JBL MPX600 Amplifier Repair : Can A Blown Channel Have A Short If The Fuses Are OK?

[@TheEmbeddedHobbyist]

Dust and dirt have two properties depending where they are. if on two conducting surfaces they insulate, between two different potentials they conduct.

[@andymouse]

They can, when found in micro fractures even form semiconductors and can measure as diode junction.

[@TheEmbeddedHobbyist]

@andymouse well when you look back at the cats whisker diode in old crystal radios it not too surprising.

[@andymouse]

@@TheEmbeddedHobbyist :)

[@Dutch-linux]

@ timestamp 11:00 when it goes in protect en the signal and clip led's are on that means DC on the output why it stays in protect

[@thulinp]

54:58 that's a classic cracked solder joint, below the webcam. But the pad doesn't go anywhere, so it's fine. Edit: This goes to R631, so it's a problem.

[@Dutch_off_grid_homesteading]

Heya, love this way of trouble shooting the unterstanding of these circuits goes faster and faster for me. @1:16:03 you measure R635 and R646 and they were ok but it looks like that there is a crack in the grey part maybe they are still stressed even wen they are ok ?

[@chadmartin479]

good job thanks

[@LearnElectronicsRepair]

cheers

[@LarixusSnydes]

1:03:16 R635 and R646 look cracked in the middle and to the left respectively. Very interesting repair video btw. Thanks :-).

[@LearnElectronicsRepair]

nice to see you enjoyed it

[@ISquishWorms]

Enjoyed this one, will you be showing us the repair once the parts arrive?

[@LearnElectronicsRepair]

Yes for sure. The customer managed to get the 2SA/2SC transistors at the electronics shop in the capital Las Palmas (he got me five of each) but he couldn't get the MOSFETs - well he could but only the SMD package not TO220. I already have the resistors. So I've ordered the Mosfets hopefully they won't take too long

[@2009numan]

should have used an impact driver to get the screws out

[@sivoltage]

From experience an impact driver would destroy the screw. I fine HSS drill bit its generally the only option.

[@SkippiiKai]

​@@sivoltageI hope he means a an impact screwdriver, which is the correct tool for the job. It's a screwdriver with a mechanical spring loaded thing that rotates the head as you tap the back with a hammer. Works like the rotating thing in a retractable pen clicker, and it's never let me down removing rusted phillips screws. Because of the design, the rotating torque is applied as the driver is pushed hard into the screw, preventing stripping. I don't *think* @2009numan is suggesting a pneumatic ugga dugga tool for electronic repairs.

[@andybutt5609]

You would need a solid base to hammer against for an impact driver. Not sure it would work in this case

[@LearnElectronicsRepair]

Probably I should buy one of those. It's the first time I came across this problem in recent years but like buses you wait ages for one then two usually come at one

[@LarixusSnydes]

@@SkippiiKai Thank you, now I know that these tools actually exist that could have easily saved myself two days of work while replacing a degraded balcony at my girlfriend's home. I have read the reviews and have come to the conclusion that on these tools you should definitely not skimp on the price, including the bits. I'll buy myself a properly made set.

[@darylmcgee4349]

Looking Forward to the next instalment of this one. So much is wrong

[@OnStageLighting]

Me: Open up, see state of everything, nope-ing it right back to the customer LOL. But being serious, I just don't take stuff of this age - it's always in complete state that doesn't deal with disassembly well and likely is not gonna the hoped-for 'loose wire' that the owner assumed.

[@LearnElectronicsRepair]

I think a lot of equipment here is of this age to be honest. So I guess you work on it wait in the hope of someting newer to urn up. This stuff sounds amazing when working by the way

[@stevejagger8602]

Should ceramic body resistors be mounted away from the pcb on ceramic beads to avoid heat damage?

[@LearnElectronicsRepair]

That would help. I guess it depends on how hot the designer expects them to run in normal use

[@stevejagger8602]

@LearnElectronicsRepair I think the same reasoning applied to MOVs which are sometimes found shrouded in heatshrink sleeving to protect surrounding components from results of that final over voltage!

[@tonypacke6954]

As with some of your computer purchases, all seem to be very corroded. Is this because of a high humidity problem or are these things used on the beach and are late to be brought in when the tide arrives?

[@LearnElectronicsRepair]

Yeah we have that problem on the Canary Islands. It hardly ever rains (well not in the south of the island) but we get regular Calima which are hot and dusty coming from the nearby Sahara, and you cant get more than about 12 miles / 20Km away from the ocean anywhere on the island

[@freedog632]

What is that schematic website?

[@LearnElectronicsRepair]

elektrotanya.com/ whoever she is

[@davidhollfelder9940]

Protect mode with signal indicator lit .. Deja Vu from the powered speaker job.

[@pwal8468]

For a little more, I would buy from Digikey and get them in 2 or 3 days...

[@2009numan]

that amp looked well looked after LOL plenty of rust on it

[@izzzzzz6]

Down by the sea! The owner would do well to recondition the lid while it's off. I find stone chip spray paint for cars can do a nice job.

[@harrygood4783]

The amount of dust would not of helped with cooling of the internal heat generated by the transformer & circuit components, I was building such amplifiers in the late 70`s & 80`s, the use of large components was standard practice, there really should be a blow in fan and a blow out fan to give good air flow ventilation, thats why the amount of dust is present it`s blow in only, it`s bad design, that why the component level is so high. On the subject of secondhand over new unbranded models might have a difference over the bias setting, but all this does is reduce the clipping so you don`t overdrive the speaker frequency tolerence and damage it, looking for the lowest voltage and or use a scope but i guess you know this!

[@NotMe-cx3qv]

The"new" fqa36p18's I got just measure as diodes , so fake they aren't even fets . The "pulls" in that flavor seem to function

[@gordthor5351]

It looks like one of the emitter resistors is broken.

[@Karthor.]

24:12 - isn't those test to learn AI? could be wrong but that's what i've heard but yeah i don't like those test too

[@dons8365]

Can A Blown Channel Have A Short If The Fuses Are OK? Sure it can if the short to ground is less in amperes than the fuse controlling the circuit.

[@LearnElectronicsRepair]

There is that, though it was not the case in this instance, but the video title obviosuly did it's job regardless 😅

[@Irilia_neko]

On resistor is probably definitive, the ceramic is broken

[@Irilia_neko]

You find it way later, I saw it at the start of the video 👀

[@Irilia_neko]

This is definitely from a recycling center 👀