Master Audio P318A Tri-Amp Class D +Active Class AB Speaker Repair

[@mayeraus41]

I think with the MOSFETs, the gates may not be grounded when the circuit is off and they may have collected a charge, which might be causing them to read like a resistor and not an open circuit.

[@Dutch_off_grid_homesteading]

Heya, love to see these trouble shooting video. oke so we have to wait for components and then go and test it.

[@TheEmbeddedHobbyist]

Must be very efficient as the output is rated above the fuse on the input. output power 1560W input fuse 6.3A so at 240V 1512W 🙂

[@davidhollfelder9940]

How does a 1 meg resistor get burned out? (The voltages aren’t enough to do that) .. unless the heat came from another component?

[@reneandra9294]

hey Richard, if this is an urgent repair, i would just put a standard opto in there and a separate transistor to the output. maybe a darlington to have the same behavior.

[@LearnElectronicsRepair]

Fortunately this one is not urgent so I ordered the correct part. Thanks for the suggestion though🙂

[@followthetrawler]

Richard, on the little board with the burned resistor and popped capacitor, did you check the black glue for conductivity?

[@LearnElectronicsRepair]

Not yet, but I will remove the capacitor and resistor when the opto turns up so I'll get all the glue off then.

[@30natacha]

i have to fix so many item same at this class D amplifier verry easy to fix check all self sometimes they can be cutted by vibration from the woofer so powwer suply can't start they are -12 and +12 volts outpout can have trouble

[@ianhewitt1858]

Hi Richard. You made a comment regarding the brown/redish large rectangular capacitor on the little board (the one with the faulty opto to the effect that it is dropping voltage. I have also heard 'big clive' make similar comments (particularly when looking at strings of Christmas tree lights) which makes me think that this is done but normally for cheapness and could be better. However, I have tried to look up why you get the voltage drop and from an understanding the circuit point of view, how you would predict what it should be. It is probably the electrical term for this way of dropping the voltage that I am lacking, but it is something I have started to notice and something I know nothing about. Any change of a quick comment from yourself or the great subscribers who are also very helpful with there comments. P.S. Hopping Santa brings me some of those tweezers you reviewed. They are really good. Finally, being I have touched on desoldering, I came across and new cross-bread of disordering tool I have not seen on your channel but may be useful. It fits between using a vacuum desoldering gun and a solder sucker. It basically has the hollow hot soldering tip of the vacuum gun but backed up with a manual solder sucker instead of a pump. Pretty cheap (less than £20) so a bought one and have had great results.

[@SkippiiKai]

It's called a capacitive dropper. It works, but the power factor is terrible. It works like a resistor, but it won't get hot since it's reactive power. EEVBlog has a video explaining how it works and how to do the calculations. It's called something like "mains zener mains capacitive dropper heater" or some combination of those words.

[@Tims_Projects]

I also think this would be a good topic for Richard to explain. Richard explains things in a way I can understand. I looked it up and found two formular showing the output you get when knowing all the values in the circuit. Then I tried to find out how to work out what is need to get an output voltage of my choice, then my brain shut down, haha. But after reading about this circuit, I think I now understand what Richard says, how it detects the voltage range between 110v and 240v. So both those topic would be good for Richard to explain, please. 🙂

[@gadgetmind]

Look for Microchip application note AN954 for a good explanation of these.

[@LearnElectronicsRepair]

@@Tims_Projects I'll do my best

[@SkippiiKai]

​@@LearnElectronicsRepair I understand how the circuit can detect 120 or 240v. And I understand hour capacitors can induce a 90 degree phase shift. What I can not understand is how the circuit can make a 90 degree physical rotation on the mains fuse! 😮 That is a cool fuse holder, though.

[@zedcarr6128]

I would sketch out the opto-coupler part of the circuit and see what it's doing, I'm curious about that part of the circuit myself, TBH. A barbecued 1 Meg resistor is concerning, if that is what its value originally was? Even if it was 325VDC from rectified mains across a 1 Meg, I still wouldn't expect the resistor to BBQ? It would dissipate about 105mW???? 🤔

[@LearnElectronicsRepair]

The coloured bands show it was a 1M0 resistor, I'll make a followup when the optocoupler arrives and several viewers are interested in that capacitor voltage dropper circuit so yeah I'' explain it on paper

[@nasosst3092]

Hi Rick. Seems the end of the high season and more of these badly used audio components coming to the doctor. Seen that in my country also for decades....

[@LearnElectronicsRepair]

Errmmm actually it is the high season here now, our low season is April-Jun

[@nasosst3092]

@LearnElectronicsRepair For us is May to September

[@LearnElectronicsRepair]

@@nasosst3092 It varies from place to place I guess, where are you? For us it's holiday season all year, in the 'winter' is dry and sunny about 22C-25C daytime and 16C or so minimum at night, unless we have a heatwave like right now, it's the second heatwave of November and today was 35C according to the street thermometers. Summer is also dry and sunny but warmer, so generally 28C-32C in the day and night minimums well over 20C... unless of course we get a heatwave then too. We have heatwaves about 10-15 times a year, possibly more. So High season is from around end of September to the end of March because this is the closest destination to northern europe which has year round sunny warm weather and we generally get an older tourist demographic many of whom stay for 3-6 months until european 'winter' ends. Then we get the lull I mentioned Apr-Jun (this is when some bars, shops, and restaurants close for a while to take holidays or do renovation work, but there are still plenty of tourists around) Then July-Aug-Sept is the hottest period and we get a mainly younger tourist base making the place very busy. Other big events that last 7-10 days each attract tens of thousands of visitors are Maspalomas Carnival at the start of March (400,000+ one of the worlds largest street parties!) Pride in May (80,000+) and Winter Pride in November (40,000+)

[@georgeogrady449]

Bright light to doll light then back bright now keep blowing fuse

[@TheEmbeddedHobbyist]

on the little circuit board, i expect that the LED was used as the voltage limiting device. the large cap limits the current to what ever in the circuit limits the voltage. so if the LED was the limiting component if it went open circuit the voltage across the cap would rise to the point where the 16V cap became the voltage limiting component. So would be over driven until it started to consume all the current and get hot. these capacitive dropper supplies will try to go up to the rectified mains voltage if there is nothing to limit the voltage.

[@stevejagger8602]

Ahhh capacitor droppers!! It is a sign of cheapness and lazy design. The cost is on the user when it fails and delivers full mains voltage. These circuits usually lack mains filtering and surge suppression.

[@ianhewitt1858]

I understand big clives expressions better then. Capacitor droppers in one way to do something poorly:-)

[@moulyjeanlouis7302]

MONSSIEUR LE TRADUCTEUR ARETTE DE PARLER COM UN ROBOT C'EST TROP CHIENT!!!!!!

[@Irilia_neko]

Looks like someone buy a Bulk of amplifier from a recycling company