What is a good starting point for repairing equipment

Young46

Young46

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I was reading a thread started by @fdeelros he started it with referencing voltages on his power supply. I am a hobbyist and have repaired a fair amount of equipment. Most of it with the help of the good techs here on AK. I was curious to know the thoughts on starting the repairs. What is the first thing to do? I don't have an oscilloscope so in some ways that is a big disadvantage I suppose in analysis of the circuits. For me though I don't believe I would ever start another repair without first taking reference voltage readings throughout the amp before anything else. I am asking for people like me who are not trained techs. Any and all comments/advice is appreciated.
 
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I would think the first thing to do is to determine what is not right with the unit. Not the problem that needs a part replaced but something like left channel is weak or both channels out.
 
I agree. Many times I've started to trace fails before actually testing the unit by myself, just believing what the owner said. That's an error I've made several times.

Not all the fails are related to voltages, so I wouldn't say the 1st thing I do is to test voltages.

I'd say the 1st thing to do is to analyze the problem, if a schematic is available it's possible to narrow the problem to a specific area. I do a lot of "homework" before starting to work inside the unit.
 
For training the Navy has this (NEETS) which I've seen recommended over and over - it is on my todo list eventually:

https://www.hnsa.org/manuals-documents/2575-2/

I also have a Raspberry Pi and an Electronics kit made up of a case full of all kinds of electronic parts. Fun lab work to create simple DAC, LED stuff etc.

Edit: But to actually repair stuff etc- training would be most important as kits tell you how to build stuff w/o any education (just a hint of education which isn't nearly enough) on how things work.
 
Blue Shadow said:
I would think the first thing to do is to determine what is not right with the unit. Not the problem that needs a part replaced but something like left channel is weak or both channels out.
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I agree with you but here is where I am. I never had any formal training but I’ve managed to (with the guidance and help from the many techs on AK). I’m 75 years old. I took this hobby up when I retired so I don’t have time to take full blown electronics courses although I wish I could. So (hypothetically) I have an amp and I know what the issue/issues are. For me, before I start I am going to take some voltage readings on the various boards before I begin. For reference. I have wished many times I had done this. It doesn’t take that long and after I’m done will start on the hunt for the specific problem. But I will always have a reference for voltages. It cant hurt.
 
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I haven't updated this in forever but FWIW- http://www.conradhoffman.com/troubleshoottut.htm
It occurs to me that troubleshooting things would be way easier if everything were out in the open and labeled! The first thing I do (or should do) is locate the important circuit nodes. You can't test voltages unless you know where they are, and it's not always that easy. Big dense receivers are the worst. Sometimes I study schematics for a while, since they aren't always models of clarity. I have a scope, several in fact, but I'm a big proponent of troubleshooting with the power off. I want to spot any shorted transistors and fried parts before I ever apply power. I tend to do a lot of probing with an ohmmeter, usually on "diode check", before much else. I also take pictures before touching anything. Now where did that orange wire go again?
 
ConradH said:
I haven't updated this in forever but FWIW- http://www.conradhoffman.com/troubleshoottut.htm
It occurs to me that troubleshooting things would be way easier if everything were out in the open and labeled! The first thing I do (or should do) is locate the important circuit nodes. You can't test voltages unless you know where they are, and it's not always that easy. Big dense receivers are the worst. Sometimes I study schematics for a while, since they aren't always models of clarity. I have a scope, several in fact, but I'm a big proponent of troubleshooting with the power off. I want to spot any shorted transistors and fried parts before I ever apply power. I tend to do a lot of probing with an ohmmeter, usually on "diode check", before much else. I also take pictures before touching anything. Now where did that orange wire go again?
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Words of wisdom ConradH. So true! Yes, those big dense receivers are the worst! Thank you for the link to your information! I should have clarified but the rail voltages are what I am referring to, and sometimes those aren't even in the SM's. At least not all of them. I appreciate all the responses. I'm learning something here!
 
fromnowon said:
I really appreciate it when you guys (who have knowledge) create resources like this. It's awesome. I'm kind of like Young46 I guess; I've fixed a few things with help here and trying to learn more. Just saying thanks I guess and please keep it up!
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Yeah, many thank to all who take time out their busy lives to help! Paying it forward.
 
don't need a scope, need brains.

guy had a receiver, put it in mono, both channels light up. in stereo right is dead

I left instructions that a more tech savvy guy might have extrapolated from. He kept on deflecting. Said he did the switches, and ohmmed them out.

So I used his unfamiliarity to get tests going finally in that area.

I had him working backwards, just injecting hum with his finger at named points, until no hum occurred.
Then zero'd in.

Eventually something clicked, he took over, removing switches, cleaning etc

until it was found that one of the switch leads was not long enough to connect through to the pc pattern. VOILA!! there's the right channel air gap!!

i didn't even call for an ohmmeter. just a noisy finger.
 
Exactly, mtf, understanding what the problem is can lead to solutions that do not need voltages that Y46 wants to get. In your example, not even a meter. This is why my first response said find out what the problems with the unit are and then address those.
 
Blue Shadow said:
Exactly, mtf, understanding what the problem is can lead to solutions that do not need voltages that Y46 wants to get. In your example, not even a meter. This is why my first response said find out what the problems with the unit are and then address those.
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To be clear, I am not advocating taking voltage readings before starting work as a norm or A in the list of instructions for fixing a problem in an amplifier. A certain situation with my amp that I am currently working on caused me to think (that’s dangerous) about the supply voltage to those amp boards. I hope more chime in and share their thoughts. I believe it is very beneficial to those of us who are not trained in electronics repair.
 
ConradH said:
I tend to do a lot of probing with an ohmmeter, usually on "diode check", before much else. I also take pictures before touching anything. Now where did that orange wire go again?
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I do the same. Often people immediately plug in a unit without inspecting first. As @ConradH has said in the past "it's better to have a good plan than a bad plan."
http://www.conradhoffman.com/troubleshoottut.htm
I also inspect ,w/mag. glass, for cold or aged solder joints, evidence of previous repairs, over all condition of age of components. If I had a dime for every cold or aged solder joint fix on A.k.!! More frequent than you may think, Many posts of chasing rabbits to be solved by that simple fix as the problem source all along.
When I am confident it's worth a power test I use the DBT.
 
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Young46 said:
I was reading a thread started by @fdeelros he started it with referencing voltages on his power supply. I am a hobbyist and have repaired a fair amount of equipment. Most of it with the help of the good techs here on AK. I was curious to know the thoughts on starting the repairs. What is the first thing to do? I don't have an oscilloscope so in some ways that is a big disadvantage I suppose in analysis of the circuits. For me though I don't believe I would ever start another repair without first taking reference voltage readings throughout the amp before anything else. I am asking for people like me who are not trained techs. Any and all comments/advice is appreciated.
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Let the symptom(s) be your guide.
 
markthefixer said:
don't need a scope, need brains.

guy had a receiver, put it in mono, both channels light up. in stereo right is dead

I left instructions that a more tech savvy guy might have extrapolated from. He kept on deflecting. Said he did the switches, and ohmmed them out.

So I used his unfamiliarity to get tests going finally in that area.

I had him working backwards, just injecting hum with his finger at named points, until no hum occurred.
Then zero'd in.

Eventually something clicked, he took over, removing switches, cleaning etc

until it was found that one of the switch leads was not long enough to connect through to the pc pattern. VOILA!! there's the right channel air gap!!

i didn't even call for an ohmmeter. just a noisy finger.
Click to expand...
I'm having a similar issue, however it's the left channel that doesn't function on stereo, functional in mono.exchanged the board with another that those switches are mounted on, both board switches were cleaned prior to assembly. No change in results. The sliders function from left to right in mono but stereo in only right channel responded both boards.
 
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