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Old 10th July 2011, 05:13 PM   #1
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Default Aura Evolution VA100 Mk2. Which transistor is which?

Hello

I have removed 2 transistors Q10 and Q11 in order to fit them on a small heatsink bolted to the PCB. (They get so hot that the solder connecting them to the PCB softens). There is a small chance that I may have muddled the 2 transistors. I think that Q10 should be a BD135 and Q11 should be a BD136. If anyone can say whether I am right or wrong I would be most grateful.

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Old 11th July 2011, 02:33 AM   #2
anatech is offline anatech  Canada
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Hi Greenfingers,
Would you please help us help you by providing the schematic that you're taking your part references from?

My immediate complete guess is that these are regulator transistors (or ICs). Also, a question for you. What are the part numbers on these parts? If these are TL481s, both are the same. See? I have been looking around in an attempt to help you out.

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Old 11th July 2011, 09:11 AM   #3
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yes,BD135 connect positive rail through a 4R7 risistor and its emitter goes to pin7 of the opamp
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Old 12th July 2011, 11:32 AM   #4
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Many thanks for your replies but I have now managed to sort it out for myself with the aid of a textbook.

Regards
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Old 14th July 2011, 08:11 PM   #5
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Thank you awei0822. The information provided in your reply will allow me to power up the amplifier with confidence.
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Old 27th December 2011, 12:58 PM   #6
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Hi,

I have VA80-SE. A few days ago the right channel started to dissapear sometimes is my amp, so I had to look inside. I have noticed that Q11 (BD136, Q11 is the original numbering on the PCB) gets really hot (as mentioned above in this thread). Q10 (BD135) is warm but not worringly. I also noticed that the PCB is a little cooked around Q11. I guess it is not normal condition. Not sure whether it has anything to do with the right channel dissappearing (the sound disaapears but there is still some noise which is also otherwise present when there is no input signal).

Does anybody have the service manual for VA80 (I guess VA100 would do to give me an idea) or any other idea what to check?
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Old 29th December 2011, 08:09 PM   #7
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Hello Gregje
Q10 and Q11 are part of the power supply and therefore any problem with them would not affect only one channel.

I discovered these overheating transistors when investigating an intermittent missing channel. This was due to the solder connecting one of the loudspeaker terminals to the PCB breaking away from the PCB track. The terminal pin had not been fully inserted through the PCB, up to the shoulder, causing the joint to be stressed when the PCB was flexed while the amp was being moved. The case being less than rigid. This or something similar may be the problem with your amp and would be worth a look, although I would expect the speaker to go completely silent.
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Old 31st December 2011, 03:19 PM   #8
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Hi Greenfinger,

Yes I have figured out that these transistors are regulators. One for negative voltage and one for positive. I have noticed that the regulated voltages coming out of these are not the same (I mean the absolute values obviously). I will have to look at these. Meanwhile I added small radiators. I agree that teh power supply would not affect one channel only. I will investigate your suggestion. Thanks!
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