Jump to content

Hifi amp basic repairs course 101


Recommended Posts



A good structured approach, good luck with your search. Might need to refine your search a little depending on what era (vintage?) of equipment you are interested. Most vintage will be discrete maybe throw in the odd opamp or display driver... However AVR's and the like will be microprocessor controlled with a fair sprinkling of other IC's. Generally the AVR's are a difficult repair. Important to be able to follow the schematic, many freely available on hifiengine.

Link to comment
Share on other sites

I think the basic thing to learn first is how to use a multi meter just to see if there is power going to sections of the circuitry, a lot of troubles start there.....no power = no work

 

Then probably measuring capacitors and the like to see what value they currently are, compared to what value they are rated at in the circuit diagram, not unusually to have several of one type and one has failed.

Those basics should help you sort out what's amiss with things like Tube amps and 70's Japanese amps, or anything else that was pretty much hard wired.

 

Circuit board level diagnostics is several levels up from that and needs more expertise and more equipment.

 

Pity the old Dick Smith stores aren't around any more, they used to have a series of books that you could buy to teach yourself this stuff.

 

You could do worse than to watch this and it's companion videos

 

Edited by Tweaky
  • Like 1
Link to comment
Share on other sites

Thanks guys for your helpful replies. I have been picking up all sorts of skills from Youtube over the last few years, and can generally cope with small maintenance of equipment like cd players, turntables but recently, had a mishap with blowing up my MF A1 amp due to accidentally having speaker wires touching each other. Tweaky's suggestion of a multimeter is a good first step and I will source one pronto. The next thing is to see if I can find a schematic for the amp . Just how did you guys get started in the first place - formally through courses or learn as you go?

Link to comment
Share on other sites



2 minutes ago, Audiofan231 said:

Thanks guys for your helpful replies. I have been picking up all sorts of skills from Youtube over the last few years, and can generally cope with small maintenance of equipment like cd players, turntables but recently, had a mishap with blowing up my MF A1 amp due to accidentally having speaker wires touching each other. Tweaky's suggestion of a multimeter is a good first step and I will source one pronto. The next thing is to see if I can find a schematic for the amp . Just how did you guys get started in the first place - formally through courses or learn as you go?

I wouldn't feel bad about the mishap with the MF amp, I sent a MF amp off to a well known repaired in Sydney many years ago to fix a faulty phono stage and he did exactly the same thing you did, and that was after me giving him the MF amp in it's original box with manual that specifically warned not to let this happen.....it's basically the only instruction in the manual.

Link to comment
Share on other sites

33 minutes ago, Audiofan231 said:

Thanks guys for your helpful replies. I have been picking up all sorts of skills from Youtube over the last few years, and can generally cope with small maintenance of equipment like cd players, turntables but recently, had a mishap with blowing up my MF A1 amp due to accidentally having speaker wires touching each other. Tweaky's suggestion of a multimeter is a good first step and I will source one pronto. The next thing is to see if I can find a schematic for the amp . Just how did you guys get started in the first place - formally through courses or learn as you go?

I am sure everyone started by blowing up an amp - maybe not exactly MF A1 ...

  • Like 1
Link to comment
Share on other sites

26 minutes ago, Audiofan231 said:

Thanks guys for your helpful replies. I have been picking up all sorts of skills from Youtube over the last few years, and can generally cope with small maintenance of equipment like cd players, turntables but recently, had a mishap with blowing up my MF A1 amp due to accidentally having speaker wires touching each other. Tweaky's suggestion of a multimeter is a good first step and I will source one pronto. The next thing is to see if I can find a schematic for the amp . Just how did you guys get started in the first place - formally through courses or learn as you go?

Pretty simple the way I did it. Originally a 20 month full time course as a Radio Tech in the RAAF in the early 70's, starting with basic electrical theory (valves too :) ) and progressing up to RF theory, then 30 odd years of practical and courses while working on electronics in the RAAF and as a contractor, then another 7 years running my own repair business. Then I slacked off and did some Auto Elec work for a few years.. Oh and some TAFE courses over a couple of years, to get an Advanced Diploma of Electrical Engineering.

  • Like 1
Link to comment
Share on other sites

7 minutes ago, Decky said:

I am sure everyone started by blowing up an amp - maybe not exactly MF A1 ...

Those early MF A series amp were notorious for this exact failure.

Most well designed amps wouldn't really suffer if the + & - cables touched momentarily.

I remember a forum member explaining to me that he found it amazing that these MF amps were actually allowed for sale, he deemed some parts of their circuitry down right dangerous.

 

That's one thing you can't learn quick enough if thinking of doing electronic repairs, where NOT to stick your hand, or make sure only the back of your hand can touch anything live, that way the electric shock if any won't make your hand clamp around the thing that's live, not allowing you to let go.

 

I'm glad I heeded this advice when adjusting the yokes on a old 3 lens CRT projector, I doubt I would be typing this otherwise.

Link to comment
Share on other sites

Guys, it makes me feel so much better already knowing that blowing up amps is not only for idiots like me. Still, my tender heart still feels the pain when it happened to me. Seems like, in the world of tweaking with hifi, if you have not blown your amp or speaker, you are not really an enthusiast.

I'll sleep better tonight for sure.

Link to comment
Share on other sites



You can spot DIY electronic fixers and builders when they compare soldering iron burns ?

 

That's another thing you need to master, soldering and de-soldering, which if repairing is even more important to learn to do well.

I'm pretty sure I've seen a post on how to do this to 'no fail' military spec by bob_m_54, who has already chipped into this post already, you might want to ask him where on the forum it can be found.

 

A good Multimeter with different probe sizes and alligator clip probes is what you want, you can do a lot with a good one, and can be frustrated if you skip on a lesser one.

 

Likewise soldering irons, sure you could buy a basic one that will do small jobs, but a Soldering Station with variable heat settings is what is worth getting, again with various sized iron tips.

 

Both items should last you many years if you buy decent units in the first place.

  • Thanks 1
Link to comment
Share on other sites

Bob, if I can wind back the clock,  I would go by your way and start with the basics first. Don't think the RAAF will accept 60 year olds like me anymore, would you?

 

Tweaky's comments re: flimsy design of the MF, plus the heat that it generates makes me wonder why it became such a darling with the hifi world. In all honesty, I find the vintage NAD 3020 a much more robust amp, able to drive all my speakers much better, and it sounded just as good to my ears. If anyone asks me, I would tell them to keep away from the A1.

 

 

Link to comment
Share on other sites

4 minutes ago, Audiofan231 said:

Tweaky's comments re: flimsy design of the MF, plus the heat that it generates makes me wonder why it became such a darling with the hifi world. In all honesty

 

 

British HiFi press trying to push a British built class A amp for the masses. [they should have stuck with the unfashionably clad, but ultimately better designed and robust Sudgen ]

At the time of the MF A1 the Krells were the darlings of the HiFi scene, the old KSA50's and 100's.

If you didn't have the cash for the new fashionable class A amp technology coming from America, here is the 'High street 'UK's version, although this was before the UK had to have it's electronic conform to the specs designated by Belgium.....hence the shonky design, it was designed and built quickly to a price point to take advantage of HiFi fashion at the time.

 

I forgotten how many times I've seen forum member Yamahaman has had tried to sell on his Krell K.A.S amps, nice amps, but total overkill and uber expensive to run with today's electricity prices.

  • Like 1
Link to comment
Share on other sites

57 minutes ago, Audiofan231 said:

I find the vintage NAD 3020 a much more robust amp,

NADs of that vintage used cheap parts (caps, trimmers..) also they cut some corners with parts marked but not loaded into the pcb. If the 3020 is original then it's over due for a recap and basic health check (bias...). Also suggest reading up on spkr protection, you can get basic kits off the bay from china for about $15-. It only takes one failed output transistor to smoke your spkrs... I've refurb'd 3 x 3020's and a few others, they're ok if you are on a tight budget, I find they lack in sound stage, general tones, dynamics are ok.

 

Consider an oscilloscope, it will help troubleshooting. This can be a significant investment, maybe as an interim measure, they sell toy oscilloscopes again on the bay for about $40-, these are ok for binary yes/no testing

Link to comment
Share on other sites



1 hour ago, Tweaky said:

You can spot DIY electronic fixers and builders when they compare soldering iron burns ?

 

That's another thing you need to master, soldering and de-soldering, which if repairing is even more important to learn to do well.

I'm pretty sure I've seen a post on how to do this to 'no fail' military spec by bob_m_54, who has already chipped into this post already, you might want to ask him where on the forum it can be found.

 

A good Multimeter with different probe sizes and alligator clip probes is what you want, you can do a lot with a good one, and can be frustrated if you skip on a lesser one.

 

Likewise soldering irons, sure you could buy a basic one that will do small jobs, but a Soldering Station with variable heat settings is what is worth getting, again with various sized iron tips.

 

Both items should last you many years if you buy decent units in the first place.

Maybe this post? I think I may have done one once before too, but can't find itl

https://www.stereo.net.au/forums/topic/27524-diy-audio-what-are-you-building/?do=findComment&comment=4557865

Link to comment
Share on other sites

There are a lot of online structured resources.

 

I had a look at the syllabus for a couple and I'd suggest:

https://www.edx.org/xseries/mitx-circuits-and-electronics

 

You could probably skip some of the maths but I would highly encourage you to do the maths. It will help you get a better understanding. If you do skip the maths you may still pick up a few things. 

 

There is a lot options on udemy but its not free unless you find a coupon.

 

I'd say to really start with a good foundation you need to be able to:

  • Identify components
  • Understand what each type of component does (at least roughly)
  • Know and be able to measure various properties
  • Have the equipment for measurements
  • Soldering and ideally desoldering equipment
  • Be able to read circuit diagrams
  • Be able to understand the circuit diagrams, even if its just one portion at a time

 

I started my education with some basic tinkering and then a university degree. 

 

The hands on practice is important but that is a little bit easier to obtain.  There are reputable guides to follow and the rest is practice. It always helps to understand why you are doing something so that basic knowledge is helpful.

 

I am very glad to have had structured education. There is a lot on the internet that can steer people off the right track. Its good to be able to understand the basics and make decisions on whether the information is off the mark, if its spot on, or if its just beyond one's current understanding at the moment.

 

It is always good to have someone take genuine interest in learning something within their own interest.

 

Alternative pathways (I'd recommend the edx pathway above but this one is free):

https://www.coursera.org/learn/linear-circuits-dcanalysis

https://www.coursera.org/learn/linear-circuits-ac-analysis

https://www.coursera.org/learn/electronics

 

edit: edx one isn't free.

Edited by gwurb
Link to comment
Share on other sites

7 minutes ago, bob_m_54 said:

Maybe this post? I think I may have done one once before too, but can't find itl

https://www.stereo.net.au/forums/topic/27524-diy-audio-what-are-you-building/?do=findComment&comment=4557865

That sort of seems like the one I meant.....long time since I first read it.

 

If not, what would you add, or edit to that post to make it  your definitive guide on the subject.....nobody knows better or has as much experience at this forum.

 

It's Knowledge like this I would like the forum to have as a library.

Link to comment
Share on other sites

55 minutes ago, Tweaky said:

That sort of seems like the one I meant.....long time since I first read it.

 

If not, what would you add, or edit to that post to make it  your definitive guide on the subject.....nobody knows better or has as much experience at this forum.

 

It's Knowledge like this I would like the forum to have as a library.

Not much to ad to that post, but there is a lot to learn, especially with newer solders and fluxes available. But that NASA guide, if a little long winded does cover the main points on making good solder joints.

 

I think there are a few guys on here that have had plenty of soldering training and experience on here though, they might like to ad something.

 

I looked around for another more modern guide, but even though there are heaps online, only a few of them are much chop. And add nothing to the NASA guide, except some may have some decent photos. That second link in the post has some pretty good pics of acceptable and reject solder joints, but no explaination of what the causes are.

Link to comment
Share on other sites

Wow, the feedback from you guys is much appreciated.  From what I can gather, there is no short cut to learning what I need, so I am now looking into learning from first principles before I get myself into too much trouble. Just found an affordable online site Udemy.com, and they offer something ( https://www.udemy.com/course/crash-course-electronics-and-pcb-design/) which I think could be appropriate first step for learning some basics for a newbie like me. Any comments on whether it is appropriate from anyone of you would be most welcomed. 

Regardless, looks like a trip to Jaycar next week to stock up some basics. That Hakko soldering station looks great, but I will stick to the basic one I have for now. 

 

Thanks

Link to comment
Share on other sites



Just got alerted to a book titled: Hands on Electronics - A One Semester Course by Kaplan and White. Seems like what I need to start with learning about all things raised by you guys. On looking through the sample videos of the Udemy Couse I mentioned above, it is probably too theoretical,  and entrenched in PCB analysis and design, so I will give it a miss.

Cheerio

Link to comment
Share on other sites

Just got alerted to a book titled: Hands on Electronics - A One Semester Course by Kaplan and White. Seems like what I need to start with learning about all things raised by you guys. On looking through the sample videos of the Udemy Couse I mentioned above, it is probably too theoretical,  and entrenched in PCB analysis and design, so I will give it a miss.

Cheerio

Link to comment
Share on other sites

If you prefer a book to a course:
https://core-electronics.com.au/getting-started-in-electronics.html
Here is a starting point..

 

The thing with audio amplifiers is if you replace 1 for 1 then you don't need as much knowledge. If you start to troubleshoot and fault find then you are dealing with electronic circuits. It doesn't matter that that they are audio circuits, in that audio circuits are not NOT electronic circuits. So electronics basics are really needed to troubleshoot and fault find.

 

Link to comment
Share on other sites



  • Recently Browsing   0 members

    • No registered users viewing this page.




×
×
  • Create New...
To Top