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Posted: Wed Sep 15, 2010 3:06 pm
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I don't think so, even "bad" soldering doesn't produce 195°C; Re-desolder the Q12/Q14. Did you use thermal paste between the amp heatsink and the transistor heatsink"? Don't forget to resolder the NTC.

The heating is due to over idle current in the power stage. There a couple of possibilities:

Q12/14 are not OK
or the 2 others are not OK.

At last Q12/14 are not mached enough and there is an overcurrent to stabilyze the DC conditions;

Sorry it's very late and I will not on the web until nest tuesday.

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Posted: Sun Sep 19, 2010 10:18 am
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Q12/14 are brand new from Parts-express and are advertised as complementary and share the same data sheet.
http://www.parts-express.com/pdf/TIP147s.pdf

Do you think I should order another pair for Q11/Q13?. They do pass the tests but maybe not compatible with the Darlington.

I actually used paper under the transistors as an insulator for the short term. Is this OK? It is folded several times and thick.

Hurry back Tissan. You know that I can't do this without you. :lol:


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Posted: Sun Sep 19, 2010 11:34 am
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Still in New York city, tomorrow back home

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Posted: Tue Sep 21, 2010 1:09 pm
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Let me know if the transistors Q12/14 and Q11/13 are OK because if the fuse blows there is a short somewhere.

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Posted: Tue Sep 21, 2010 9:26 pm
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Hello Tissan. It is good to hear from you.

It looks like Q11 has a short just as you suggested. I have ordered Darlington TIP142 and TIP 147 to match Q12/Q14.

Q11 tested good earlier. I wonder what happened?


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Posted: Wed Sep 22, 2010 4:41 am
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Probably too hot. Usually these transistors are assembled with a plastic film with thermal past. Let me know if it was the case.

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Posted: Wed Sep 22, 2010 6:44 am
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That may have been the case. The 4 transistors had the plastic film when I removed them but the paste looked worn away. I might not have gotten the film back under Q11. I really am not sure. I will make sure that it is done correctly when I get the new transistors.


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Posted: Wed Sep 22, 2010 12:19 pm
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You should buy a thermal paste also (it's not expensive).

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Posted: Thu Sep 23, 2010 12:39 pm
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Yes I will. Thank you. While I wait for the parts I have to work on my computer. It crashed bad, maybe beyond repair. I am borrowing my daughters laptop to write this.


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Posted: Thu Sep 23, 2010 1:05 pm
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Let me know for the next step.

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Posted: Fri Sep 24, 2010 12:32 pm
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The transitors should be here by Tuesday. I got a Ceramic Thermal Compund to insulate. Its supposed to be good for high temp. Thanks again and I will let you know what happens next week. :D


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Posted: Sat Sep 25, 2010 2:08 pm
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Take care, the thermal compount is not intended to electricaly isolate but to assume thermal transfert from the transistor heat-sink to the big heat-sink;
The plastic film is the isolator.

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Posted: Sat Sep 25, 2010 2:19 pm
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Ok. Thank you. I will insulate with the plastic film.


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Posted: Tue Sep 28, 2010 1:58 pm
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And then ?

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Posted: Tue Sep 28, 2010 5:58 pm
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Sorry to keep you waiting Tissan. Parts-Express sent the wrong part. I got the TIP147 but they sent the wrong part in the TIP142 bag. It was the TIP142 that was bad, so now I have to wait a few more days. It will ship out tomorrow.


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