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Amp Camp Amp Kit V1.6
Amp Camp Amp Kit V1.6
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Old 16th October 2019, 04:17 PM   #561
bobertbk is offline bobertbk
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Thanks very much Mooly. I'll do an extra close inspection of all the voltages on that one PCB board. I'm hoping the other one is functioning properly given that I was able to set the bias properly.
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Old 16th October 2019, 08:07 PM   #562
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit V1.6
This shows you the typical voltages for a working amp, what you are looking for are gross variations. We know your midpoint voltage won't go above around 0.2 volts on the faulty channel, but that reading should reflect in errors elsewhere, so see where it falls down by measuring.
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Old 18th October 2019, 05:52 AM   #563
bobertbk is offline bobertbk
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The plot thickens. Instead of checking voltage I started by re-checking the resistors. Although I was very careful to place the resistors in the right place I'm getting some strange readings now that they are soldered and the amp is wired up:

Left Board
R8 = .687 (should be 1k)
R9=.5 (should be 1k)
R15=.687 (should be 2.21)

Right Board:
R8=.687 (should be 1k)
R9=.5 (should be 1k)
R11=8k (should be 10k)
r12=8.56k (should be 39.2)

All others are exact or pretty close.
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Old 18th October 2019, 07:47 AM   #564
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit V1.6
You can not reliably check most resistors as long as they are soldered into a circuit because of interactions with other components.

The low supply voltage of the ACA means that any resistor over around 1k could not be damaged by a circuit fault because there just isn't enough voltage to generate the power needed to make the part fail.

Below around 1k and a fault putting the full 24 volts across the resistor could cause over dissipation. So the 100 ohms and the very low resistor values in the output stage are prime candidates for failure in an overcurrent situation.
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Old 18th October 2019, 04:48 PM   #565
bobertbk is offline bobertbk
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Got it. Thanks very much. Prior to checking the resistor values I did also check some of the voltages and every one of them appeared to be off. Is this indicative of potential component damage?

I did remove the boards from the chasis and carefully inspected each solder point to make sure nothing was touching or potentially causing a short circuit.

Are there best practices in situations like this to work my way down a chain to identify root cause?
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Old 18th October 2019, 05:56 PM   #566
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit V1.6
If there was smoke then unfortunately yes, something will be damaged, however knowing the supply voltage is only 24 volts means that we can discount any failures in the physically smaller resistors that are under 1k.

The first thing you need to do is try and establish what has failed now, at this moment in time. That will give a clue as to what has happened, and the way to do that is to measure and record the voltages at the key points in the circuit.

If you want to take this plain image of the circuit and then write all the voltages down that you measure then we should be able to compare to what we know should be present and determine what has happened.
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Old 19th October 2019, 03:44 AM   #567
astromo is offline astromo  Australia
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I'd suggest cross checking the LT Spice info from Mooly with the build guide.

Also, the build guide recommends checking resistance values with a meter before soldering them in to the board.

The guide worked for me, I.e. no smoke ..
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Old 19th October 2019, 10:00 PM   #568
bobertbk is offline bobertbk
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For troubleshooting is it recommended to start at the input (e.g., I'm getting 24v into the board) and work one's way down the circuit to identify root cause?
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Old 20th October 2019, 07:26 AM   #569
Mooly is offline Mooly  United Kingdom
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Amp Camp Amp Kit V1.6
You need to measure several key voltages for us to have any idea where the problem lies.

Measure the DC voltage at all these points and post back with the result.

List them as

A= xxx
B= xxx

and so on.
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Old 23rd October 2019, 04:34 AM   #570
bobertbk is offline bobertbk
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Ok. I took several voltage readings but then I noticed something strange going on. At the V+ input in both boards the voltage is cycling what looks to be between 0v and 24v repeatedly and the LEDs are blinking at the same interval. Might that be something obviously incorrect?
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