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· Registered
22 Posts
Discussion Starter · #1 ·
This is part of another thread, but I feel could be tread of its own. hoping to get fast help, feel free to link to me things to read.

quick background about components:
I got a bad AVR with a bad front left channel, thats where this items are coming from.

Gear I have:
I have a uni-t ut61 DMM, I have random electrical components from spark fun inventor kit, old PSU can turn in to bench top psu.

I need help checking the components. He is what the circuit is made of and what I think I know:

Resistors :

Look for visual burned marks or cracks.
check to make sure it matches marking and the schematic using dmm

How much ohms do I over look due to % rating of resistor. What about the ohms of my DMM and test leads. I
know this stuff will mess with readings.

This have to be out the circuit to test right?

Noble resistor
Aka fire proof? Aka emitter resistor? Aka sandstone resistor?
What is its name, its big, white has two resistors in one, they share the middle leg.
How do I check it visual, what about with my gear?

Look for blown apart, leaking, or visual damage.
Can this be test in circuit?
Is there a way to test this with equipment I got? If not is there some cheap knockoff from ebay I can buy to test them?

Visual damge what am I looking for?
I know to test for shorts between legs.
How do I test this in with dmm in diode mode? How does this work?
Any other way to test if these test or not the best? I think there is something about apply voltage to a leg and see if it switches??

Diodes :
Visual damage what am I looking for?
My dmm has a test mode, I look to make sure this thing is a one way road right?
Does it have to be out of circuit or can it be in circuit?
Any other info?

There is a variable resistor (rheostat) I think.
I think its used to set something to the right number so that all speakers are in synchronous or sound the same or have same volume. (aka vary a resistance for a specific reason )

I know it need set after you change components. Would I need to set this if I use the exact same components to fix the channel aka rob them from back surrounds?
How do I check this part for damage what do I look for with tools and visually?

Thanks for reading, for your time, and hopefully your help.

· Registered
15,123 Posts
Sorry, but my advice is going to be relatively negative. :(

Your questions suggest that you would benefit from getting some training in electronics, perhaps at a local community college or trade school. That training cannot be easily provided in brief forum threads.

Among other things, you need to get a service manual for the model of device that you're going to be working on. Sadly, repairs on most modern devices consist of replacing entire circuit boards since the time required to do component-level repairs is so expensive and can quickly exceed the value of the hardware. As a result, it might be difficult to find such a manual.

Rather than testing individual components, you need to find out where in the circuitry the signal is being lost or damaged. For this you'll often need an oscilloscope (which you might be able to rent -- they're rather expensive) to view the signals along with a manual (or knowledge) which describes what the signals should look like at each point in the chain. A DMM normally is inadequate for viewing audio signals, although you can use it to check that the DC power supply voltages are OK at each location. However, some DMMs have an AC mode which might be able to measure signal amplitudes when you feed the audio equipment a continuous tone for testing.

Removing components requires proper equipment (de-solderers, anti-static band and mats, etc) plus training and practice. It's extremely easy to damage adjacent integrated circuits by applying too much heat to too large an area, for example, while static electricity can also damage multiple ICs simultaneously and is too easily generated in dry months.

· Registered
13,276 Posts

Specific to your problem, I would start by swapping cables and speakers to ensure the problem is really the receiver and not something else. Swap cables between LF and RF at the AVR and see if the problem follows the cable or stays with the same channel. Then swap speakers to see if the problem follows the speaker or not. That will tell you if the speakers and the cables to them are good (or not). It may help to draw it out or make a table so you can check off each test. If it really is the AVR, start by looking at the connectors and PCB to which they are mounted (most likely) inside the AVR. There may be a bad connector or cracked solder connection on the board. You can also look at the connection from the input board to the rest of the AVR (if it is a separate board). From there it gets harder to debug; the problem could be a bad solder connection on a coupling capacitor or any number of components in line with the signal path.

You could also try a hard reset of the AVR (usually in the manual) to see if that helps.

HTH - Don
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