Hifi amp basic repairs course 101

[gwurb]

Just now, Audiofan231 said:

Hi gwurb, that edx course looks very interesting, but at $638,  a bit too pricey for me at this stage.

Thanks buddy.

Sorry, my bad. The second options are free.

[gwurb]

1 hour ago, Audiofan231 said:

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

 

For cheap but good soldering Iron https://m.banggood.com/FX-951-220V-EU-Plug-Solder-Soldering-Iron-Station-p-932706.html

 

Multimeter

Jaycar multimeters are ok, this was prescribed for our course: https://www.jaycar.com.au/ip67-true-rms-autoranging-cat-iv-dmm/p/QM1549

If you go for a better multimeter then Bremen BM235 from  https://www.welectron.com/Brymen-BM235-Multimeter_1 

is a great option. 

You could do with less but for electronics you want mV and mA, and ideally uA.

I would say you need an oscilloscope (depending how broken something is) but I think that is best commented on by someone else who repairs for their main job.

Get yourself some safety goggles for soldering and a fan to blow any smoke away and out the window.

 

There is more but that would get you started.

 

edit: I would highly recommend temperature controlled soldering iron. If you have the right temperature set you are more likely to succeed.

Edited August 15, 2020 by gwurb

[mbz]

A tip on reading/following the schematic.
Download the service manual for the Luxman SQ-505X from hifiengine.
Schematic is very simple, flow is from left(RCA's) to right (spkrs)
and divided into stages and boards. Look for PRE-OUTS/MAIN-IN that
indicates the pre/main boundary. Left channel on top, right channel
(a duplicate so not completely shown) underneath, separated by the
power supply. As simple as it gets. Marantz receivers of that era
are the other extreme, put together by a madman(?) Point is "all"
amps will have a similiar structure so if you are overwhelmed then
revert back to keep it simple.

 

Hint, some amps even show the audio path, typically for the left channel,
as a bold/highlighted line, eg, Yamaha CR-2020 from hfe.

[Audiofan231]

Hi gwurb, that course you bought the multimeter for - is that the edx one you recommended earlier?

For now, I am giving Banggood a miss, as my last ebay purchase from China is yet to arrive after many months - is it lack of flights or is Aust Post the culprit?

Just for my info, is a 220 V soldering iron ok for use in Australia?

 

Looks like my intended purchase of a Pro-ject turntable will have to wait for a while.

 

Thanks everyone for all your helpful input.

[Audiofan231]

Thanks mbz for that lead to hifiengine.

[bob_m_54]

Pace have a series of soldering technique videos too, that look pretty good. We used to use a lot of Pace gear in the RAAF back when I was there.

 

There is a series of 9 basic soldering videos, and another series of 8 rework videos.

Paceworld Channel.

[bob_m_54]

10 hours ago, gwurb said:

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.

 

Sorry, I don't understand your statement "audio circuits are not NOT electronic circuits" ?

 

But I agree, as you say, quite often you are replacing like components for like, when you find an obviously damaged part. But what you do need to know is why the component failed in the first place, and what other parts are likely to also be damaged, to avoid a repeat performance.

 

So, to do this, a good understanding of electronic circuit principals, and how to read schematics is really necessary. And in many circumstances you won't have obvious visual indicators, so you will need to rely entirely on your fault diagnosis skills.

 

Of course you do get common faults with particular brands and models, and you can often find information on these via google and youtube etc, which is a luxury we didn't have 20 years ago. A lot of repair techs would have their own log book of common faults though, and we even did this in the RAAF, back in the early days (the old "good guts" book). And I bet there are still a lot of blokes around that remember the C410 faults in NEC CRT TVs.

[gwurb]

48 minutes ago, bob_m_54 said:

Sorry, I don't understand your statement "audio circuits are not NOT electronic circuits" ?

 

But I agree, as you say, quite often you are replacing like components for like, when you find an obviously damaged part. But what you do need to know is why the component failed in the first place, and what other parts are likely to also be damaged, to avoid a repeat performance.

 

So, to do this, a good understanding of electronic circuit principals, and how to read schematics is really necessary. And in many circumstances you won't have obvious visual indicators, so you will need to rely entirely on your fault diagnosis skills.

 

Of course you do get common faults with particular brands and models, and you can often find information on these via google and youtube etc, which is a luxury we didn't have 20 years ago. A lot of repair techs would have their own log book of common faults though, and we even did this in the RAAF, back in the early days (the old "good guts" book). And I bet there are still a lot of blokes around that remember the C410 faults in NEC CRT TVs.

My comment relates to what I read on the regular enough basis when people write about audio equipment. There is writing as if an electronic component behaves like a different component in an audio circuit. For example as if a transmission line (i.e. a pcb trace) has some unique property when its an audio circuit as opposed to when its in an VLF data circuit. Its behavior and properties are still the same. The considerations vary with frequency but the fundamentals are still the same. But the effects that the fundamentals have on outcomes may need slightly different consideration for audio, considerations that are not required for VLF data.

 

Maybe some of that stems from shortcut rules? For example when I think of resistors I tend to think of wirewound vs metal film vs ceramic vs ... I remember that wirewound would have more inductance and some phase shift compared to a metal film, etc. But that is a shortcut rule. There are things I don't tend to think too deeply into such as resistor thermal noise partially because there are general rules to make life simpler and I don't want to do the maths all the time But I do know that the shortcut rules can and do break down so thinking of the general rules as universal basics is flawed. I think that is a skill in itself; know when a shortcut rule is applicable and recognise when one needs to revert back to basics.

 

I think its best to think of audio circuits as electronic circuits and remember that there are extra audible considerations to take into account, but that's true to any application specific considerations. The basics are still the same.

 

Your comments are spot on. Know the basics and then learn how to apply them to particular context.

[gwurb]

5 hours ago, Audiofan231 said:

Hi gwurb, that course you bought the multimeter for - is that the edx one you recommended earlier?

For now, I am giving Banggood a miss, as my last ebay purchase from China is yet to arrive after many months - is it lack of flights or is Aust Post the culprit?

Just for my info, is a 220 V soldering iron ok for use in Australia?

 

Looks like my intended purchase of a Pro-ject turntable will have to wait for a while.

 

Thanks everyone for all your helpful input.

That jaycar multimeter was prescribed for the introductory electronics courses in my university electrical engineering degree. They deemed it good enough for all other electronics courses. There was other equipment required and more multimeters for power courses but electronics were covered by that jaycar one. The backlight and data hold were nice features. I didn't love that multimeter but it worked and the display was big and easy to read  Some people had other multimeters because they knew enough before the course as to what they would need. There was a baseline, as in no one used a multimeter below a certain level as it just didn't cut it for electronics.

 

I have had good experiences with banggood and poor ones with aliexpress. My ebay ones from China have been hit and miss. I needed to replace a broken soldering station a couple of months ago and didn't have a budget for local and non-knockoff. Took about 3-4 weeks to arrive. Works well. It's not Hakko  The original Hakko is a lot more expensive. I did do one thing with that station after I got it. I opened it up, checked the PCB and wiring. It was fine. I took a wooden tooth pick and flicked off some solder drops from the PCB but looking back it wasn't necessary as there were no shorts. If you really wanted to do that it's pretty simple in that if there is no component but there is a drop of solder just use a soft enough item like a wooden tooth pick to move the solder drops.

 

The temperature control really helps. Also, that style of station where the soldering 'tip' is a whole heating element means that the temperature is more stable as the heat is better transferred to the tip. But any temperature control where there is an actual temperature value (analogue or digital) would be my recommendation for electronics.

 

As far as that soldering station goes and 220V... for an official answer you would need to ask an electrician about what the current regulations say  I am happy using it based on what I know. But that is based on the fact that it's a soldering station + there is tolerance within Australian voltage supply + there tolerance within the station's transformer + there are circuit breakers + there is a fire extinguisher. If in doubt speak to electrician and be on the safe side. I am not sure about anyone else but I would say that a fire extinguisher suitable for electrical items should be located within all electronics workshops. I have a small one.

Edit:

It can cost a bit of money to setup a workspace. I remember years ago speaking to a friend about bicycle gear. I was asking him about buying my first helmet that I bought myself. Along the way he said 'How much is your head worth?'. So my head has no need for a top of the line lightweight helmet but it needs a level of protection.

 

Similarly some things are needed for workspaces in my opinion. Like I use a simple ESD mat: https://www.jaycar.com.au/anti-static-work-place-desk-mat/p/TH1783 . I use a slightly more expensive strap as it's soft and I don't like the chaffing from the hard bands.

Edited August 16, 2020 by gwurb

[Audiofan231]

Much obliged to both of you, Bob and gwurb.

[gwurb]

6 hours ago, mbz said:

A tip on reading/following the schematic.
Download the service manual for the Luxman SQ-505X from hifiengine.
Schematic is very simple, flow is from left(RCA's) to right (spkrs)
and divided into stages and boards. Look for PRE-OUTS/MAIN-IN that
indicates the pre/main boundary. Left channel on top, right channel
(a duplicate so not completely shown) underneath, separated by the
power supply. As simple as it gets. Marantz receivers of that era
are the other extreme, put together by a madman(?) Point is "all"
amps will have a similiar structure so if you are overwhelmed then
revert back to keep it simple.

 

Hint, some amps even show the audio path, typically for the left channel,
as a bold/highlighted line, eg, Yamaha CR-2020 from hfe.

Wow! They even give you the schematic for their power supply and its pretty simple.  That's a great schematic, I like how it divides up the circuit into portions.

Edited August 16, 2020 by gwurb