How to repair Sony STR K840P in protect mode!

Here I trace out the reason for this unit being in protect mode and with parts becoming harder to get for older models I find an alternate solution!
Tools I use -
Soldering
Quick 861DW hot air station
Duratech TS-1640 solder iron
Multimeter
RMM760D - can be found under many name badges
Microscope
Luzky Zoom 3.5 - 90x simul-focus single boom stand trinocular stereo microscope
Camera - Lucky Zoom HD 14MP
Oscilloscopes
Siglent SDS 1102CML 100MHz 2CH
Philips PM 3305 35MHz 2CH
Bench supply
Powertech MP-3086 0-30V 3A
TL866II PLUS universal EEPROM programmer

[@Jaenu128]

Thanks very much for your comment on resetting the receiver, saved my day (and receiver)!

[@maxwang2537]

That's great. I have not seen an IC module being repaired before as well. Well done mate.

[@JonnyFix]

Thank you. Glad you enjoyed!

[@MrSilv55]

@@JonnyFix Thanks for the video , i have an old Sony receiver str k850 that won't memorize preset radio stations no more, i have to manually put in frequency in order to tune in station ,but if i try to set up another frequency it looses the first one and so on, this might be old caps, what you guys experts on radios think i should look for, thanks

[@AnonymousRepair]

great repair 👍

[@hardkore360]

thanks for the video!! I have a Sony STR-DN1040 that was giving me that same protection mode display error, time to get it out of the closet and find some schematics!

[@JonnyFix]

Good luck. Hope you have fun trying!

[@klausschreyer7062]

Good Find Mate. Genius My Sony Receiver doing same thing disconnected all back leads tried to Reboot few times still got Protect Display. I'm going to Replace Module STK 350-230 and Hopefully takes care of Problem. I don't see anything else Smoked. Cheers 🍻 Thanks for your Time and Effort to make this Trouble Shooting Video

[@AlanLiefting]

Giday! I am also a tech here in NZ. Good skills with the repair. I have never pulled those hybrid units apart to repair them. BTW, the STK350-230 is available as a spare part.

[@JonnyFix]

Thanks. I didn't try local agents but saw I could get them from China. Nothing to lose given the transit time!

[@jykozak]

My air conditioner died right before we left for a week of vacation here in Texas (think 100+ F heat). I was able to fix my AC but then noticed my STR-K840P was apparently dead with "PROTECT" displayed. I thought it was maybe the week of high heat exposure that did it but maybe that's just a coincidence since the receiver was not used during that week. A little Google'ing found this video and I noticed the date you published it. Happy coincidence! Unfortunately, I have ZERO experience with electronics and a few minutes in made it clear that this repair is way over my head. If you want an extra receiver, let me know! :D

[@JonnyFix]

It may be the same fault, it may be something else. If it's the same the module I repaired could be removed and the unit will work just with no center channel which may not matter to you. I guess you could remove it just to see if it works again. If you don't have the tools to unsolder the pins to it you could, if you don't care, destructively remove it like say cutting the pins. If you can't get cutters under it I'm sure enough back and forward flexing would snap them eventually. Don't let the remaining pins touch each other. Just a thought :)

[@roblet5047]

Hi bud, did you ever get your Sony receiver repaired, I would be happy to buy it off you to try and fix. I repair Pcs, laptops, Mobile phones etc. My amp went into protection so now trying to learn about this stuff now lol. If your amp for sale let me know.

[@zx8401ztv]

Well done :-D When you showed the drive coming from a deadly stk i thought Oh shit! lol. I wonder if the words " The modules dead, i cant make it any worse. " came to mind :-D And you won :-D, thats brilliant. I've had amplifiers stuck in protection, but it's always been the outputs and a fair few passives dotted around them. Special diodes that are unobtainum and substitution using a data sheet to see what i can get away with. I know you have been there lol.

[@JonnyFix]

Yeah it's no harder than working on an iPhone really so give it a go!

[@blogdeldia]

My K740p works OK except for the front speakers. Surround, center and subwoofer are fine. You mentioned something regarding voltage on the output terminals, I wonder how to troubleshoot this to make sure that part is burned or how to troubleshoot it?

[@JonnyFix]

I would think you would have a fault indication if there was voltage on the front speakers and nothing would work. I would start by checking the solder joints on the relays for the front especially and over the board in general. A bad connection is most likely cause. If the relay isn't on because of voltage out of the amp section you would be able to measure this on the relay pins. Try and find a schematic/service manual as this will help finding which relay and which amp section to focus on.

[@blogdeldia]

@@JonnyFix i tried, but my multimeter is broken 😔 I opened the unit and I was doing a test feeding CD source with my phone, no sound. I was going to let it rest for today and pushed the tuner button by mistake. Front speakers worked, so it is not contact related. Where should I look now? 🤔

[@blogdeldia]

@@JonnyFix I've found the manual, it's here: www.dropbox.com/s/qonrx12t2tcfa0v/STR-K740P_K840P_v1.0_.pdf?dl=0 From what I've just found the FM card sends signal to front speakers, but the other cards (rest of inputs and digital inputs) don't. They do send to rear and center speakers though, where I infer it has to be something in the main board. Can you take a look to the PDF and tell me what should I check please? I can get a multimeter tomorrow. (My electronics knowledge it's close to zero) 🙈

[@maxwang2537]

You "gently removed the plastic cover" ... Magic happened! how did you remove that?

[@paoloevo9]

great repair!! i have the same problem on str-de595. i have removed the stk350 and the amplifer turn on and no protect.. i have open the stk.. the diode it's zener diode 5.1v?or normal diode??? thanks from italy! bravo!

[@JonnyFix]

It is a normal diode which must be rated to >50 volts as per the rail that feeds it. Good luck!

[@paoloevo9]

@@JonnyFix thanks..i have tried to replace the diode .i used a 1n4148 smd,but showing protect.. stk its died..i order a new 1..ciao

[@JonnyFix]

@@paoloevo9 Did you test the old diode first? This isn't a guarantee the same part will fail in all. Test the other ones in there just in case.

[@paoloevo9]

@@JonnyFix yes..i tested the diode..drop voltage 1.2v! not correct.. not 0.6/0.7v.. yesterday i replace the stk.. the amplifier it's ok.. the repair inside at the stk it's an experiment..ciao

[@paoloevo9]

i am a professional repair from italy..complinents for your channel!!

[@blingfox]

I have the same model. But my Problem is that the sound goes off sometimes. And when you press on the back where speaker lines goes in. Then the speaker work again. Have checked the solder point and re did them but still same Problem. Even cleaned the holes from wire scrap.

[@JonnyFix]

You may need to look at the main board for bad solder joints. Flexing the chassis may also be flexing the board where these usually develop.

[@blingfox]

@@JonnyFix thanks ill take a look. I thought the same thing

[@ernanfer2]

Hi, i've a sony stk-740p and it show "sp.off" in red. How I to fix it? Thank

[@guinamax4390]

Bom dia Fernando, tenho o mesmo aparelho com o mesmo problema, vc conseguiu alguma solução?

[@ernanfer2]

@@guinamax4390 no ...al paracer es pronlema del ic central que hace eso

[@2121e4145415151666]

@@ernanfer2 did you fix the probleme now ? cheers

[@fabrodino]

Tengo ese mismo problema si lo solucionaron respondan por aqui

[@fabrodino]

Muchas gracias

[@mediilbrahim2835]

Hi there I need your help i'm ordering xgecu tl866ii plus I need to know how install the software if you could send to me a file

[@JonnyFix]

I believe all the info you need is on their website

[@mediilbrahim2835]

@@JonnyFix thanks for reaction, , I couldn't find any thing that help ,, should I plug the prog first to the PC then I download the software?

[@JonnyFix]

@@mediilbrahim2835 It is on their website. If you have a knock off copy instead of a genuine device then you're on your own.

[@dipakbhalodia7155]

Service manuals how to download side links provided me please

[@JonnyFix]

Search Google it's easy

[@v8snail]

NO USER-SERVICEABLE ITEMS INSIDE...My arse there isn't.

[@JonnyFix]

Hold my beer...