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Amp Camp Amp Kit V1.6
Amp Camp Amp Kit V1.6
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Old 28th January 2019, 08:53 AM   #431
Alan4411 is offline Alan4411  Wales
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I will admit I am still having some difficulty reconciling some of the measurements. I expect it will become clear once we know what the fault is...

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Originally Posted by Sidsmith View Post
...

then from ground to G (Q2) : 0r
That is a very odd result.
There should be no connection from ground to Q2 G with R5 lifted. Only explanation is a solder blob or wire strand shorting to the heatsink?

There is little point trying anything else, It Is time to take it apart and inspect the rear of the board. Then do some out of circuit checks on the 'transistors'.

Alan
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Old 5th February 2019, 01:09 AM   #432
Sidsmith is offline Sidsmith
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Quote:
Originally Posted by Alan4411 View Post
I will admit I am still having some difficulty reconciling some of the measurements. I expect it will become clear once we know what the fault is...



That is a very odd result.
There should be no connection from ground to Q2 G with R5 lifted. Only explanation is a solder blob or wire strand shorting to the heatsink?

There is little point trying anything else, It Is time to take it apart and inspect the rear of the board. Then do some out of circuit checks on the 'transistors'.

Alan
I will check that tommorow and get back to you.
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Old 12th February 2019, 10:34 PM   #433
garyalex is offline garyalex
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Hi,

I'm a first-time builder and have a question I'm hoping can be answered here. Has anyone had an issue where a potentiometer will not bias? One of the potentiometers displays on my dmm as 25.5v no matter where I set it. The other one behaves as expected. Needless to say, the amp isn't working. Powers up, leds light but no audio output. Not a surprise given my lack of soldering skills.

Thanks,

Gary
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Old 13th February 2019, 03:39 AM   #434
astromo is offline astromo  Australia
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Quote:
Originally Posted by garyalex View Post
Hi,

I'm a first-time builder and have a question I'm hoping can be answered here. Has anyone had an issue where a potentiometer will not bias? One of the potentiometers displays on my dmm as 25.5v no matter where I set it. The other one behaves as expected. Needless to say, the amp isn't working. Powers up, leds light but no audio output. Not a surprise given my lack of soldering skills.

Thanks,

Gary
You could check that the pot is adjusting resistance with power off and your DMM probing the relevant connections. That should rule in/out whether you've flowed solder on to the pot's connections satisfactorily.
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Old 13th February 2019, 03:48 AM   #435
6L6 is offline 6L6  United States
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Amp Camp Amp Kit V1.6
Gary - are you measuring the bias as shown in the guide and it’s always reading the same thing? Do you have an autoranging meter or one where you have to choose the range? If the latter set to DC volts 200.
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Old 13th February 2019, 07:38 AM   #436
Alan4411 is offline Alan4411  Wales
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Gary,
You have probably answered your own question, 90% chance it is a poor solder connection.

First make sure all the components are in their correct place, easy to mix up some resistors. Make sure that Q3 and Q4 are the right way round and that the capacitors are the right way round too.
If you post some good pictures we can take a look as well.

Alan

Edit, where do you get 25.5 volts from? What power supply are you using? Please measure the voltage at the V+ pad on the board to the GND pad.

Last edited by Alan4411; 13th February 2019 at 07:44 AM. Reason: PSU question
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Old 13th February 2019, 04:11 PM   #437
garyalex is offline garyalex
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Quote:
Originally Posted by astromo View Post
You could check that the pot is adjusting resistance with power off and your DMM probing the relevant connections. That should rule in/out whether you've flowed solder on to the pot's connections satisfactorily.
I'll try that. Thanks very much.
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Old 13th February 2019, 04:13 PM   #438
garyalex is offline garyalex
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Quote:
Originally Posted by 6L6 View Post
Gary - are you measuring the bias as shown in the guide and itís always reading the same thing? Do you have an autoranging meter or one where you have to choose the range? If the latter set to DC volts 200.
I am measuring the bias as shown in the guide. It's always 20.5 My meter is not autoranging. It's set to DC volts 200. The bias does measure correctly in the other channel. Thanks.
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Old 13th February 2019, 04:18 PM   #439
garyalex is offline garyalex
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I'll check all that you mention. The voltage measured is actually 20.5. I should also mention that I did search the thread before posting. I found that someone else had the same problem. What resolved the issue for him was not applicable to my amp. I'm sure I soldered something badly. In addition to what you suggest I'm going to try reflowing anything that looks suspicious. I have to say, this feels like a short somewhere. It's definitely down to something I've done wrong. Thanks for the response.
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Old 13th February 2019, 06:35 PM   #440
garyalex is offline garyalex
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Quote:
Originally Posted by Alan4411 View Post
Gary,
You have probably answered your own question, 90% chance it is a poor solder connection.

First make sure all the components are in their correct place, easy to mix up some resistors. Make sure that Q3 and Q4 are the right way round and that the capacitors are the right way round too.
If you post some good pictures we can take a look as well.

Alan

Edit, where do you get 25.5 volts from? What power supply are you using? Please measure the voltage at the V+ pad on the board to the GND pad.
Thanks to the help here I've discovered the problem with that potentiometer. Somehow one of the legs got broken off after insertion. The leg is completely missing in action. Careless handling on my part, no doubt. It wouldn't surprise if I've inadvertently caused other damage as well. I'm considering simply purchasing another parts kit. Thanks again to all who responded.
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