I have several vintage amps (NAD, Adcom, NHT, Kenwood) that are in need of repair, re-capping, or adjusting and I'd like to learn how to do this kind of work myself. I'm a retired computer network engineer and do well with self-paced CBT courses. I have soldering skills and more or less recall how to solve DC circuit analysis from my college physics course 40 years ago.
Can someone recommend a good way for me to learn what you think I need to successfully troubleshoot?
Also, I have some basic equipment such as VOM, scope, and ESR. What other equipment will I need to start?
Bob Simon
Can someone recommend a good way for me to learn what you think I need to successfully troubleshoot?
Also, I have some basic equipment such as VOM, scope, and ESR. What other equipment will I need to start?
Bob Simon
Welcome to diyAudio Bob 🙂
What is achievable really depends on your knowledge and ability to learn... learning to adjust equipment and even carrying out improvements (such as replacing old caps or upgrading devices such as opamps) is one thing, fault finding down to component level when presented with a faulty unit is quite another. For that you need a good background in basic electronic theory and how semiconductors operate and behave.
One of the best books (but its not cheap) is this:
https://www.amazon.co.uk/Art-Electronics-Paul-Horowitz/dp/0521809266/ref=dp_ob_title_bk
There are no shortcuts I'm afraid, its all hard won knowledge, but that said it sounds like you are off to a good start with your background and available equipment.
Building simple circuits (no matter what they are) is one the best ways to learn.
These days you can also learn a lot by simulating circuits on the PC (click my signature line for an example of this) but nothing beats actually handling and working with real parts.
Start with easily achievable goals such as refurbishing an old amplifier for example and see how you get on. And don't be afraid to ask questions 🙂
What is achievable really depends on your knowledge and ability to learn... learning to adjust equipment and even carrying out improvements (such as replacing old caps or upgrading devices such as opamps) is one thing, fault finding down to component level when presented with a faulty unit is quite another. For that you need a good background in basic electronic theory and how semiconductors operate and behave.
One of the best books (but its not cheap) is this:
https://www.amazon.co.uk/Art-Electronics-Paul-Horowitz/dp/0521809266/ref=dp_ob_title_bk
There are no shortcuts I'm afraid, its all hard won knowledge, but that said it sounds like you are off to a good start with your background and available equipment.
Building simple circuits (no matter what they are) is one the best ways to learn.
These days you can also learn a lot by simulating circuits on the PC (click my signature line for an example of this) but nothing beats actually handling and working with real parts.
Start with easily achievable goals such as refurbishing an old amplifier for example and see how you get on. And don't be afraid to ask questions 🙂
Thank you for the excellent advice.
While learning to troubleshoot, I'd like to start immediately with "replacing old caps or upgrading devices such as opamps". What do you recommend for short term education for this?
While learning to troubleshoot, I'd like to start immediately with "replacing old caps or upgrading devices such as opamps". What do you recommend for short term education for this?
Troubleshooting is not replacing parts. Our troubleshooting is not different from what you have to do in a computer system - you have to isolate the problem. I agree with the above, learn electronics. My contact with the computer side of the fence tells me they don't get very deep into electronics. Check the power supply and maybe a terst point or two and hte rest is elsewhere. I may be wrong. ANy book on electronic troubleshooting would help, find one that speaks to you. Look up basic audio circuits. We may fancy them up, but the basics are the basics.
My career was in pro audio, wher we don;t worry so much about fancy parts. We do have guys replacing their pedestrian op amps with fancier ones, but the improvements would be only incremental at best, in my view. But that takes little learning. Look up the op amp du jur, and just replace what is there already. Replacing caps is replacing caps. You will find modern caps tend to be physically smaller than the old ones, so occasionally you have to fiddle with mounting. In one system I serviced a lot there were old 5000uf 55v can caps that would age out. Both 5000uf and 55v are not standard values, so we replace them with 4700uf 63v caps. But the lead spacing is not the same either, so we wind up drilling new holes in teh circuit board for them. The change in value? The factory sends out the 4700s in place of the 5000s. I suggest you stick close to stock values for most parts, rather than "if one is good, two is better" approach. SOme guys live to increase power supply caps. DOn;t change cap values unless you have a real reason, a compelling reason, to do so.
Look into doing maintenence, many problems are result of electrically dirty switch contacts, connector pins, controls.
My career was in pro audio, wher we don;t worry so much about fancy parts. We do have guys replacing their pedestrian op amps with fancier ones, but the improvements would be only incremental at best, in my view. But that takes little learning. Look up the op amp du jur, and just replace what is there already. Replacing caps is replacing caps. You will find modern caps tend to be physically smaller than the old ones, so occasionally you have to fiddle with mounting. In one system I serviced a lot there were old 5000uf 55v can caps that would age out. Both 5000uf and 55v are not standard values, so we replace them with 4700uf 63v caps. But the lead spacing is not the same either, so we wind up drilling new holes in teh circuit board for them. The change in value? The factory sends out the 4700s in place of the 5000s. I suggest you stick close to stock values for most parts, rather than "if one is good, two is better" approach. SOme guys live to increase power supply caps. DOn;t change cap values unless you have a real reason, a compelling reason, to do so.
Look into doing maintenence, many problems are result of electrically dirty switch contacts, connector pins, controls.
Just get started with the more simple problems, and you'll learn along the way.
Also, get a basic function generator for a signal source.
Here's a good read for you. DIY Hi-Fi: Vintage Receiver Repair and Modification
Indeed. My background is pro audio as well, and I'd guess that most faults are electro-mechanical, cable or dry joints on offboard connections. Most of the rest would then be noisy caps...
Rayma,
Thanks! The Vintage Receiver Repair article was exactly what I was looking for but I found the part about selecting appropriate capacitance values in Step 3 to be a little confusing.
"When it comes to selecting replacements, make sure the voltage rating of the new cap is higher than the old, as well as capacitance value. But that being said, if the old cap is 250uf, the new one can be 220uf."
Does this mean that if you can't find the value of the original capacitor or a little higher from the mfg you want to use, it's almost always ok to go down by 10-15%?
Bob
Thanks! The Vintage Receiver Repair article was exactly what I was looking for but I found the part about selecting appropriate capacitance values in Step 3 to be a little confusing.
"When it comes to selecting replacements, make sure the voltage rating of the new cap is higher than the old, as well as capacitance value. But that being said, if the old cap is 250uf, the new one can be 220uf."
Does this mean that if you can't find the value of the original capacitor or a little higher from the mfg you want to use, it's almost always ok to go down by 10-15%?
Bob
Learn to desolder parts so neatly that you can not tell that they have been removed and replace. Solder braid and a large iron tip is my preferred method for most stuff. Clean the board around the solder pads with a cotton bud and iso afterwards and you should be able to get a perfect job.
Make sure replacement parts are physically compatible, nothing worse than seeing oversized parts that wont fit the board.
Normally we would usually go up in value if a part was no longer available, particularly if it was in a power supply. If it is in the audio path then the value could be playing a big part in the overall frequency response of the unit. This is where knowledge of how the circuit operates, and exactly what the effect of a value change will be come in. Given that really old parts (electrolytics) probably had a tolerance of at least +50% -20% then using a new 220uf for a 250uf would be fine. If it were in a power supply then a 270 or 330uf could be more suitable.
While swapping opamps can be fun and is mostly straightforward there are potential pitfalls in odd cases. This is where your scope comes in.
This is one of those odd cases:
http://www.diyaudio.com/forums/anal...u-have-checked-see-its-stable-havent-you.html
In order to decide whether you can adjust the value of a part when replacing it, you need to know what role it plays in the circuit. If used as a reservoir, smoother or decoupling cap then a variation of -20% or +50% is of no consequence. In many cases this is also true for a coupling cap. However, if the cap is used as part of a filter (which includes some, but not all, coupling caps) then the value may matter - you may need to be within 10% or even 1%. This assumes audio circuitry; radio gets more complicated!
So there is no substitute for knowledge and understanding, obtained by a combination of reading, thinking and experience.
So there is no substitute for knowledge and understanding, obtained by a combination of reading, thinking and experience.
Reading, reading, and doing...
I haven't really done a whole lot as far as troubleshooting goes, at least not compared to our veteran professionals, and techs, who, by the way often have a more clear view of that aspect of the hobby.
Capacitors have different properties beyond the capacitance, need to read up on that.
Different uses will exploit these different characteristics, and a replacement of parts isn't always a simple choice.
Don't be afraid, but do use the web as a cautious resource until things make sense to you as to what's going on in your particular situation. Always remember that there is probably nothing less subjective either, which also means this a great opportunity to make things how you like them, nothing more, nothing less...
I haven't really done a whole lot as far as troubleshooting goes, at least not compared to our veteran professionals, and techs, who, by the way often have a more clear view of that aspect of the hobby.
Capacitors have different properties beyond the capacitance, need to read up on that.
Different uses will exploit these different characteristics, and a replacement of parts isn't always a simple choice.
Don't be afraid, but do use the web as a cautious resource until things make sense to you as to what's going on in your particular situation. Always remember that there is probably nothing less subjective either, which also means this a great opportunity to make things how you like them, nothing more, nothing less...
Yes, electrolytics have a wide initial value tolerance, and in their typical function
(power supply decoupling, coupling) the capacitance value is not at all critical.
In consumer equipment, the capacitor's voltage rating is often close to the circuit's
operating voltage for cost reasons, so never use an electrolytic with a lower
voltage rating than the original.
There's also the question of temperature rating. Sometimes 105C capacitors are used
instead of 85C types for a longer useful life, either in an elevated temperature environment,
or when there is high ripple current (such as after a rectifier) which causes internal heating.
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Following along here might help?
http://www.diyaudio.com/forums/soli...r-repair-cascade-fail-help-3.html#post4930168
http://www.diyaudio.com/forums/soli...r-repair-cascade-fail-help-3.html#post4930168
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