'How to' expansion

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on: October 20, 2016, 09:03:37 AM
 As I go down the path assembling kits and doing other electronic projects, I know that I could do better if only I had the knowledge required to use diagnostic equipment such as an oscilloscope, or sweep generator, or spectrum analyzer. So many times, no matter the simplicity of the project, I find myself stabbing in the dark as to what might have possibly gone wrong. In many cases, I know that the help of one or more of these devices would have quickened the repair. probably there are resources here, and forgive me if I have missed them, but I would be most grateful to find some guidance along these lines.

Offline Paul Birkeland

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Reply #1 on: October 20, 2016, 09:19:32 AM
Having done a ton of repairs over the last couple of years, I can tell you that a scope was helpful for maybe one or two of them.  A sweep generator and spectrum analyzer were never used for any of the repairs that I performed; they are more useful for actual product testing, not looking for an issue.

The tools of a repair tech are generally cheap and low tech.  For our kits a chopstick (that's not too sticky), a random 8 Ohm speaker that's worth nothing to you, a pair of $10 headphones, a pair of shorting plugs, and a DVM are all you're really going to need.


Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Doc B.

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Reply #2 on: October 20, 2016, 09:41:33 AM
I'm with Peebs on this one. The more complex test gear is great for working out a new design, to make sure it functions as intended. But the best tool for repairs is to develop a logical protocol for isolating the cause of the problem with basic tools. Understanding how the circuit should work is the first step to being able to figure out why it isn't working right. I can't overemphasize the importance of that. From there you want to get as much info as you can about the current condition of the piece of gear without causing any further damage. Visual inspection and resistance readings are both low risk ways of gathering that info. If you can't get to the solution with only that info you can proceed carefully to voltage measurements, keeping in mind that additional damage can be caused by powering up broken gear. Take precautions to avoid that, like maybe using a variac or disconnecting parts of the circuit that don't seem to be part of the problem in order to protect them.

Try to think one step ahead. That is to say choose the order of the steps you will take in replacing parts or changing connections in such a way that you get a clear answer as to whether that change is the sole change necessary to fix the problem. For example, if you replace a blown filter capacitor - should you maybe have tested the rectifiers first, since if one is blown it might take out the new capacitor just like the old one?

Within the realm of our kits a lot of this logic has been worked out for you, like the troubleshooting flow chart in the Crack manual. And of course we are happy to help walk someone through the logic of troubleshooting one of our kits on this forum.

All that said, for tough dogs sometimes the test gear is helpful. But even the fancy stuff will not help that much unless you understand the function of the device under test.

Dan "Doc B." Schmalle
President For Life
Bottlehead Corp.