Dynacord Powermate 600 Powered Mixer, two channels not working. Can we fix it? Mixer Repair

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@binaryguru 7 ай бұрын

As soon as I saw that resistor burn up after you put that wire, I guessed right away it was caused by a shorted cap. Great video!

@nasosst3092 7 ай бұрын

Thanks for this video Rick. The black capacitor was obviously the reason for all this. I saw the culprit from the beginning but I couldn't spot the bad 10Ω resistor. Some remarks: A) when repairing an audio console check also the mic inputs. Line input bypasses the mic input so checking with line audio sometimes gets tricky. I would see that in ch2 for a start, since the customer (probably using some mic for the Elvis show) said that ch2 not working. Probably using both dynamic and condenser mic to check behavior with 48V phantom. B) as some other comment suggests it is good to check with clean frequencies like 80, then 400, then 5K Thanks again for everything. You are our superhero

@LearnElectronicsRepair 7 ай бұрын

Thanks, actually Elvis was the guy who sold the mixer so he would have been using it previously, but you are correct I should have tested those.

@nasosst3092 7 ай бұрын

@@LearnElectronicsRepair thanks for the reply Rick.

@DracoMcGuyver 7 ай бұрын

Richard, On that chip that you could not find data it is the first number "072BDE" that you should have used. The number that you tried is the manufacturing code, possibly indicating date of manufacture. This part is a JFET op amp for audio.

@stevosteve 7 ай бұрын

Yeah, I spotted that as well 👍

@stevosteve 7 ай бұрын

Yeah, I spotted that as well 👍

@lonndawg7554 7 ай бұрын

To me this was a great repair... In the sense that I came across one of these mixing boards at a garage sale, and it had a note on it broken not working... Now it's a piece of equipment I didn't think I could use because I have no band equipment that uses that type of connections, but I was curious as to what it looks like inside. in this video gave me a pretty good idea of the structure of these multichannel mixing boards. I think we learned a lesson on doing a little bit more about careful component inspection looking for something that doesn't look right... But in this case I would probably lean towards the fact that we are making a video and don't want to have too much idle time... If we would have found some of those burned components early in the video who knows how that would have changed the discussion and the technique for repairing and finding the fault I still thought the method and the discussion was informative. Another question I've had lingering in my mind is where do you get your schematics if you decide you need one... Sometimes looking for them in Google kind of leads to nowhere even if it's a schematic that you think should be available and in some cases making a purchase for the schematics, but maybe more importantly do you have your own personal kind of go to resource when you have to spend the money for a set of schematics I know this would be something you would purchase if you were kind of stuck, but again sharing information and expressing ideas for repairs is always something to go over with the participants in this channel. There are potentially many ways to fix things and hearing an idea from someone could be very helpful. Also, what I really enjoyed in this video was you tracing down an audio signal, in the beginning of the video I kind of thought we were going to search for the failure in a more traditional way just checking components, but I was so pleased to see that we injected a regular audio source which really made me think for a few minutes, I would have probably gone the more complicated??? Ha ha ha method of using a signal injector or some kind of tone generator... But you showed me what would happen if he just put in an audio signal you showed what you might see on the scope which I expected but again I was thinking inside the box... Ha ha ha it takes time and experimentation to pick up these tips. 🙂

@thelastofthemartians 7 ай бұрын

Greetings from Australia. A trick you can do with multi channel boards like this is to look at the board and cross your eyes until the two channels overlap. The differences between them (e.g. burnt or missing components) stick out like dogs balls. Takes a bit of practice though.

@deedeelabricolade 7 ай бұрын

Weirdest shit I read this year but yeahr... seems a hell of a good idea, free and I already have strabism. I'm in! Thanks for that tip, I guess

@Tims_Projects 7 ай бұрын

haha 🥸

@LearnElectronicsRepair 7 ай бұрын

@@deedeelabricolade Yeah sounds weird bur who knows! Is this a bit like seeing hidden objects or faces in those weird images made up of coloured dots?

@deedeelabricolade 7 ай бұрын

@@LearnElectronicsRepair ah yes those images you have to unfocus on to see 3D stuff appearing, that was fun! I'm currently moving, can't test anything but from the top of my head, if the circuit is symmetric... It's kinda genius. Hats off and thanks for sharing this @thelastofthemartians

@Foobar_The_Fat_Penguin 7 ай бұрын

Out of curiosity: Is there are specific reason why you always test with music when using the scope? I would have assumed that a pure sine wave would be a better test signal since it not only allows you to spot whether the signal is present or not but also whether it's distorted in some way - which might be another helpful clue.

@stevosteve 7 ай бұрын

Oh the memories of many hours trying to find the source of a 'slow to rise' 10volt to all 0-10v outputs on a Zero88 Sirius 24 lighting desk. The hours I spent comparing one result against another, only to find the second test was different simply because "time" had passed between the tests, and the "time" was allowing the psu source to rise. Oh the pain. BTW, what was my fault in the end ? . . . . no idea yet as I had to turn the project into a 'come back later and try again' for the sake of my own sanity. Still trying to get my head around the multiplexed signals feeding the 24 dimmer slide pots 😢

@Lightrunner. 7 ай бұрын

Hi Richard 🤗🤗 Good work and repair. A nice fundamental piece of elektronic👍👍👍 You didn't look for the bleeb 😭😭 how dare you.......

@Dutch-linux 7 ай бұрын

so on timestamp 26:02 when there is no connection to the power rail of that channels opamps a good bet be a resistor (maybe the one that was flaking off) or maybe a bad trace ... you could bridge the power from a working rail to the bad rail from one opamp to the other ... if it starts working then you know where to look ....

@stevosteve 7 ай бұрын

Agreed. Personally I was expecting to find a burnt pcb track due to the short. When Rich bridged the +ve line feed I thought it was another part if the pcb track going up in smoke . . . . . resistor burn is an easier fix (especially as some pcb have central non-accesible track layers these days)

@gregbennett2437 7 ай бұрын

Hello Richard at times stamp 37:17 if you look right below the component that your probe is on at R34E there is a burnt resistor May mean nothing but it looks pretty bad from here hope this helps.

@Dutch_off_grid_homesteading 7 ай бұрын

Heya, nice repair love it. wouw I saw the burned capacitor but I didn't see the burned resistor so I can say I'm learning nice

@GregM 7 ай бұрын

Same here I saw what appeared to be scorch marks on the neighboring cap

@Dutch-linux 7 ай бұрын

timestamp 36:30 and yess seee Dutch was right again !!!!! that is a tantalum family of capacitors and thet tend to short... LOL Richard you and I are real professionals in this 🤣

@LearnElectronicsRepair 7 ай бұрын

Hehehe

@UberAlphaSirus 7 ай бұрын

lol. i recently bought a mixer to do my daughters 18th. The manual was useless, so I had to open it up to figure out how it works. the soldering is shocking, dry joints galour. Good thing with these is if you have a good channle left, you have somthing to go by.

@anthonyshiels9273 7 ай бұрын

A 400 Hz tone is easier for testing audio signals because it is not "random".

@LearnElectronicsRepair 7 ай бұрын

Hehe true, but Northern Sould sounds nicer 😋

@anthonyshiels9273 7 ай бұрын

@@LearnElectronicsRepairIf you listen to Big Ben you will HEAR a musical tone of 440 Hz that corresponds to A above Middle C. This frequency is not listed on a spectrum of the sound of the Bell.

@Dutch-linux 7 ай бұрын

timestamp 36:02 so there is a short somewhere and now you got to also look for the resistor that is burned for that channel !!!! but it does not mean that a opamp is shorted you could as well have a cap that is shorted if you would of zoom in more so we could really see what components there really are it be visually better to diagnose and at the looks of it with the ic's that are used it is a very cheap built mixer not a high end one for sure

@mitkothemacedonian 7 ай бұрын

The opamp is tl072, dual, jfet input.

@andygardiner6526 7 ай бұрын

Ok, I admit to screaming black cap at the screen! However the no short readings on the psu confused me ...

@LearnElectronicsRepair 7 ай бұрын

Yeah me too. It wasn't a short, it was just over 40ohms. And my Fluke on Continuity just sees anything over 40 ohms as open! This is why the resistor didn't just burn up immediately, because it wasn't exactly a short. The only excuse I have (and not a very good one admitedly) for not realising the black cap was the problem sooner is that I have to manage the camera / recording system which uses two monitors both of which I need to keep an eye on, look at the repair job which is genuinely 'live' repair work with no prior rehersal, figure out what I'm gonna try next, try to second guess what you guys will tell me I should have tried next if I didn't 🤭 try to remember what I already did and keep up a running commentary all at the same time 🤪 So my concentration is not always focused where it should be.

@warwickbunn1250 7 ай бұрын

Ah, I didn't realise you are juggling all the tech and the story you are creating as well as the actual fault finding 😜 So having an audience doesn't always help 😂 But I am pleased to hear your main repair tool is back in use ... namely THE Northern Soul music 🎶 😊 Great video Richard 👍

@andymouse 7 ай бұрын

This is not a criticism but ! I am surprised that a guy who does what you do hasn't got leads and loads for amplifier testing to hand and a nice 1Khz tone. I would have thought amp's would be a big thing as you live round a load of bars. Nice fix !....cheers.

@Dutch-linux 7 ай бұрын

at timestamp 24:25 at this point i will bet on the opamps but to make sure see what the signals is at the output of the transistors !!!

@Mark_C1 7 ай бұрын

@ 7:03 C31B Looks like it’s failed. Only just started the video though 😬

@vaccarioou22 7 ай бұрын

Puzzled about why those particular components failed - any ideas ?

@Dutch-linux 7 ай бұрын

Richard useually when there are 3 bad channels it is most likely not the pots as it be weird that the pots on the 3 channels go bad at the same time !!!! so not sure why you waste time there.... in my experience it be transistors or opamps .... or a combination of the 2 ... there the opamps share 2 channels I think it wont be the opamps then likely 4 channels would be bad.. there every channel has its own transistor bank i would lean towards that... this is at timestamp 9:50 by the way do you even know if the line inputs on the channels work ? or is it both the mic and the line that do not work on the channels ? as that makes a big difference to troubleshoot ... when I look at this mixer the transistors the 4 pairs do the mic pre-amplification and after that the opamps do the line and the mic so once you know which part aint working you can elimitate 80% of what could be wrong !!!

@LearnElectronicsRepair 7 ай бұрын

Also I got that wrong and there were two dead channels