol.
Great Video! 73 DE W8LV BILL
Thanks for the visit
"OverZealous", NOT "overjealous".
Thanks, you are number 22 that mentioned that.
Like throwing a sausage up a hallway now 😞
ummmmm, ok.
Artificial diode (poor solder joint plus corrosion) time...
Yep, connectors and relays are a major source of problems in amplifiers. Old corroded dirty and loose connections because of dirt corrosion time.
More solder , more better
sometimes less is better, like with drive too.
Good info! Something to watch out for. K5UDO
Thanks for watching!
😂 well cheep So -239’s and A Junk Jumper and we’ll the wrong length!!
And by the way, what is over jealous ??? I think the word you were looking for was over zealous?
But realistically, the jumper length should be a half wave length electrically no matter what coax you use that’s what you really need to feed a unit not 1/8 of a wave.. not beating on your video… just trying to help a little bit
Whats funny is that a mostly agree with you on coax length except I think a half wave is best, but quarter or 1/8 wave might not be as effective, but do you really run a half wave from radio to driver, then from driver to big amp and then from big amp to wattmeter? I had this discussion in a Facebook amp group and you should have heard all the mud ducks trying to tell me how wrong I was. Also, you are number 32 that has mentioned over jealous to me.
@@tramdr
Yes, 1/2 wave electrically from the radio to the driver a lot of the bigger units like to see 1/4 wave of coax between the boxes shows how the HG seem to work out some of the older Toshiba‘s kind to do the same thing … depending on the HFE of a transistor will affect the coax sometimes or how the amplifier is tune but if you watch my videos on Facebook, I clearly talk about VOP and every video is very very important to the equipment that we build kind of like breaking your shoelace, can you still tie a bow in your shoe?
Anyway, you cut it very rarely a eighth of a wave coax or a 3 foot piece is typically always wrong if you actually take and look up the Coax that is that mini eight or the foam or the truck driver stuff the VOP is 84% so they don’t even come into the proper equation But if you know this people normally don’t talk about it but if you don’t know what they always talk about it acting like they do know about it if you can follow all of that…
Anyhow, good luck good job try to educate. The general public is very difficult. It’s a big hill to climb.
@@tramdr
Yes always run a 1/2 wave fro the radio to input of the driver then depends on the big box the phase angle can Chang ! You may need to change to an 1/4 wave to match the input of the big box and the output of the driver… the only way you can make sure is to do a test with a bird!
Yeah, this problem is super annoying. Sometimes you cannot even tell that a connection went bad somewhere after some kind of storm.
Thats why SWR meters are important. Commercial Bird Wattcher wattmeters had a circuit that automatically unkeyed the amp when SWR passed a certain point.
Good fault finding but TOO LONG AND REPEATING THE SAME THING.
Thanks, I'll keep that in mind, commit that to my memory bank, make them short and sweet, small but powerful, condensed not expanded......
r/BoneAppleTea .... Overzealous not over jealous :)
Thanks, you are the 23rd person and counting.
Great example, informative. I think you wanted to say Overzealous soldering, not over-jealous 🧐🙂
Thanks, you are number 28 who has told me that.
Overzealous not overjealous LOL but I like overjealous better.....They must have been overjealous of the pros soldering skillz so they said F it ima hit it with the GLOB!!!! A+ vid. straight to the point... good stuff! subscribed
Thanks, you are number 36 that told me about that.
Good point and worth checking your cables and sockets
Thanks and agreed.
hi buddy.. i cant believe you have had to make a video of other peoples utter stupidity.. this is class one knowledge of how not to connect a plug for a jumper lol.. stay blessed
More like this coming, you won't believe some of the other stuff I have seen too.
@@tramdr umm this should get very interesting lol
At 3:34 , did you say "over jealous" ? Do you mean to say over zealous? There's no such saying as over jealous.
Thanks, number 29
That happens alot. Great video. Ironman in Alabama 73s
Agreed.
Most of us have a multimeter, and it will tell us most of the story. Electricians have a stronger tool, one that checks the strength of the insulation. It's commonly called a "megger", and it will reveal problems that a multimeter cannot.
Amplifiers can produce voltages and currents high enough to reveal problems that don't exist at lower power levels.
If you have a situation where the SWR is good when barefoot but goes south when the amplifier is on then you've got an insulation problem.
Meggers are cool, but how many people have one of those?
@@tramdr That's true, unless you're a commercial electrician you probably don't have a need for one. We had them at the power station and when I was a contractor. Now that I'm retired, the odds of my having to test 4160 volt motors is nil to none. Those were the days...
@@tramdr They're so used to test transformers.
There's some Cheapo Meggers available nowadays. 73 DE W8LV BILL
Excellent..Many thanks..I’m 78 years old, and I’ve just realised I’m still learning! Thank you.
I don’t understand why people use those shielded banana plugs at all. SO-239/PL-259 is just trouble and not made for RF. I change everything to N connectors if it’s delivered with SO-239.
Sure N's are a lot better, but its a real PITA to go all N, pun intended.
This is good info especially when you’re buying used equipment.
Gotta admit that I blushed when you did the visual. 😂
I thought bad on exactly time I saw 😆😆😆
I blushed when making it LOL
Magnificent information
Glad it was helpful!
Now I have to check every cable I own. Thanks for the warning. 73 to you!
Glad to help
ran into that a lot ..
me too
I always take a razor blade/knife to the end of my connectors to remove any extra solder and make it as smooth as a babies butt.
Good idea.
And if your amp has those awful HEP transistors, they all pop immediately. I wish they still made the TRW transistors. I have accidentally keyed them without any load for 10 seconds without hurting them. I’m 66 years old, so I’ve seen a few things since I started electronics when I was 9 years old.
A tip for beginners too, if you take an RF power transistor out of your linear and test it, it may test fine. But remember that inside there are many transistors in parallel. You could be testing only one good one and the rest could be open. The only thing you can really do is try another one and see if the power output is okay. That messed me up when I worked on my first transistor linear. And keep in mind that Turner made a bunch of +2 microphones that had transistors that tested fine on an ohm meter, but they had no gain! That one really stumped my electronics professor at the university!🤣 73!
I'm a tube man, so I'll leave the transistors to you.
I use BNC cables exclusively. They're good for a lot more power than people think. They're more reliable, more convenient, come in water tight varieties, and are an actual standard RF match.
I like BNC's but would not use them for high power though.
I like them for fast connection and for some HTs and Portables, but I find they have more play/wiggle room at the connection, so I don't trust them as much.
Yep people dont think about this stuff.u have to make sure ur solder on the tip is not greater than the pin diameter.solderwick the pin tip if your sloppy.use a file worst case to file off the extra lead.also clean and inspect your so-239 for good friction on plug in.i use deoxit and q tips to clean out the black oxide inside the so-239.rf hates anything thats not clean and very conductive due to skin effect.oxides and flux films as well.thanks for video.god bless.766 pa.
I use a small soft brass brush on the insides.
@@tramdr good idea.
Thanks Brother. That’s something to really watch out for.
You're welcome.
Great video! Very informative! I need to check my patch cables now. Just one thing, it's over-zealous, not over-jealous.
Thanks, you are number 36 who has brought that to my attention.
Holy Moley.
My × Old lady's.
LOL
😂😂😂 like a woman who's been with to many men lol
Allllrightie then.
* Over-zealous. 🙂 Over-jealous is a whole different topic.
Thanks, you're number 28
PL259s come in 2 types. Those with a white nylon insulator should be avoided as the insulator goes soft and distorts when heat is applied and fit badly after cooling. Look for examples with a brown bakalite look insulator which don't have this problem.
Ian G4JIU
True but bakalite isn't used much anymore.
You know, i got a jumper laying around that never seemed to work quite right you get high swr with it inline or sometimes great swr or sometimes the power just reads low. Now im gonna go and look if its messed up on one end and if it is really look and be sure it didnt mess up the jack on my meter
Just throw that one away.
PL259 are RF connectors, yes I suppose you can use them for audio......but I wouldn't.
I wouldn't bother either, but they would be better than RCA connectors for audio.
Yeah, a bad solder joint, but I'm a fan of copper coax too, hot and ground. A little emery cloth wouldn't hurt. Just a minute or two.
Yep.
Just a thought, surely run the patch lead with protective rubber grommet to protect the coax straight to the board. No more problem leads
That surely would help, but its not a fix all.
whats with electricians and those old yellow mulitimitters? ur the fifth guy I saw with one of those 3 in real life 2 on the internet
Fluke is the real deal, sir. Kinda like a Bird wattmeter. Except no substitutes.
They was a bad connection problem with my x wife. I think diagnosis Peter bombed!
Sorry to hear that.
Fer ceissakes, get a DMM with a more civilized continuity sound, will ya?
Which one do you suggest?
Explanation at 6:00 in a nutshell... A big pin ruins a small socket :D
If it don't fit, you must acquit.
the old fluke has been around the block a few times lol
That's what Fluke's do
This principle of "Wetting the joint" applies to any soLder joint. If both parts are not wetted correctly, you will get a bad joint.
Note the "L" in soLder, it's not soder!
good soldering is an art. There is a lot to it.
@@tramdr Yes it is, but understanding the principles and being able to identify a good joint against a bad joint and what's wrong with it is key.
Tripod, he said! My kingdom for a tripod!
ok
easily spotted before testing, an im gone.
As most things are, easy to see if you know where to look and what to look for.
Over zealous, not over jealous.🙄
ok, thanks, you are number 19 who has told me that.
EXCELLENT video Sir.
So nice of you
Very, very useful that will help many CB and Ham Operators!
I hope so!
You are so right
Thanks.
Lol......continuity checks dont apply to rf!!! The jumpers were prolly ok with low power and looking fine on DC but rf sure wants to "jump" out of conductors!!!! There was no fault from the amp there. Lofl.....and it's always the mud ducks who are out of tune that tell me that it's my rig that's out of tune.....I guess all my ham rigs are not near as good as their ancient mobile cb radio......😳😳
ok
......the next day I checked all the inputs and tranceiver outputs, all needing abit a tweaking and cleaning.I have 1 new chasi mount so239 that I might put on input to TX800 the output is replaced &new thinking all is good, but not so after this video.After the maintinance I see less reflect & abit lower standing wave.Thank you very very much.
Nice work!
I am not a fan of PL259 connectors. I prefer a crimp or right angle version as there is no risk of getting excess solder on the connecting surface of the pin.
I had some cheap Right angle adapters. They failed so much, I threw them away.
Ive run into that samething on some of the used amps l have bought.Nice touch porno hands.😜
LOL
The blob strikes again . Well done !
Good one!
Good diagnoses, and good observation.
I'm not in the same field, but must deal with male/female connectors often, where moisture is at times present, and many times 5 volts dc. Molex connectors and their much, much smaller cousins, I don't know what those are called.
A good percentage of issues/ failures that result in a repair with a particular component being blamed are in fact misdiagnosed. And it usually occurs with 12 vdc or less, with one or more of these tiny connectors in series with the component and the source. What I call 'micro-corrosion' is another invisible killer. It's very easy to interfere with 5 vdc, with extremely low milliamps, or even alter it, with nothing more than a poor connection. Quite often, disconnecting and reconnecting will at least temporarily alleviate the malfunction. (Around the shop I call this ' dry-fuxking' the connection, ahaha) 12 volt dc components very often are perfectly sound, but the power supply is being interfered with at the connector. What I wind up doing is scratching both sides of the plug and deforming both sides enough to insure a very good contact. Or just hard wiring and eliminating the problem once and for all.
At my job, I worked on a machine that ran a data ribbon cable from the power supply in the chassis to the computer board +5v and the +20v lights on the lighted front door. This ribbon cable used one lead for ground, one for +5 and one for the +20. You could actually measure the voltage drop not only from the connector, but it was dropping some voltage thru the small wires of the cable itself. You could have +5 at the power supply, but would loose about .3 volts at the cpu board. Of course the CPU board did not run good like this, lots of problems with that machine. Company fix was to keep replacing the ribbon cable. Field trick was to use anti oxidation compound which did help some. The ground was isolated from the chassis and on some, I would run a ground wire from chassis ground to cpu ground and for the +5, I would run a normal wire from the power supply to the cpu. That worked great, but the powers that be decided they wanted all the machines to be uniform so they did not want me modifiying their machine anymore even though it worked great with my mod.
@@tramdr haha! Management. They are usually only there for looks.
I make an effort to keep them out of the loop as much as possible. If they start asking questions I either play dumb, or give as little information as possible. Staying under the radar allows me to increase production while not working so hard. And what would management know about that?
It's amusing how the people with little or zero actual skills will attempt to become some form of low level 'assistant manager' and get some company cards made with their name on it. Little do they know they are merely the managers assistant.
Even more predictable is how a manager will always chose a person less intelligent than themselves, for obvious reasons.
Mismanagement in America alone costs the economy millions and millions in revenue, I doubt we are alone. But it does create a nice level of job security for the more skilled and savvy.😁
Hey bro, I drove tractor -trailer for many years and had radios inside and I have never had a coaxial nor a jumper to a linear that loose. Just like heat is a killer to electronics, well an arc is even worse, I am not sure if any kind of surge protector could have helped against that...just the same, if your swr's are to high it doesn't matter if you had a loose connection or not, it will blow your pills (transistors), I ran an 8 pound maul off and on for several years and didn't have a problem, crystal clear with any radio I ran, I kept a meter to check my swr's and would never crank the power up until I seen at least 1.5 or less.
You can't just open an antenna and mount it hook up and blow smoke without issues.
Aw yeah and another thing also, sometimes a person may not have their antenna ground well and the swr's will fluctuate, and another thing also, that little plastic piece inside of the coaxial junction that will be considered part of the mounting bracket I guess you would call it, if it isn't in good shape it can also cause issues.
Yep, bad insulation, bad ground, bad jumper, bad SO-239, dirty connectors, frayed wires, loose nuts lol, undersized coax, and more. I once sold a guy a 3kw base amp and he brought it back 2 days later blew up, along with his blown up SO-239 off his beam. Of course he told me that is not what caused the amp to blow up though.