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Cracking beolab penta ( 6601 )

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deVos
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deVos posted on Tue, Feb 12 2019 8:58 AM

Hello all!

I have been new on this forum since tonight so a small proposal round is perhaps in order. I am Richard de Vos and I have been working in the consumer electronics world for years. As a profession but also as a hobby. Knows a lot but not enough, hence my first question here on the forum. Wink

I am working on a beolab penta 6601 whose sound is very distorted from the final stage. After a measurement, it appears that the direct current setting of the output transistors is not OK. Should be about 0.6 V between B and E but there is almost no dc voltage now. The strange thing is that the control voltage sometimes correct and then the speaker also plays fine.

Potentiometer for the DC setting replaced and adjusted it seemed so good to go but unfortunately not ....

I think it is wrong with TR24 here on the base 1.1 V but I measure a negative voltage of around 8V. The basis of TR23 is also not good should be 1.7V but I also measure a negative voltage there. So it seems wrong with TR15 and TR16. I have checked these transistors and the diodes and they all measure well. Does anyone know this error or can someone explain to me how the same voltage setting in this circuit is regulated?

The other side the negative steering on TR29 is fine.

Hope someone is there who can help me out of the dream and am so curious about your reactions!

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