How fudged is my amp?

[mmon77]

Qualified tech are getting fewer and farther between, this is going to become a big problem for the industry… in fact it already is.

Perhaps our government should take a cue from our neighbors to the north and implement something similar to what @byacey was referring to.

I'm aware of one such apprenticeship program run by one of the large tech companies which trains people for industrial automation/electronics. We will need allot more than that though.

 

[agedhorse]

Perhaps our government should take a cue from our neighbors to the north and implement something similar to what @byacey was referring to.

I'm aware of one such apprenticeship program run by one of the large tech companies which trains people for industrial automation/electronics. We will need allot more than that though.

There have been some trade programs, but those techs tend to look for batter paying work, and less hassle, in part because they can... because they are better equipped to do so.

 

[agedhorse]

As a follow-up to this, after a PM discussion with a tech that I respect here on TB, we came to the following reasoning why simply changing parts without diagnostics is a bad idea.

1. we do not know that the emitter resistor next to the burn mark is actually bad, that may have been replaced during a previous repair.

2. The symptoms can be due to a variety of causes, some of which may have nothing to do with the power amp at all. Wouldn’t it be foolish to replace parts on a PCB that isn’t even where the problem is? Worse than that, wouldn’t it be unethical to do this work at the cost to the customer when there was nothing wrong?

3. without doing basic diagnostics, we do not even know what is wrong (preamp, power amp, power supply). Furthermore, these diagnostics need to be done correctly to get accurate information as to what’s NOT right. Incorrect methods results in inaccurate conclusions.

Once the section of the amp (and it may be more than one section) is identified are not working properly, further diagnostics on that section is done to determine the actual fault(s). Once that’s done correctly, a simple analysis and measurements of the circuit should identify the defective components that need replacing.

I’ve written many factory owner/service manuals and documentation in my day (including currently, and many of you have read them too) and taught electronic troubleshooting classes (including university level). This is how it’s approached and executed by the best techs, it’s called “structured troubleshooting”.

The better you understand how the process is supposed to be done, the better equipped you will be to recognize when a tech is not following best practices, being dishonest, or taking advantage of you.

As a consumer, how would you feel if you went to the doctor for serious back pain, were diagnosed with and treated for kidney stones without accurate diagnostics, then after a couple of weeks delay without success you get properly diagnosed and you don’t have kidney stones, you have kidney cancer.

This is why proper diagnostics is important, you can’t treat kidney cancer the same way you treat kidney stones.

 

[dbase]

barfhorse, if it's a sentimental repair, get it done. If I were approached to do it, it's probably be an hours work, and about $10 in parts, especially if you weren't in a hurry and I could simply bundle to parts order into a larger order and save shipping etc. I'd replace both of the TO3 outputs and the emitter resistors as a minimum, and probably the drivers especially if they were a cheap common device like BD139/140s, just to be sure.

If you open any electronic/electrical component and don't know what you're doing, there is the risk you'll get hurt. So, don't do it if you don't know.
Not having a go at you B&C, just emphasising the point as someone who's qualified, and has done thousands of repairs over the years.

Hyperbolic and unlikely. You're far more likely to get dead from shock. See above.

"Barfhorse" ??

 

[A9X]

"Barfhorse" ??

Maybe read the whole thread before commenting. The OPs username is 'barfhorse'.
Discussion in 'Amps and Cabs [BG]' started by barfhorse,

 

[A9X]

As a follow-up to this, after a PM discussion with a tech that I respect here on TB, we came to the following reasoning why simply changing parts without diagnostics is a bad idea.

You are quite obviously having a dig at me. I never stated just replace parts; this is your projection and presumption and a disingenuous one at best. Because I didn't lay out my exact sequence of testing procedures to your satisfaction, tough. You don't usually do it when answering a post either, but up until today I assumed you just did it.
I would speak to the user and look at the unit and inspect it and work out why it failed before I took any action. I was having a guess based upon decades of experience, study etc on an amplifier not in my physical presence, what seemed the most likely course of action based upon what I could see in the pics and the text.

 

[Al Kraft]

I never stated just replace parts; this is your projection and presumption and a disingenuous one at best. Because I didn't lay out my exact sequence of testing procedures to your satisfaction, tough. You don't usually do it when answering a post either, but up until today I assumed you just did it.
I would speak to the user and look at the unit and inspect it and work out why it failed before I took any action. I was having a guess based upon decades of experience, study etc on an amplifier not in my physical presence, what seemed the most likely course of action based upon what I could see in the pics and the text.

As a practicing engineer since the 1970's the first sentence in your second paragraph above is the approach I would expect from a seasoned, professional technician which I expect you are. I think the disconnect came from your original post which I honestly read as sort of skipping or not including that critical step as well:
"...If I were approached to do it, it's probably be an hours work, and about $10 in parts, especially if you weren't in a hurry and I could simply bundle to parts order into a larger order and save shipping etc. I'd replace both of the TO3 outputs and the emitter resistors as a minimum, and probably the drivers especially if they were a cheap common device like BD139/140s, just to be sure...."

In any event, your proposed discussion with the user to get some background and context for the failure and then well-reasoned troubleshooting guided by an understanding of the circuit design itself is right on the mark as the first steps IMO.

Very respectfully,
-Al

 

[A9X]

Thanks Al. If 'we' were discussing this in person, there would have been no misunderstanding. I hate typing long answers and verbally I'm very different.

 

[agedhorse]

Thanks Al. If 'we' were discussing this in person, there would have been no misunderstanding. I hate typing long answers and verbally I'm very different.

I would hope so.

 

[agedhorse]

Maybe read the whole thread before commenting. The OPs username is 'barfhorse'.
Discussion in 'Amps and Cabs [BG]' started by barfhorse,

Was this comment really necessary?

 

[byacey]

... I'd replace both of the TO3 outputs and the emitter resistors as a minimum, and probably the drivers especially if they were a cheap common device like BD139/140s, just to be sure...."

I think this is where much of the contention lies; replacing parts "just to be sure" isn't what I would consider good troubleshooting practice. One should be sure before the new parts are even ordered.

At any rate, an experienced technician may shortcut their troubleshooting based on educated hunches and experience, but to encourage someone with practically no knowledge of what they are doing to dive in and start replacing parts makes the advice-giver complicit in the situation when things go even more-wrong.

 

[A9X]

Was this comment really necessary?

Yes. I answered his question.

 

[agedhorse]

I think this is where much of the contention lies; replacing parts "just to be sure" isn't what I would consider good troubleshooting practice. One should be sure before the new parts are even ordered.

At any rate, an experienced technician may shortcut their troubleshooting based on educated hunches and experience, but to encourage someone with practically no knowledge of what they are doing to dive in and start replacing parts makes the advice-giver complicit in the situation when things go even more-wrong.

Correct, this is what I had addressed.

Yes. I answered his question.

Your bedside manner is even worse than mine, by quite a bit IMO.

 

[A9X]

I would hope so.

Can't resist the snark.

but to encourage someone with practically no knowledge of what they are doing to dive in and start replacing parts makes the advice-giver complicit in the situation when things go even more-wrong.

Don't put words in my mouth. I never said for anyone else to change out parts, I said that based upon my long experience and the tiny cost I would. There are 2 practical reasons; stops that device coming back if they'd been stressed and reduced their functional life, and reduces the chances of it failing in service after repair. I've had to service/repair many devices used in live broadcast where a device going faulty, live and on air, can cost thousands of dollars a minute. A dollar or two spent then can potentially save a fortune and I know which approach was preferred.

 

[A9X]

Correct, this is what I had addressed.


Your bedside manner is even worse than mine, by quite a bit IMO.

Thank you for sharing. Please feel free not to do so in the future.

 

[byacey]

Can't resist the snark.

Don't put words in my mouth. I never said for anyone else to change out parts, I said that based upon my long experience and the tiny cost I would. There are 2 practical reasons; stops that device coming back if they'd been stressed and reduced their functional life, and reduces the chances of it failing in service after repair. I've had to service/repair many devices used in live broadcast where a device going faulty, live and on air, can cost thousands of dollars a minute. A dollar or two spent then can potentially save a fortune and I know which approach was preferred.

If you're not encouraging the original poster, and you're not offering to perform the repairs for him, how is it relevant to this thread?

 

[A9X]

How was the post I replied to?

 

[Al Kraft]

an experienced technician may shortcut their troubleshooting based on educated hunches and experience,

...and even this can sometimes come back to bite you even if you're careful. Most of my experience comes from the military aviation world where time is often a critical factor to support mission execution, but thorough, thoughtful troubleshooting and then proper testing to verify a repair are rarely skipped unless it's an absolute emergency situation. I would add that not spending this time can easily result in an "absolute emergency situation" at the worst possible moment later on.

I do recognize that aviation and weapons related components/sub-systems/systems are more life and death kinds of things than amplifiers, but best practices and sound engineering protocols are pretty much universal IME. The degree to which the risk/reward ratio carries a more severe risk also tends to shape the approach to the repair operations and willingness to take shortcuts to a greater degree, once again IME.

 

[agedhorse]

Following best practices is a good way to avoid the worst outcome.

 

[Al Kraft]

Following best practices is a good way to avoid the worst outcome.

...and I truly wish I wasn't able to cite as many personal examples of where I have proved that to myself.