Words of Wisdom for Amateur DIYers

bhames

New Member
Here are a few words of advice after completing work on a Kenwood 700m as an amateur DIYer. I have worked on a few amps and receivers over the past couple of years as a hobby/enthusiast. I thought I would publish a list of things I have learned in this time to help new DIYers getting into this addicting but satisfying hobby. Here goes.

  • Read, read, read before you do anything. There are multiple posts from very knowledgeable people across multiple boards. Absorb and move forward accordingly. If it doesn't make sense, ask questions. Most people are more than willing to answer your questions.
  • Take pictures of everything from different angles before you start replacing parts. Silk screen errors occur, service manuals don't have all of the changes that have occurred during production, and it helps when putting wires back where they belong.
  • Put screws back into their place immediately after you remove them. For example, when you remove the cover install the screws back into the frame so you know exactly where they go. If you are doing a tear down, there are hundreds of screws of all different sizes. Unless you have a photographic memory or use a thousand plastic bags to keep track of them you will likely end up with a handful of screws that you have no idea where they go.
  • Actually look at the parts/parts numbers on the boards before you order replacements. Don't solely rely upon the service manuals. It is not uncommon for changes to have occurred that aren't in the service manual parts list. Yeah, it sucks sometimes reaching the board that is buried beneath 4 other boards but it sucks more realizing you ordered the wrong capacitor and have to place and wait for another order.
  • Check, double check, and triple check component orientation before soldering. Look back at your pictures for reference.
  • Use a dim bulb tester to validate that you don't have a major issue that will cause more damage if you plug that brand new garage sale find into the wall. By the way, once you pass the dim bulb test, remove the tester from your circuit when measuring/adjusting the piece you are working on. Found out the hard way on this one. Actually found out the hard way on all of these bullet points.
  • Make sure your meter handles the ranges you are trying to measure. I purchased a new Fluke multimeter to replace/supplement a pocket Radio Shack model that I have had for 20 years. I never thought to thoroughly read the specs. It's a Fluke! After multiple sessions of confusion and unnecessary replacement of a few parts, I realized the new Fluke doesn't measure above 60k ohms or lower than 3volts. Ugh.
  • Stock up on alcohol (for cleaning...and a beer afterwards), cotton balls, and q-tips. If the equipment you are working on is anything like the stuff I have dealt with, you will go through a lot of them.
  • Take your time. Unless you are doing this for a business and are on the clock, be patient and don't rush. It is hard to slow down especially when you want to put that baby back into service but calm your motor and take it slow. This is especially hard when you have to make another parts order because you missed a capacitor (or two) that is actually bipolar. Dang it.

Add more words of wisdom as you see fit. Happy repairing.
 
Definitely good basic practices, read, look, think and document. (I'm still to stuborn to put the screws back, will I ever learn?) And the dim bulb or variac is a must, saves headaches.

Make sure your meter handles the ranges you are trying to measure. I purchased a new Fluke multimeter to replace/supplement a pocket Radio Shack model that I have had for 20 years. I never thought to thoroughly read the specs. It's a Fluke! After multiple sessions of confusion and unnecessary replacement of a few parts, I realized the new Fluke doesn't measure above 60k ohms or lower than 3volts. Ugh.

What model fluke is that?
 
I am considering the model 115, but dont see the specs noted you are speaking about. So wonder if that will be the same.
 
Order extra parts to build an inventory - often you'll find you can order twice as many parts for only 20% more plus you save on future shipping costs.

Always wear pants, sox and shoes whilst soldering.
 
The lowest range on the 113 and 115 is 600 ohms with a resolution of 0.1 ohms in that range.

I believe the way to read that spec is that within the range of 0 to 600 ohms the accuracy is .1 ohms. 600 ohms is not the lowest resistance it will measure (I measured 4 ohm resistors just fine.....). Sorry if this is obvious.
 
I believe the way to read that spec is that within the range of 0 to 600 ohms the accuracy is .1 ohms. 600 ohms is not the lowest resistance it will measure (I measured 4 ohm resistors just fine.....). Sorry if this is obvious.
Correct that is what I was saying, the lowest range is 600 ohms. Ohm meters generaly run a fixed DC current through the DUT and measure the voltage needed to get to the targeted current for that range. Each range will use a different amount of current, hence a few ranges and different resolutions. Then its just ohms law.
 
One problem with professional tools for the hobbiests is sometimes they are cratered to a very narrow scope of work.

"The Fluke 113 True RMS AC/DC Utility Multimeter is designed for the utility user, with the features needed to repair most electrical problems encountered by utility workers and linemen everyday."

The ohms functionality on this is probably only intended for continuity testing wires ect. But it's good to have a spare voltmeter.

My father bought me a very expensive high end fluke when I graduated from college. I use it all the time (and appreciate it greatly) but at that time having few tools any full featured DMM and a hoard of other test equipment and tools would have cost him half as much and got me more functionality. I needed decent tools a power supply a good soldering iron, etc, not one really awsome industrial fluke meter. It was like having a beryllium hammer for framing in houses.
 
Be sure that power supply capacitor are discharged, especially with tube equipment. Not all capacitors will discharge when a unit is turned off. This can be shock hazard and even with lower voltages found in SS gear a slip of a probe or screw driver can do damage if it causes a short and the capacitors are not discharged.

If measuring voltages under operating conditions, remember the "keep one hand in your pocket" rule for safety.
Use mini gripers to make connections with the power off and capacitors discharged, then power the unit and make the measurement. It may take a little more time and some of us take short cuts, but it still good advice.

For those starting out, if you will be doing trouble shooting, become familiar with what it takes to make a complete circuit and read a little about Ohm's law (voltage current and resistance). This will help you understand what electricity likes to do and why a less than good, but not necessarily a completely bad solder connection can cause a variety of issues.

The same with dirty switches, controls interconnects, speaker cables and power cables. They may not be completely non functional, but can cause issues with power levels, signal levels, noise and distortion and so on and these symptoms can be intermittent.

Learn to identify parts, resistors, capacitors, inductors, switches and controls, transistors and diode. Learn their schematic symbols.

You do not need to become an engineer unless you want to.

Obtain some junk gear and practice desoldering and soldering parts. Good tools make the work go easier.

And again, above all safety first..
 
Want to add onto the existing points:

Need to learn the basics of transistors.

Need to have understanding of the amplifier circuit. Spend the time, get the schematic on the amp you are working on, study. Calculating the DC voltage on a lot of points on the schematic and compare to the real circuit measurement to make sure you understand the circuit. If you cannot do it, post the schematic here and ask for help. Understanding the circuit is everything.

Don't pull out resistors to measure each of them and then put them back in. Not all resistor are critical, some can be off by 20% and still it's ok. That's where the understanding of the circuit is so important.

Don't pull transistor out and run curve tracer just because you can. DC measurement can tell you whether your transistor has problem or not. If the DC measurement agrees with your calculation, you don't have a problem.

Big filter caps are the ones you need to change from time to time, so it's ok to buy new one regardless whether the voltage is correct or not.



The reason I said don't fix anything if it's not broken is because, every time you stick your soldering iron into the pcb, you are taking a chance of screwing it up. Soldering and desoldering beat up the pcb. Usually the pads for the component has about two to three lives. You pull it out and put it back in, you are taking up lives. Soon, you pull out the pads and you destroy the pcb. As I said, not all resistor has to be accurate, study the circuit and know what is important and what's not. Transistor used usually can take voltage much higher than in the circuit. Just because it fail the curve tracer does not mean it's bad. If the transistor start leaking, you'll see in the DC measurement. Measure a lot, think a lot and do a little. If it is not broken, don't fix it.
 
I believe the way to read that spec is that within the range of 0 to 600 ohms the accuracy is .1 ohms. 600 ohms is not the lowest resistance it will measure (I measured 4 ohm resistors just fine.....). Sorry if this is obvious.

Note that accuracy, precision, and resolution are three different things. As a rule of thumb for any measurement device, don't trust the last digit displayed. If you need something accurate to a tenth of an ohm, measure it with an ohmmeter that reads in hundredths, and so on.
 
For meter, I really don't care about accuracy. One thing very important to me is to be able to read 0.01ohm resolution( not accuracy). It is not for measuring resistance of resistor, it's for finding shorts on pcb. If there is a short, it's usually hard to find, a 4 1/2 digit meter or anything that can read 0.01ohm resolution can really save your day as you get closer to the short, the lower the reading gets. 0.1ohm is not good enough. Fluke that can read this is very expensive, I'd give up everything to get a 4 1/2 digit even if I have to buy a cheap Chinese made.

Auto ranging is good, but I can live without. I won't get too hung up on reading rms AC voltage, duty cycle and all the fancy things. Save the money to buy a scope, you can see these much better. A meter is a meter, I would not trust it to read AC signal, not that the meter cannot do it, it's the long lead that pick up all sort of noise and spoil your reading. You can pay $500 for a fancy meter where you can split the money to get a reasonable meter and get a scope for less than $500 total.........Hell, if you know how to shop, you can even kick in a signal generator for $500!!!
 
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