#195

[@rfdave3980]

I have been a Electronics Technician for over 35 years, I would put a jumper wire on the copper foil instead of a blob of solder. But none the less the butcher that worked on it before should get into another line work,. Nice videos Peter I enjoy watching your work. Thank you.

[@EXTIQUE]

RfDave,,i work at a Motorola/Kenwood 2 way dealer. i myself am a bench tech. and I've never seen such a cobbled up mess. it's beyond obvious whoever worked on this radio don't have a clue what there doing. just wonder if they were responsible for lifting/burning the trace(s). or the owner who RP'd the radio did it in. (KD8EFJ)

[@NCMilVet]

What an absolute beautiful job. It is great to watch a master at work.

[@fernandoscrenci4874]

Love to watch that heat flow, when you are soldering!! Peter you plan that perfectly !! Outstanding Fix !!

[@TRXLab]

Thanks

[@KG5IF]

Peter, thank you for the great video and kudos on your methodical troubleshooting of the problem. The owner was lucky to have taken the radio to you.

[@TRXLab]

Thanks Richard, glad that you like my video. 73

[@paultomasetti5164]

Thank you for sticking us right in your way and making that job more difficult for yourself. It’s therapeutic

[@TRXLab]

Thanks for watching Paul

[@philkennedy342]

Nice work Peter just shows you a small error connecting to a power supply can damage a radio at least it wasn’t permanently damaged.. I’ve got a ft817 I use portable brilliant little radio….. I always enjoy watch your repair videos👍👍👍

[@rscelectrical7091]

Excellent job as usual Peter, maybe the previous "repairer" used a gas torch & 6 inch nail to solder with ☺. They certainly made a horrible mess.

[@TRXLab]

LOL yeah must have been a gas torch....Thanks for stepping in

[@vk6op648]

I made the exact same mistake 3-4 years ago. But instead of the simple problem your client had, my ft-817nd blew a transistor on the front panel instead. I tried to fix this but burned a trace and lost an smd capacitor in the process so I relented and sent the radio to be repaired by a professional. Haha. Thanks for the video, really enjoyed the repair.

[@TRXLab]

Yeah sometimes that is the way how it goes.. Thanks for watching 73

[@OrbiterElectronics]

Strange that the previous repairer should miss such an obvious issue in that area. Good repair though my friend 👍

[@TRXLab]

Hi John, thanks for stepping in! Yes agreed it is very strange how the previous shop could have missed it...Hive a good time my friend

[@stevetaylor2955]

Great stuff Peter. Just used your info to do this repair for a friend. Thank you! How did you manage to display "15m FT8" (21:37). Steve G4EDG

[@acestudioscouk-Ace-G0ACE]

Nicely and neatly done as usual Peter. 20W on transmit?!!! The poor little 817 won't live long at that...

[@dinosworkshop6870]

I own an 817. Small and portable. I take it when free on weekends. Great video!

[@webmastercaribou7570]

Always enjoy your work, top notch.

[@MrKelendros]

Good job peter and thx for sharing with us. Really nice seeing those common repairs too

[@TRXLab]

Thanks for watching Carlos

[@ghope10000]

Thanks for the great video. Great job. This error happened to me too. It was caused by an unwanted short circuit at the input of the external power supply. The TCVR was powered up and running on an internal battery. This can happen quite easily in the field. Don't use Crocodile Electric Clips, but use proper connectors 🙂

[@donalfinn4205]

Excellence as usual. So simply explained to me, who knows very little about electronics.👍

[@hancecrawford]

Peter the person who owned the radio was very lucky that there wasn't much more serious damage another success my friend :)

[@masterfranco01]

Nice job Peter, and lucky not much was damaged due to polarity swap. Thanks, greets from Holland.

[@TRXLab]

Thank you Franco and best wishes to Holland

[@PaulHigginbothamSr]

Say Peter on my Chrysler car I am going to try to repair the Bluetooth module so my wife can use her phone in the car. This radio is fairly easy to test by seeing it's reception decibel and or transmit. The module has a standard USB power supply so I will attempt the fix then see if my wife's phone will pair with it for the test while it is removed from the vehicle. I wondered if you had repaired items like this. The problem for me is no schematic is available and will have to noodle it. Thanks for your videos.

[@hamradiotimes5586]

Allsome fix and great video capture. Master at his best

[@VintageTechFan]

Ah, always verify the fault descriptions. Learned that the hard way, too. Especially at work.

[@nasian4641]

Engineers at the design department had probably added the safety 'fuse' just by the large capacitor. Well done.

[@henkvandeleur6872]

Wonderful piece of work. nice that it all went well again.

[@TRXLab]

Thanks Henk

[@Beretta96Dan]

Always enjoy your repairs. I think you sounded surprised that it was back in service so quickly! 73...Dan w4mnc

[@TRXLab]

LOL Yeah Dan that was an easy one..Thanks for watching 73

[@davidj.wilcox6053]

Dip your solder wick in flux first. It will then suck up the solder much more completely. Made all the difference when I first started using solder wick.

[@stargazer7644]

He put flux on the board before he applied the wick.

[@colinp1126]

Excellent video dear friend thank you..it also shows some operators have no respect for their own radio gear

[@TRXLab]

Thank you Colin.

[@chevboy167x8]

Great work and repair! I hate how small all this SMT technology is. I'm not very good at it yet but getting there with more practice and patience!

[@TRXLab]

Yes you already found the right conclusion. With a bit practice you will be in very soon.

[@boxingday11]

Thanks Peter for your time and effort you put in to your videos. Best regards from Carl.G0lka.

[@TRXLab]

Thank you Carl! 73

[@alessandrozax]

A little varistor with a 1n5403 (opposite) diode, can save the owner next time ...thank you to share your experience with us. '73

[@TRXLab]

For sure Alessandro

[@ianharling9569]

Good job as always Peter.At the end of the video I was amazed at how much power was coming out of the little 817.I also noticed the voltage reading on the display was different to the 13.8 volts from your psu so definitely someone has gone into the service menu and god only knows what else has been messed with.😯73.Ian.G7HFS

[@TRXLab]

You are definitely right Ian..We will see when the radio needs new finals...Thanks for watching 73

[@rayfalcone6897]

great video ,Paul,very nice explanation, on what you were looking attend how you trouble shoot, thank you for sharing.......73's N1inv

[@TRXLab]

Thank you Ray! Although it is a honour to call me Paul sorry I'm not :^)

[@nikosalexakis3494]

excellent…… what about adding an diode at the interrupt track to protect from a reverse polarity?

[@TRXLab]

There is a diode but what can a diode do if there is no fuse in the power cord?

[@nikosalexakis3494]

@@TRXLab the diode will prevent the reverse polarity to charge the main capacitor in opposite polarity too and not to destroy any other tracks by sorting .... by all means you need also a fuse at the cord …. and if its not there if the YAESU is wrong or the owner cut it off the cord..... Thank you TRX you are very professional...

[@stargazer7644]

@@nikosalexakis3494 It already has a reverse polarity protection diode in the rig, but it requires a fuse in the cord to prevent damage to the rig. I understand you're asking why not put a forward polarity diode in series, and the reason is because it causes quite a lot of voltage drop which would severely limit how much of the battery you could effectively use before the voltage dropped too low.

[@radionutio81ij79]

That was a joy to watch sir 100% repair thank you for uploading it. 73

[@TRXLab]

glad that you liked it..Thanks for watching 73

[@margaqrt]

Piece of simple advice from a Ham: If you laid down the money for a FT-817, when applying power to it, MAKE SURE the red wire is connected to batt + and black wire to batt - !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! It amazes me sometimes the things we see.

[@TRXLab]

That is the point

[@NullaNulla]

Fuses help too for some funny reason.

[@VintageTechFan]

Red is black and plus is minus!

[@bill-2018]

I wouldn't want to go back to that radio shop if that's the quality of soldering he does. It worried me that I might connect an external battery with reverse polarity on my 817 and h/b radio. I use an FQP47P06 MOSFET for reverse polarity protection. It can't switch on with reverse voltage and there's very little voltage drop across it. Bill, G4GHB.

[@captlarry-3525]

it may "only be a 6 watt radio" but the efficiency of solid state xmtrs is maybe 50% so that's 12 watts or almost an amp and the RX demands almost an amp ( digital circuits are energy hogs) so now you have almost 2 amps going through the solder blob... and in FM mode that is 100% duty cycle.. so a good solid blob is just what you wanted ! as somebody else said, this radio wants a crow bar diode ! and a more careful owner.

[@stargazer7644]

The radio has a crowbar diode, thats what blew the trace. What it needs is a fuse.

[@TheRadioShop]

Good job on the repair Peter. I really hate working after other folks. Never know what you will find. 73

[@TRXLab]

You are right Buddy I hate working on stuff after other folks, too! Thanks for stepping by Have a good Sunday my friend 73

[@JamesP6084]

Hi Peter another intersting video, I remember back in the early CB day a so called Tech had those same lack of skills he damaged more than he repaired :-(

[@TRXLab]

LOL yeah I know him 40+ years ago I was that tech :^)

[@Ordinaryfiveeight]

Excellent work. Professional.

[@madcarew.3256]

Miss connected mine to battery while talking...got away with it on 817 but ruined LDG Auto tuner! Don't talk while setting up!!

[@waynethompson8416]

I own a Yaesu FT-817ND myself and was very interested to see what was inside to cause this problem. When you showed the closeup of the board, I was aghast at what looked like someone had "butchered" the board. The point of the open in the trace appeared, to me, to be where someone had used way too much force with a soldering iron and removed that part of the trace that way...but whatever the cause, it was indeed open. One thing that concerned me a bit was after you cleaned the board, removed extra solder, and then proceeded to power it up, I was worried about several places where under your magnifier it appeared there were tiny balls of solder between a pad and the ground plane. Must not have been though since it worked so well. I am so happy to have found someone else in addition to "Mr. Carlson's Lab" that makes intelligent, thoughtful, and educational videos on electronics. Keep up the excellent work! Do you work on Vacuum Tube equipment as well? I have a love for old equipment that uses vacuum tubes and very much enjoy watching videos on restoring them. Again, keep up the excellent work!

[@TRXLab]

Thanks for kind feed back, very much appreciated.

[@earlrichardet2102]

Another good fix, thanks Peter.

[@TRXLab]

Thank you Earl! 73

[@Gw0wvl]

Great video Peter, But 20 watts output , Its a wonder the final PA isnt ruined at that wattage .

[@وهابالربيعي]

at 5:17 the diode beside the cap. have a bad joint ... it is the protection diode ... it could be damaged too and have a short .... another nice video ... keep the good work

[@TRXLab]

I know what you mean but the diode was fine. Thanks for stepping by 73

[@jfrede1976]

I don't like the solder bridge for the main current path. A little copper wire would be appropriate at this point. But all in all nice video.

[@TRXLab]

Thanks Jörg. In this case I don't see a problem with the bridge.

[@fnordist]

Print abschleifen 1mm Kupferplättchen zuschneiden, mit Zwinge auf den Print klemmen, löten.

[@donalfinn4205]

Jörg Frede Imagine, criticising this genius🧐

[@SoddingaboutSi]

What a bloody mess! Nice recovery Peter.

[@TRXLab]

LOL yeah you are right Simon.. Thanks for stepping in. Have a good time

[@Aleziss]

with that big blob of solder on the ground power input, if the radio is ever plugged back in the wrong polarity, it might blow way more farther since the blob of solder will never break now... I feel it's like replacing a fuse with a nail... also I find that strange that a shop would abandon repair for only a cut trace...

[@TRXLab]

the fuse was missed in the power cord and the trace should not be the fuse hi hi . Well many strange repair shops out there

[@Aleziss]

@@TRXLab ah... that explains the burnt trace !

[@bukucsjozsef9630]

Exactly this foil burned out of my 817after an unatented reverse polarity. If i let me a notes : in transmit, the voltage drop 2100 mV on the pre-filters, inductors including the dc-jack, and a foil traces. This can be observed another 817's.

[@TRXLab]

Thanks for watching but 2.1V seems to be very high..

[@ot7e]

Nice job Peter as always, thanks for sharing. 73

[@TRXLab]

Thanks for watching 73

[@sveinfarstad3897]

Fantastic radio, i love to use it... with the inside battery. :)

[@MrBanzoid]

What a mess!!! I hate working on stuff that other people have had a go on. Missing screws, wrong fuses, even wrong valves (tubes - I'm English!). I even worked on a lighting dimmer pack that had a large area of copper track blown away because a fuse had been bridged with a bit of thick wire.

[@TRXLab]

Yeah 100% agreed hate it too...

[@marksanderson7921]

Good video---please do a video of a 817 with a faulty ribbon cable that attaches from the main unit to the display

[@rjy8960]

4 years on and I wonder if that PA is still alive? Nice work!

[@TRXLab]

yes it is

[@robertcalkjr.8325]

Good job Peter! Thanks.

[@TRXLab]

Thank you Robert 73

[@whirledpeas5644]

Fantastic job!

[@denismatte8727]

good job peter is very interresting good day of you

[@TRXLab]

Thanks Denis 73

[@MC1dash1Bravo]

Awesome video! Enjoyed watching. 73s to you, my friend.

[@mrquick1937]

It appears that may have been a smaller bridge as shown to act as a fuse? I have this radio and love it. Great job!

[@TRXLab]

nope for sure not..Thanks for watching

[@paul-c7541]

Hi Peter, You have to wonder about some repair shops, I have seen in the past a shop repair where they replaced a blown fuse with a strand of wire this was on a customers TV, and given back to the customer like that, however you took this radio and it's working now, I wonder how long it will be, before it comes back for a New set of final's, and to be put back to 5 Watts, some people don't seem to understand this power subject and fascination with more power = further distance, I wonder how much of that 20 watts is coming back down the coax, maybe 15 watts of it. 73's Paul

[@TRXLab]

You are right Paul it is scarring what we see and your example is additional dangerous too...Well the 20Watt will get out as long the SWR is okay but the final stage is not designed for that power...That is one reason why the 817 owner have a blown final club LOL Have a nice Sunday 73

[@NullaNulla]

If you want power from a low power rig wouldn't a boot make much more sense? It would to me at least. Use the several watts as a driver to what ever out you need and buy. Though I don't understand buying low power in the first place if you want power. Luckily I was taught early when I first hit cb by some friendly amateurs who also spoke on cb about wavelengths, swr, antenna matching, antenna types and so much more and it really sunk in fast. However far too many are clueless. I've had great antennas off just stripped coax on magmounts, metal coat hangers etc with good swr. I've only once run a radio without matching (12w) and there were reasons but only for short overs and little use so touch wood never burned a final yet.

[@1natedoggy]

Looks like the previous shop soldered in parts with a Hot Axe.

[@stefanrunkel9013]

19:44 the 334 is short to ground ?

[@theradiodragon2awo]

Weird. I bought one of those recently and after it came , i plugged it in tried to run on BUT THEN I SAW SOMETHING YOU SEE ONLY IN NIGHTMARES + - TERMINALS WERE SWITCHED I was really scared in that moment, so i unplugged it and switched the PSU leads, and FT817ND came to life. I mean wow, in Yaesu they improved it or something

[@111111111Tiger]

Bravo ! Great job !

[@StreuB1]

Another case of "Look what the golden screwdriver has done!" Another great repair!! Peter, do you charge extra when people take it to a chop-shop and then they bring it to you to fix what the chop-shop did? The owner is very lucky, the 817 is a wonderful radio but it can be very expensive to repair!

[@TRXLab]

LOL yeah the golden screw driver... Well Brian we always try to do the best for our fellow hams...Thanks for watching

[@whitney3383]

Good job! ,lucky customer.

[@TRXLab]

Thank you Whitney

[@philippe5394]

Good Job, thanks for sharing this repair.

[@TRXLab]

Thanks for watching

[@bundylovess]

Nice repair peter big thumbs up 👍

[@TRXLab]

Thank you Allan

[@VK2UAL]

I am stunned the owner would have thought that turning up the power on the FT817ND to 20 watts was a good way to go for more power out, power is cheap as his next set of finals. I suspect it was the owner who had more to do with the radio being in the shop than just not putting the right polarity into the rig, no your limitations and it will be a cheaper way to live and it may even give you a longer life hi. Richard vk2ual

[@TRXLab]

LOL yeah that all is possible. Thanks for stepping in 73

[@HBTwoodworking]

I’ve seen you use Flux Off in the past after soldering. What are you using with the cotton swab to clean that mess up? Is it Flux Off, alcohol, or something else. Thank you for making these informative and interesting videos. - Phil

[@BarefootBeekeeper]

Nice work!

[@SomeRandomPerson163]

My first think when I see absolutely 0.000 A current - some trace in radio blowed up

[@andydunham4547]

Good job Peter.I wish people would take better care of there radio equipment. Love your KZbin video's.73 Andy G6OHM.

[@TRXLab]

You are right Andy. Thanks for watching 73

[@stevemercure902]

I see this video was from 3 years ago. Have it been back to your Lab to replace the finals the user burned up after running the radio at 20 watts? Only a matter of time.

[@Spookieham]

What did they solder it with? Blacksmiths tools? What a bloody mess

[@brettvk4bde]

Hey Peter have you ever come across an ft-817 with screen missing digits. Some bright some dull? Great Video

[@rodneythomas8686]

Great job....that microscope makes all the difference...

[@borayurt66]

Hello Peter, That burned out trace looked interesting. I believe it is the main ground line coming from the DC jack, and I expect it to be somewhat thick. Which it is, except for the point where it was burnt which was quite thin and in the shape of a plus (+) sign. That makes me think it was deliberately made that way to act as a fuse (stupid idea to make a PCB trace fuse, I know but that is what it seems). So, IMHO, rather than bridging it with a strong solder blob, it may have been a better idea to use a suitable rated SMD resetable PTC fuse in there? That way, if the owner does the same reverse voltage mistake again, it will be somewhat protected. Best regards from Ankara, Turkey, TA2AWX

[@TRXLab]

Well Bora, if the intention was to use the trace as a fuse we should find this idea in the service manual which we don't. It was rather more the missing fuse in the power cord to protect the radio.. Thanks for comment. 73

[@borayurt66]

@@TRXLab Yes, I know, the idea is rather stupid. Maybe I saw the trace wrong on the video, it seemed like a thinner "+" in the middle of a thicker trace. I was just curious. Thanks for the reply.👍

[@daveys]

Not looking to do it on mine, but wonder how what they did to the innards to get 20W out of it?

[@alfredneumann4692]

I don't understand, that there is no secure diode in the current path. Clean fix! 73

[@TRXLab]

There is a diode but it was not efficient enough or there was no fuse in the power cord... 73

[@iw0hex]

Very nice Peter, thanks for sharing. 73s de IW0HEX Pasquale.

[@TRXLab]

Thank you my friend! 73

[@berniken6511]

Nice job Peter..........................Berni

[@TRXLab]

Thanks Berni!

[@zaperfan]

Another great job done peter. Why do they mess with such small components they don't have the necessary skills to fix.

[@TRXLab]

Yeah you are right that is the question...Thanks for watching

[@kq6up]

My FT-817 is really old. I think I bought it in 2000 or 2001. The display just started flickering and there is a corresponding noise in the RX. The last time this happened I switched the LiPo switch to ON/OFF on the bottom and it seemed to stop (but not sure if that was the actual issue). A couple of days ago, it was doing the same thing on external power. I am thinking since it is intermittent that possibly an old cap is leaking or something similar. Have you come across this?

[@vidasvv]

20W, that might last for a few more seconds lol TNX 4 the video ! 73 N8AUM

[@TRXLab]

fully agreed..we see it very often that radios are cranked up to the max...

[@peterwaine923]

I was just thinking the first guy who got it never even bothered to look at it…lol happens a lot that, they put it to one side, get busy, forget about it until they are my there’d by the owner then just throw it back at them…first attempt would of been the owner, failed then thought sod it, bite the bullet and pay for a professional fix.

[@aureliobelloiz8egm627]

hi what do you use to clean the pcb? tks

[@joshuabaker4691]

Hello I have a similar failure mode on my 817nd. Do you do repairs for customers?

[@OleF112]

Good work on this burn victim, Peter. Sometimes i wish that the companies just put a diode and a microfuse with socket in there. For this QRP radio you can choose small values with tiny space, and were a talking about 3 cents. I don´t like the power jack style..kinda cheap.. But anyways, the radio is now looking good. 73 de Olaf

[@OleF112]

Kleine Ergänzung: Gerade diese billigen DC-Buchsen verführen gerne dazu, mal eben ein altes Kabel von einem Restenetzteil abzuschneiden, um sich einen 12V Anschluss zu basteln. Diese sind nur selten schön SW/w markiert oder deutlich geriffelt auf der +Seite, und dann ist es schnell passiert beim anklemmen....

[@TRXLab]

Yeah it is all about money...Thanks for stepping in 73

[@TRXLab]

Ja das ist sicher ein zusätzliches Problem.. Wirklich blöder Stramanschluss...

[@BruceNitroxpro]

A TINY bit of reverse engineering would do wonders here. I see a couple of excellent suggestions about adding components, and also saw in the video no apparent use of any methods of parts verification either before or after your obvious repair. I would HOPE that ALL the circuitry was given a thorough check for reverse polarity damage... etc. de KQ2E

[@stargazer7644]

He verified the radio transmits and receives properly. The display comes on and the controls work. What more do you want him to reverse engineer and check? The reverse polarity diode obviously did its job to protect the radio.

[@berndb.5097]

.... "I do not have time to fix it" ..... The sentence went on for sure. "..... bring it to Peter" ;-) On the other hand, it is also good that he did not fix it ..... who knows what else would have come out. Sometimes I would really like to know who offers such a service ..... Well done Peter, it would have surprised me if you had not got it healed again :-) 73 Bernd

[@TRXLab]

Thank you Bernd! Yeah it is scarring what you find.73

[@lyntonprescott3412]

Great job👍

[@klausg3614]

I had exactly the same problem, without reversing the polarity and with a fuse in the power cord of my ft-818. No idea, how it happened. I read, it's a typical fault with the ft817. Design Problem?

[@TRXLab]

Yea the design is a bit poor when it comes to reverse power protection...Thanks for watching 73

[@ExtrangHero2023]

How can that be possible that its transmitting at 20 watts. The finals on that radio is only rated less than 10 watts

[@vu3mes]

My 817ND is 15 year's old and has made countless contacts over the years. Recently it looses power output after 45 minutes to 1hour of operations. If I switch off for 5 minutes everything is fine, but once the rig heats up the power output is gone. Is this a heat issue, where should I start to troubleshoot. Any help will be deeply appreciated. Thanks 73 de VU3MES Satyan

[@TRXLab]

yes from the distance it sounds like a heat issue

[@maninthevan53]

yep understand , copper solder brain would be nice too I bet the previous repair shop didn't have a microscope to see SMD circuit , well done .

[@TRXLab]

Yeah most likely... Thanks for comment 73

[@dl7majstefan753]

Peter, good work. It´s always cruel to see, what so called repair shops are doing and that they don´t find such faults, which can be located easily by using Ohm´s law...hi. But one comment: I would have taken a short piece of wire (AgCu) instead of the big solder blob.

[@TRXLab]

Thanks Stefan yeah you are right there are so many so called repair shops outside that so can get scarred...Regarding the solder blob I have never experienced any problem by doing it this way. I agree that you exactly need to know where you can do and where you should do it different. In this case it is a lower power radio and the solder bridge is very short. That means low resistor and almost no voltage drop over the bridge and thus no heat caused by the bridge. Additional to that radio is not installed to a car so no vibrations. In any other case I would have done it as you proposed...73

[@randybehrmann5454]

It looked like the solder at the top of D1085 was cracked. was that something that you noticed?

[@wmanojnishshankadias162]

Thank you very much for make this video. It's really helpful. I always learn new thing from your videos. I'm newbie to ham radio and electronics. 73! 4S6MNJ

[@LeoTV1968]

Sehr interessant Peter. Ich nehme an der Vorgänger hatte vielleicht kein Mikroskop. Das ist aber inzwischen unverzichtbar, wenn man SMD-Bauteile bis 0204 oder sogar noch kleiner löten muss. Und die Augen werden auch nicht besser ;-) Freue mich auf weitere Videos von Dir in 2019 und bleib Gesund!

[@TRXLab]

Hi Leo, ja wharscheinlich hatte er kein Mikroskop und du hast recht ohne die richtige Ausrüstung kann man diese Geräte nicht mehr reparieren..Danke fürs vorbeischauen !

[@pb7379-j2k]

How would just a polarity reversal burn away that trace?

[@stargazer7644]

Most radios have a reverse polarity diode across the power rails so if you put reverse polarity on the rig it will short the power supply and blow the fuse to protect the radio. This radio apparently didn’t have a fuse in the power cord, so the short happened until something else blew. The pcb trace in this case. Without the reverse polarity diode, hooking the power up backwards can destroy everything in the radio.

[@pb7379-j2k]

Star Gazer the question remains. Reversing polarity does not melt traces. Putting 10x the appropriate voltage might

[@stargazer7644]

@@pb7379-j2k Apparently you didn't understand my reply. When you reverse the polarity, the reverse polarity diode shorts the positive and ground power rails together inside the radio. This causes the full current capability of your power supply to flow through the traces of the circuit board. That could be 20 or 30 amps on a power supply, or a hundered amps from a battery. Normally this is rapidly terminated by the supply cord fuse blowing. But if you don't have a fuse in the power lead, then it will be terminated by the weakest track on the PC board blowing open. That's what happened here. See that big diode just to the right of the capacitor at 4:58 ? That shorts the + and - power leads right there by the power jack when you apply reverse polarity.

[@pb7379-j2k]

Star Gazer yeah you’re right, I didn’t understand it. It seems insane

[@stargazer7644]

@@pb7379-j2k This is a simple and quite common method for preventing reverse polarity. You could get away with your serial diode solution on a low powered radio like the 817 if you were never going to run it from a battery. But it becomes rapidly more problematic when your diode has to handle 25 amps on a 100W radio. The diode would be huge, would dissipate a lot of heat and would cause enough voltage drop that you might not be able to get full power out of the radio from 12.6V. So it generally isn't done that way. You can build much fancier reverse polarity circuits using FETs, but the bean counters don't like spending money on things like that. So they just use the reversed diode and a fuse. Just FYI, the overvoltage protection in most power supplies works in a similar way. If the output voltage goes too high (maybe the regulator transistor shorts), an SCR gets triggered to short the + and - output together to either blow the input fuse, or trip the overcurrent circuit to shut down the supply before it destroys your $1500 radio.