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Old 19th September 2010, 04:45 AM   #21
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What are the numbers on the face of 101 and 201?
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Old 19th September 2010, 08:35 AM   #22
tuneman is offline tuneman  Australia
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im pretty sure they were both -
K30A

Last edited by tuneman; 19th September 2010 at 08:39 AM.
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Old 19th September 2010, 02:23 PM   #23
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Measure the DC voltage again but on pin 2 of Q101 this time.
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Old 20th September 2010, 02:33 AM   #24
tuneman is offline tuneman  Australia
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37.5V on center pin on both 101 and 201,
it takes a minute to increase to that voltage! is that normal?
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Old 20th September 2010, 02:48 PM   #25
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When you remove the remote voltage does it immediately drop to 0v?
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Old 21st September 2010, 01:25 AM   #26
tuneman is offline tuneman  Australia
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yes

is it possible the noise could be a partially damaged output transistor? can i test them attatched to the board, and is it the same as in your tutorial?
can i test caps without removing them? theres a few 100uf caps reading 150uf and i was wondering if it was just that there not removed

unfortunatly i have to put the amp back in my car in the next day or so to get it ready for a comp so i won't be doing any more testing till next week,
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Old 21st September 2010, 02:32 AM   #27
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Any damaged transistor could cause this.

You can't test definitively for leakage in the board. You can compare readings and if you have something that seems significantly different, that can lead you to a leaky transistor but you'll have to pull it to determine if it's actually leaking.

This is the same model as is in the tutorial.

Caps can sometimes be checked in the board but that typically requires that you use an ESR meter. A cap tester on a multimeter won't be of much use in most cases. They're not likely the problem, but of course, you can't really rule them out.
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Old 21st September 2010, 03:54 AM   #28
tuneman is offline tuneman  Australia
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i just did another comparison between the dodgy amp and another good one and there seems to be a vast difference between the voltage measuments of Q102 and 201,

will any of these measuments vary with the gain setting of the amp?

like with the good one 2nd pin of q101 and 201 read 12.2v as apposed to 37.5 on the noisy one!
and q101 3rd leg has 32mv as opposed to 23.5 on the noisy one
q201 3rd leg has 26.4mv as opposed to 37.6mv on the noisy one
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Old 21st September 2010, 07:22 PM   #29
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I think the comparison would have to be made with no power applied to the amp. Set you meter to ohms.

You can't compare Q201 and Q102, they're not being used the same way in the circuit.

Do you read ~0 ohms between the first leg of Q201 and the first leg of Q101?

Do you read ~0 ohms between the second leg of Q201 and the second leg of Q101?
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Old 23rd September 2010, 06:08 AM   #30
tuneman is offline tuneman  Australia
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its back in the car at the moment, i'll do some more testing next week, i think it would actually be better if it broke completely this weekend that way it would be easyer to find the problem!
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