DAS18A 750W Class D Amplifier Repair: PART 2 Why Did The Amplifier Go BANG?
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- čas přidán 24. 05. 2024
- I have three DAS18A Class D Amplifiers to repair. This did not go totally to plan, One of the amplifiers is blowing fuses. Wanna find out what happened? You just gotta press PLAY
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Thank you
Richard
I once slipped whilst working on a broken Roberts R600 radio and the short fixed it! I think the short blew the tin whiskers out of some of the transistors and restored it to life.
Heya, nice part 2. totally following the trouble shooting thought you have. can't wait for part 3
Use a piece of solid coper wire to unsolder multiple legs at once, it will act as a wide iron tip allowing the component to drop out as in the Mr. Solder Fix videos. Flood with solder and bobs your uncle. For more complicated shapes just bend a piece of solid copper wire to fit all legs at once.
That is the beauty of using a GDT(gate-driving transformer). Normally only the components on the MOSFET side of the GDT gets damaged. I totally hate designs where the MOSFETs are driven directly… prime example is that on lots of stuff they drive the gate of Triacs directly from a microcontroller. If that triac blows up, say goodbye to the controller, and with its unavailable firmware, have to repleace the whole PCB just for the cost-saving execise of driving the components directly. I am always relieved when I see a GDT in a circuit. Of course, the GDT is needed in this type of switching topology, but it also makes these kind of Power supplies the easiest to repair… for me at least.
As I understand it the Base/Gate Driver Transformer or a winding on that, in ATX type PSU at least, is also the the aditional L in the LLC circuit. It's good to see we agree on the likelyhood that the driver side of the SMPS output stage is probably OK due to the way it is designed. Repalcement parts ordered 🙂
Great fault finding techniques, keep em coming !
Thoroughly enjoyed and subscribed. Yeah, most of the time my first choice is drag the iron across all the pins while very gently pulling on the device to remove it.
Good measurements and video Richard 👍👍👍👍
All your videos are getting better all the time
49:35 That chip has a vref pin which is a 5V output so you can check the voltage there on that pin and if correct the chip could be assumed working or at least not totally fubar. You could also check the other pins (LO, HO) with scope to see if it is outputting.
Hi Richard, nice logical investigation. Remember that odd 12v supply not referenced to ground? Look closely at the datasheet for the 2092 amp chip and you'll see it needs a bias supply referenced to the -63v supply, I think that'll be for that. Feel for you on this one, I was recently working on a quite similar amp in a powered mixer and slipped while measuring and managed to short out and blow the power supply (which previously was working just fine as one of the 2 amp channels was OK). Finally traced the amp fault to a couple of failed caps but repairing the power supply cost me far more to fix and was entirely down to my clumsyness!
Ah this happens sometimes!
I agree with you. Sometimes when working on a repair bad things happen, not particularly deliberately, but that is how it is. You know that I am quite happy to show what happens in real life (it is so easy to edit this stuff out and I suspect some YT channels will do just that) but hey this is the real world and I'm grown up enough to own it and take the flack from publishing it if that is the result. I didn't mention in this video but I won't charge the customer for that part of the repair. He probably wouldn't know the difference but he's a good customer. Thanks for the info on the non ground referenced 12V supply. I didn't investigate it further, just kinda realised what it was, for whatever reason
I use short lights for dc as an auto electrician 12/24v. Sometimes you just need more current available so add an extra bulb. I use 65w halogen headlight bulbs, sometimes 2 depending on what I'm testing.
I was kind of excited to see this part of the repair where we dig in a little bit deeper... And I was pleased to see that when I turned on my computer and went to CZcams that this video was already posted... There were a lot of things that I saw in this video, some things made me think about the overall quality of the amp and why they did things the way they did, these are mostly visual things like all the glue... we've discussed why they do add glue but it sure looks terrible, the silicone on the inductors? I'm assuming that the coils on the inductor they wanted to make sure they don't move around? the wire loops stay in place was that the idea? also Richard this kind of bothers me, what I saw,.... The mounting of the transistors with the screw and a nut, that's okay with me but the Type of Nut they used am I seeing a spline washer??? directly touching the silicon structure of the transistor or MOSFET devices... To me... That doesn't seem like a good idea, for one you could over tighten it and damage the component, you could also have a certain amount of torque on the screw and maybe things are working fine but over time that pressure and the way the spline washer cuts into the material could cause a problem. I don't want to go overboard on this subject but it just seems like a very poor decision to use a spline washer, spline washers are used to bite into materials in order to keep the fastener in place but were talking about transistors and MOSFETs it just doesn't look like a good idea. A flat washer makes more sense to me, and if some engineer is concerned about the fastener loosening overtime okay, Then put a spline washer under the flat washer to hold things together... 🙂🙂🙂 I'm going to exercise some patience in waiting for the repair components to be delivered and we continue. If I've said anything that's worth commenting on please do so in the next video about our continued analysis and repair of this Subwoofer Amp. 🙂
Recently I had a bridge rectifier that tested fine in diode mode, and the psu actually powered up but with issues, after lots of testing, I got the thermal camera out and that bridge rectifier was on fire!
Changed it out and problem solved, very strange
Before repairing anything, find cause of the Subwoofer’s speaker cone failure. The torn paper or foamy Surround aren’t the cause, they are the effect. Almost always, a torn corn is the result of a loose retaining ring/“basket gasket”. Next likely cause is Enclosure Over-Pressure. If the subwoofer is in a ported box and a port inhales an object, air flow can be stopped and something has to give… Another cause is if two subwoofers are in one enclosure and they either are wired or fall out of phase secondary to amp failure or a few other in circuit failures.
I know everyone is yelling “Nuh uh… It’s from over-driving(over powering) the speaker…” If it’s a mid or tweeter or even a woofer, sure. But Sub-Woofers are designed to be pushed hard to drive those ridiculously low bass notes that make wax run out of your ears.
Surprisingly, one of the best methods to repair a Sub-Woofer’s cone(paper like material) or the “surround”(flexible bit around circumference of the cone) is to use a piece of drywall mesh, spot of glue to hold the mesh and finally, clear Flex Seal. Like anything, prep is key to yield a quality, functional, long lasting repair. Use a flexible glue and use sparingly. To keep the movement of the cone as uniform as possible, extend the repair in a way that spreads Flexible Seal around the outer most circumference of the cone. To test the repair, the all time best bass album has to be “Digital Bass”by Bass 305. Rinse, Lather, Repeat….
Hi Richard - another great video. What was the reason for the 100 ohm resistor reading 1 ohm on both boards?
Hello there, i love the fact that you do videoes on creating Equipment for the home gamer electronics lab, if possible could you look into making a mains isolation transformer 230v/230v from reused parts from commen things. Thanks.
It looks like this power supply has dual mains input, 115/230Vac, I think this is set by the red switch near the power switch, is this set correctly for your country?
Yes, I was thinking this too. Can we see that on the other amps?
Not everyone has a desoldering gun but was it just me wishing you would use a simple solder sucker instead of poncing about with yards of too-small-wick to clear solder from those fat transistors? Sometimes us oldies have methods that still work, even if it does mean having to sweep the dusting of solder bits off the floor :-)
IMHO if any given method it works for you then go for it 🙂 I guess to some extent I just like to vary the way I do things when making videos just to show there is more than one way to get the required result. I also discuss the method of heating all legs at once without removing any solder and pulling the device directly from the board and then go on to demonstrate that on the amplifier PCB. How do you rate that method?
@@LearnElectronicsRepair the heat and pull method works fine but if the device is too big and has a metal tab your fingers may suffer! In my experience say "ow" and swearing does help though :-)
I used to hate solder suckers until someone gave me an Engineer ss-02 sucker. It has the silicone tube that gets a good seal around the area being sucked. For me it was a game changer on tricky desoldering jobs.
How many watts is your bulb please ?....cheers.
DAS Destruction after Sound
how does the 115/230 switch connect into the switch mode power supply
Oh I really should make a video about that 🙂
@@LearnElectronicsRepair nice, because back in the time of normal transformers it was logical to enable different sections of the primary side, and most smps are auto range.
Does anyone else find themselves shouting .. "its not a short its a resistor across the winding of the output transformer'
You cant hear me shouting from here can you?😂
@@gr8pr4mr No need to shout, I came to the same conclusion in the video. I didn't shout either... 😉
@@LearnElectronicsRepair :)